Edema most commonly affects the lower extremities — feet, ankles, and legs — because gravity pulls fluid downward. But swelling can occur anywhere: around the eyes, in the hands, in the abdomen (ascites), or throughout the body (anasarca). The location, timing, and associated symptoms provide important clues about the underlying cause.

The body maintains a delicate balance of fluid distribution. When this balance is disrupted — whether by heart problems affecting circulation, kidney problems affecting fluid excretion, liver problems affecting protein production, thyroid dysfunction affecting metabolism, or other conditions — fluid leaks from blood vessels into surrounding tissues, causing swelling.

This article explores the different types of edema, what underlying conditions might be responsible, and what blood tests can reveal about why you’re retaining fluid.

Understanding Swelling and Edema

To understand edema, it helps to understand how the body normally manages fluid. This fluid balance is one of the most tightly regulated systems in the body — and when it fails, the results are visible as swelling.

Blood circulates through vessels, delivering oxygen and nutrients to tissues. Fluid constantly moves between blood vessels and surrounding tissues through capillary walls. This movement is governed by pressure gradients (pushing fluid out) and protein concentrations (pulling fluid back in). At the arterial end of capillaries, pressure pushes fluid out into tissues; at the venous end, osmotic forces pull most of it back. The lymphatic system picks up the rest and returns it to the bloodstream.

This delicate balance involves several key factors:

• Hydrostatic pressure: The pressure of blood pushing fluid out of vessels. This pressure is highest in arteries and lower in veins. When venous pressure increases — whether from heart failure backing up blood, venous insufficiency with valve damage, or obstruction blocking blood return — more fluid is pushed out into tissues and less is reabsorbed.
• Oncotic (colloid osmotic) pressure: The “pulling” force created by proteins (especially albumin) in the blood. Proteins are too large to easily cross capillary walls, so they create an osmotic gradient that draws fluid back into blood vessels. When protein levels drop — from kidney disease losing protein in urine, liver disease failing to produce protein, or malnutrition lacking protein intake — this pulling force weakens, fluid leaks out into tissues and stays there.
• Capillary permeability: How “leaky” blood vessel walls are. Normally, capillary walls allow fluid and small molecules to pass but retain proteins and blood cells. Inflammation, allergic reactions, burns, and certain diseases increase capillary permeability, allowing more fluid and even proteins to escape into tissues.
• Lymphatic drainage: The lymphatic system is a network of vessels that collects excess fluid from tissues and returns it to the bloodstream. It’s like a cleanup crew, picking up what the venous system misses. When lymphatics are blocked (from surgery, radiation, infection, or developmental abnormalities) or overwhelmed, fluid accumulates — this is lymphedema.
• Kidney function: The kidneys are the master regulators of total body fluid. They control how much water and sodium are retained or excreted, responding to hormonal signals to maintain blood volume and blood pressure. When kidney function declines, the body loses this precise control, typically retaining more sodium and water than it should.
• Hormonal regulation: Multiple hormones influence fluid balance, including antidiuretic hormone (ADH), aldosterone, and natriuretic peptides. Dysregulation of these systems — as occurs in heart failure, liver disease, and other conditions — contributes to fluid retention.

Edema occurs when any of these mechanisms is disrupted, causing fluid to accumulate in tissues faster than it can be removed. Understanding which mechanism is affected helps identify the underlying cause and guide appropriate testing.

Types and patterns of edema:

Pitting edema: When you press firmly on swollen tissue for several seconds and it leaves an indentation (pit) that slowly fills back in, this is pitting edema. It’s the most common type of edema and indicates that fluid (rather than other substances) has accumulated in the interstitial space between cells. Healthcare providers grade pitting edema by the depth of the pit (1+ to 4+) and how long it takes to resolve — deeper and longer-lasting pits indicate more severe edema. Pitting edema is characteristic of heart failure, kidney disease, liver disease, and venous insufficiency.

Non-pitting edema: Swelling that doesn’t leave an indentation when pressed — or leaves only a minimal, quickly resolving pit. The tissue may feel firmer, “doughy,” or “woody.” Non-pitting edema is characteristic of lymphedema (where protein-rich fluid accumulates because lymphatics can’t drain it) and myxedema (severe hypothyroidism, where mucopolysaccharides accumulate in tissues). The distinction between pitting and non-pitting edema is clinically important because it suggests different underlying causes and different treatment approaches.

Peripheral edema: Swelling in the extremities, most commonly the feet, ankles, and legs. This is where gravity-dependent edema accumulates when a person is upright — fluid follows gravity to the lowest point. The degree of peripheral edema is often described by how far up the leg it extends: ankle edema, edema to mid-calf, edema to the knee, or edema extending to the thigh. In people who are bedridden, “gravity-dependent” edema may accumulate in the sacral area (lower back and buttocks) instead of the legs.

Periorbital edema: Swelling around the eyes, often most noticeable in the morning. This occurs because lying flat overnight allows fluid to redistribute to the face. Periorbital edema is particularly characteristic of nephrotic syndrome (kidney disease with protein loss) but can also occur with allergic reactions, thyroid disease, contact dermatitis, or simply fluid shifts from sleeping position.

Pulmonary edema: Fluid accumulation in the lungs, filling the air spaces and interfering with oxygen exchange. This is not visible as external swelling but causes shortness of breath, especially when lying flat (orthopnea), coughing (sometimes producing pink frothy sputum), and crackling sounds heard with a stethoscope. Pulmonary edema usually indicates left-sided heart failure and is a medical emergency requiring immediate treatment.

Ascites: Fluid accumulation in the abdominal (peritoneal) cavity, causing abdominal distension. The abdomen may appear swollen and feel full of fluid; healthcare providers can detect a “fluid wave” on examination. Ascites is most commonly associated with liver cirrhosis (where portal hypertension and low albumin combine to drive fluid into the abdomen) but can also occur with heart failure, certain cancers, kidney disease, and other conditions.

Anasarca: Severe, generalized edema affecting the entire body — face, trunk, arms, legs, and sometimes even genitals. Anasarca indicates a serious underlying condition with major disruption of fluid balance, typically advanced heart failure, severe kidney failure (nephrotic syndrome), advanced liver failure, or severe malnutrition. It requires urgent medical evaluation.

Characteristics that suggest specific causes:

Bilateral symmetric swelling (both legs equally): When swelling affects both legs to a similar degree, it suggests a systemic cause rather than a local problem. The body is retaining fluid throughout, and gravity pulls it to the lowest point. Common systemic causes include heart failure, kidney disease, liver disease, severe venous insufficiency affecting both legs, medication side effects, or hormonal factors. This pattern is where blood tests are most valuable — they can identify or rule out the major organ-based causes.

Unilateral swelling (one leg significantly more than the other): Asymmetric swelling suggests a local cause affecting one limb. The most concerning is deep vein thrombosis (DVT) — a blood clot blocking venous return from one leg. Other causes include cellulitis (bacterial skin infection causing inflammation and swelling), lymphedema (often affects one limb more than the other), injury or trauma, localized venous insufficiency, or compression of veins by tumor or other mass. Unilateral swelling requires different evaluation than bilateral, though some blood tests (D-dimer for DVT) may be relevant.

Swelling worse at end of day: This pattern is common with venous insufficiency and prolonged standing or sitting. Throughout the day, gravity pulls fluid into the lower legs; without adequate venous return, it accumulates. Overnight, with legs elevated in bed, fluid redistributes and swelling improves — only to recur the next day. Heart failure also typically causes end-of-day swelling that improves overnight.

Swelling worse in morning, especially around eyes: This pattern is characteristic of kidney disease, particularly nephrotic syndrome. During sleep, fluid redistributes to the face and periorbital area (which has loose tissue that readily swells). Upon waking and standing, gravity moves the fluid back to the legs over several hours. If facial puffiness is prominent in the morning, kidney disease should be strongly considered.

Swelling with shortness of breath: This combination is concerning for heart failure (where the failing heart causes both fluid backup in the lungs and in the periphery) or severe anemia (where oxygen delivery is compromised). Shortness of breath that’s worse when lying flat (orthopnea) or that wakes the person from sleep (paroxysmal nocturnal dyspnea) strongly suggests heart failure with pulmonary congestion.

Swelling with rapid weight gain: Rapid weight gain over days (not gradual gain over months) almost always represents fluid retention rather than fat accumulation. One liter of retained fluid weighs approximately one kilogram (2.2 pounds). A person with heart failure or kidney disease may gain several pounds in just a few days during a fluid overload episode. Tracking daily weight is an important monitoring tool for people with these conditions.

When to be concerned:

Seek medical evaluation for edema that:

• Is new and doesn’t have an obvious benign explanation
• Is progressive — clearly getting worse over days or weeks
• Affects only one leg (could indicate DVT, which is urgent)
• Is accompanied by shortness of breath at rest or with minimal activity
• Is accompanied by chest pain or pressure
• Includes abdominal swelling (ascites)
• Is accompanied by noticeably decreased urine output
• Occurs with rapid weight gain (several pounds in a few days)
• Is accompanied by fever and redness of the skin (possible infection)
• Doesn’t improve with leg elevation and reduced sodium intake

Emergency warning signs:

Seek immediate medical care for:

• Sudden severe swelling in one leg with pain, warmth, or redness: This may indicate deep vein thrombosis, which can lead to life-threatening pulmonary embolism if a clot breaks loose
• Swelling with severe shortness of breath, especially if unable to lie flat: May indicate pulmonary edema from heart failure — a medical emergency
• Swelling with chest pain or difficulty breathing: Could indicate heart attack or pulmonary embolism
• Facial or throat swelling with difficulty breathing or swallowing: May indicate severe allergic reaction (anaphylaxis) requiring immediate treatment
• Swelling during pregnancy with severe headache, vision changes, or upper abdominal pain: Warning signs of preeclampsia, which can be life-threatening for mother and baby

Heart Problems: A Leading Cause of Edema

Heart failure is one of the most important causes of edema to identify because it’s common (affecting millions of people), it’s treatable (many effective medications exist), and it’s serious (untreated heart failure is progressive and life-threatening). When the heart can’t pump blood efficiently, pressure builds up in the venous system, forcing fluid out of blood vessels and into surrounding tissues.

It’s important to understand that “heart failure” doesn’t mean the heart has stopped — it means the heart isn’t pumping as effectively as the body needs. The heart is still working, but it’s not keeping up with demands. This can happen gradually over years (chronic heart failure) or suddenly (acute heart failure).

How heart failure causes edema:

The heart is a pump — actually two pumps working in series. The right side receives blood returning from the body and pumps it to the lungs for oxygen; the left side receives oxygenated blood from the lungs and pumps it out to the body. When either side’s pumping ability is compromised, blood backs up in the system behind it.

• Right-sided heart failure: When the right side of the heart can’t effectively pump blood forward to the lungs, pressure backs up in the veins returning blood from the body. This increased venous pressure — transmitted all the way to the capillaries in the legs, abdomen, and throughout the body — pushes fluid out of blood vessels and into tissues. The result is peripheral edema (swelling in the legs, ankles, and feet), hepatic congestion (liver enlargement), and sometimes ascites (abdominal fluid). Right-sided failure often develops secondary to left-sided failure but can occur primarily from lung disease (cor pulmonale), pulmonary hypertension, or right-sided valve disease.
• Left-sided heart failure: When the left side of the heart can’t effectively pump blood forward to the body, pressure backs up in the pulmonary veins draining the lungs. This increased pressure in the pulmonary circulation forces fluid into the air spaces of the lungs — pulmonary edema. This causes shortness of breath (dyspnea), which is often worse when lying flat (orthopnea) because more blood returns to the chest in the recumbent position. People may wake at night gasping for air (paroxysmal nocturnal dyspnea) or be unable to sleep flat, needing multiple pillows or to sleep in a chair. Severe pulmonary edema is a medical emergency.
• Both sides often fail together: In practice, most heart failure involves both sides to some degree. Left-sided failure, over time, leads to right-sided failure as increased pulmonary pressures strain the right heart. The result is combined symptoms: both pulmonary congestion (shortness of breath) and systemic venous congestion (peripheral edema, hepatic congestion).

What causes heart failure:

• Coronary artery disease: The most common cause. Reduced blood flow to the heart muscle (ischemia) or heart attacks damage the heart’s pumping ability.
• Hypertension (high blood pressure): The heart has to work harder against elevated pressure. Over years, this stress causes the heart muscle to thicken and eventually weaken.
• Valve disease: Damaged or diseased heart valves (stenosis or regurgitation) make the heart work harder and can lead to failure.
• Cardiomyopathy: Disease of the heart muscle itself, which can be genetic, caused by alcohol, viral infections, or other factors.
• Arrhythmias: Chronic abnormal heart rhythms (like atrial fibrillation) can weaken the heart over time.
• Other conditions: Diabetes, thyroid disease, obesity, and other conditions contribute to heart failure risk.

Characteristics of heart failure edema:

• Bilateral, symmetric swelling — both legs affected similarly
• Pitting edema — leaves a clear indentation when pressed
• Gravity-dependent — worse in the legs when upright, shifts to the back (sacral area) when lying down
• Typically worse at the end of the day after being upright for hours
• Improves somewhat overnight with leg elevation but returns during the day
• May progressively extend up the legs — from ankles to calves to knees to thighs as heart failure worsens
• Often accompanied by shortness of breath (especially with exertion or lying flat), fatigue, and reduced exercise tolerance
• May have visible neck vein distension (elevated jugular venous pressure) — a sign of right heart backup
• Rapid weight gain from fluid retention — pounds added over days, not months
• May have enlarged liver (hepatomegaly) from congestion

Blood tests for heart-related edema:

BNP (B-type Natriuretic Peptide) or NT-proBNP: These are the most important blood tests for evaluating whether heart failure is causing edema. BNP is a hormone released by heart muscle cells when they’re stretched or under stress — essentially, when the heart is working too hard. Elevated BNP levels strongly suggest heart failure as the cause of edema. Conversely, normal BNP levels make heart failure very unlikely, effectively ruling it out as the cause. This makes BNP testing extremely valuable for quickly distinguishing cardiac from non-cardiac causes of swelling. NT-proBNP is a related marker with similar utility but different reference ranges.

Complete blood count: Anemia (low hemoglobin) can cause or worsen heart failure because the heart has to work harder to deliver adequate oxygen when the blood’s oxygen-carrying capacity is reduced. Identifying and treating anemia can improve heart failure symptoms.

Kidney function tests (creatinine, eGFR): Heart failure and kidney disease often coexist and worsen each other — a relationship called “cardiorenal syndrome.” Poor cardiac output reduces kidney perfusion; kidney dysfunction leads to fluid retention that worsens cardiac load. Kidney function also affects medication choices and dosing.

Electrolytes (sodium, potassium): May be abnormal in heart failure and are affected by common heart failure medications (diuretics, ACE inhibitors). Low sodium in heart failure can indicate more advanced disease.

Liver function tests: Severe right heart failure causes “hepatic congestion” — blood backs up into the liver, which may become enlarged and tender. This can elevate liver enzymes (particularly alkaline phosphatase and bilirubin) and impair liver synthetic function.

Thyroid function (TSH): Both hypothyroidism and hyperthyroidism can cause or worsen heart failure. Hypothyroidism causes bradycardia and myocardial dysfunction; hyperthyroidism increases metabolic demands and can cause rapid atrial fibrillation. Thyroid testing is routinely recommended in new heart failure evaluation.

Kidney Disease: When the Body Can’t Excrete Fluid

The kidneys are the body’s primary regulators of fluid balance, filtering about 180 liters of blood daily and adjusting how much water and sodium are retained or excreted based on the body’s needs. They respond to hormonal signals, blood pressure, and blood volume to maintain this exquisite balance. When kidney function is impaired, the body loses this regulatory capacity, and fluid inevitably accumulates.

Kidney-related edema is one of the most important causes to identify because kidney disease is common (affecting an estimated 15% of adults to some degree), often asymptomatic until advanced, progressive if not managed, and associated with significantly increased cardiovascular risk.

How kidney disease causes edema:

Reduced glomerular filtration: The kidneys contain millions of tiny filtering units called nephrons. Each nephron filters blood through a structure called the glomerulus, removing waste products while retaining useful substances. When nephrons are damaged — whether by diabetes (the leading cause), hypertension, glomerulonephritis, or other conditions — filtration capacity declines. The kidneys simply can’t excrete excess fluid, sodium, and waste products as efficiently. This leads to volume overload — too much fluid in the body — and edema.

Sodium retention: Even before complete kidney failure, damaged kidneys often retain more sodium than normal. Multiple mechanisms contribute: reduced filtration of sodium, activation of the renin-angiotensin-aldosterone system (which promotes sodium retention), and impaired response to natriuretic hormones (which normally promote sodium excretion). Since sodium holds water, sodium retention leads directly to fluid retention and edema.

Protein loss — nephrotic syndrome: Certain kidney diseases damage the glomerular filtration barrier, allowing protein (especially albumin) to leak from blood into urine. Normally, this barrier keeps large molecules like proteins in the bloodstream. When damaged, substantial amounts of albumin can be lost daily. Low blood albumin has profound consequences: albumin creates oncotic pressure — the force that pulls fluid back into blood vessels from tissues. With low albumin, this pulling force weakens, so fluid leaks out of blood vessels into tissues and stays there. The result is dramatic edema. Nephrotic syndrome is defined by heavy proteinuria (protein in urine), low serum albumin, edema, and often elevated cholesterol.

Characteristics of kidney-related edema:

• Periorbital edema (puffiness around the eyes): This is particularly characteristic of nephrotic syndrome and often one of the earliest signs. It’s typically most noticeable in the morning after lying flat overnight (allowing fluid to redistribute to the face) and may improve throughout the day as fluid moves to the lower body.
• Bilateral leg swelling: Often quite significant, potentially extending from feet to thighs. The edema is typically pitting (leaves an indentation).
• May include abdominal swelling (ascites): In severe cases, fluid accumulates in the abdominal cavity as well as the periphery.
• Foamy or frothy urine: Particularly in nephrotic syndrome, the high protein content in urine causes visible foaming when urinating — similar to egg whites being beaten.
• Decreased urine output: As kidney function declines, total urine production may decrease, though this is variable.
• Often associated with hypertension: The kidneys play a central role in blood pressure regulation. Kidney disease commonly causes or worsens hypertension, which in turn accelerates kidney damage — a vicious cycle.
• Fatigue and weakness: Kidney disease causes anemia (because kidneys produce erythropoietin, which stimulates red blood cell production) and accumulation of waste products, both contributing to fatigue.
• May have other uremic symptoms: In advanced kidney disease, accumulating toxins cause nausea, loss of appetite, metallic taste, itching, and cognitive changes.

Blood tests for kidney-related edema:

Creatinine and BUN (Blood Urea Nitrogen): Creatinine is a waste product from muscle metabolism that’s normally filtered out by the kidneys. When kidney function declines, creatinine accumulates in the blood — elevated creatinine is one of the primary indicators of reduced kidney function. BUN also rises with declining kidney function but is less specific (it’s affected by protein intake, dehydration, and other factors).

eGFR (estimated Glomerular Filtration Rate): Calculated from creatinine (and sometimes cystatin C), age, sex, and race, eGFR estimates how many milliliters of blood the kidneys filter per minute. It’s the standard measure for staging chronic kidney disease. Normal eGFR is above 90; eGFR below 60 sustained for 3 months indicates chronic kidney disease; eGFR below 15 indicates kidney failure requiring dialysis or transplant consideration.

Albumin: Low serum albumin is a hallmark of nephrotic syndrome. Albumin below about 3.5 g/dL (varies by lab) combined with heavy protein in urine strongly suggests nephrotic syndrome. The lower the albumin, the more severe the edema tends to be.

Urinalysis: Examines urine for protein, blood, and other abnormalities. Significant protein in urine (proteinuria) indicates kidney damage affecting the filtration barrier. Blood in urine (hematuria) may indicate glomerulonephritis or other conditions. Urinalysis is simple, inexpensive, and essential for kidney evaluation.

Urine protein/creatinine ratio or 24-hour urine protein: Quantifies how much protein is being lost in urine. Nephrotic-range proteinuria (greater than 3.5 grams per day, or equivalent ratio) confirms nephrotic syndrome. This quantification guides treatment decisions.

Electrolytes: Kidney disease affects electrolyte balance. Potassium may be elevated (hyperkalemia) because the kidneys normally excrete excess potassium. This is important because high potassium can cause dangerous heart rhythm problems. Sodium may be low, normal, or elevated depending on the specific situation.

Complete blood count: Kidney disease causes anemia, typically normocytic (normal-sized red cells) and often not fully explained by iron deficiency. The kidneys produce erythropoietin (EPO), the hormone that stimulates red blood cell production in bone marrow. Damaged kidneys produce less EPO, leading to “anemia of chronic kidney disease.”

Liver Disease: When Protein Production Fails

The liver produces albumin, the main protein responsible for maintaining oncotic pressure in blood vessels. When the liver is severely damaged (cirrhosis), albumin production drops, fluid leaks into tissues, and edema develops. Liver disease also causes portal hypertension, which contributes to fluid accumulation, particularly in the abdomen.

How liver disease causes edema:

Low albumin production: The cirrhotic liver can’t synthesize adequate albumin. Low serum albumin means reduced oncotic pressure, so fluid leaks from blood vessels into tissues and can’t be pulled back.

Portal hypertension: Scarring in cirrhosis blocks blood flow through the liver, increasing pressure in the portal vein (which drains the intestines). High portal pressure forces fluid into the abdominal cavity (ascites) and contributes to leg edema.

Sodium and water retention: Liver disease activates hormonal systems that cause the kidneys to retain sodium and water, worsening fluid accumulation.

Characteristics of liver-related edema:

• Ascites (abdominal swelling) is often prominent and may appear before leg edema
• Leg edema typically bilateral
• May have other signs of liver disease: jaundice (yellowing of skin and eyes), spider angiomas (small red vascular marks), palmar erythema (red palms), easy bruising
• Often accompanied by fatigue and weakness
• May have history of alcohol use, hepatitis, or other liver disease

Blood tests for liver-related edema:

Albumin: Low albumin is characteristic of advanced liver disease. The lower the albumin, the more severe the liver dysfunction.

Liver function tests (AST, ALT, bilirubin, alkaline phosphatase): These may be elevated in active liver disease. However, in cirrhosis, AST and ALT may be only mildly elevated or even normal because there’s little functioning liver tissue left to release enzymes.

PT/INR (Prothrombin Time/International Normalized Ratio): The liver produces clotting factors. Prolonged PT/INR indicates impaired liver synthetic function and increased bleeding risk.

Complete blood count: Cirrhosis often causes thrombocytopenia (low platelets) due to splenic sequestration and reduced thrombopoietin production. Anemia may also be present.

Hepatitis serologies: Hepatitis B and C are major causes of cirrhosis worldwide and should be tested.

Thyroid Dysfunction and Edema

Thyroid disorders can cause edema through several mechanisms, and the pattern of swelling can differ between hypothyroidism and hyperthyroidism.

Hypothyroidism and myxedema:

Hypothyroidism can cause a distinctive type of edema called myxedema — the accumulation of mucopolysaccharides (glycosaminoglycans) in tissues. Unlike typical pitting edema, myxedema is often non-pitting: when you press on it, it doesn’t leave an indentation because the swelling is from accumulated substances, not just fluid.

Characteristics of hypothyroid-related swelling:

• Facial puffiness, particularly around the eyes
• Swollen hands and feet
• Non-pitting or only slightly pitting quality
• Skin may feel cool, dry, and thickened
• Often accompanied by other hypothyroid symptoms: fatigue, cold intolerance, weight gain, constipation, slow heart rate, dry skin, hair loss

Severe hypothyroidism can also cause fluid retention through effects on heart function and kidney function.

Hyperthyroidism:

Hyperthyroidism, particularly Graves’ disease, can cause pretibial myxedema — a distinctive swelling on the shins (anterior tibial area). This is actually an autoimmune phenomenon related to Graves’ disease rather than a direct effect of excess thyroid hormone. The skin becomes thickened, with an “orange peel” texture.

Additionally, if hyperthyroidism leads to heart failure (which can occur with prolonged uncontrolled hyperthyroidism), typical cardiac edema may develop.

What to test:

TSH: The primary screening test for thyroid dysfunction. Elevated TSH indicates hypothyroidism; suppressed TSH indicates hyperthyroidism.

Free T4 and Free T3: Measure actual thyroid hormone levels if TSH is abnormal.

TPO antibodies: Identify autoimmune thyroid disease (Hashimoto’s causing hypothyroidism, or associated with Graves’ disease).

Nutritional Causes of Edema

Severe nutritional deficiencies can cause edema, though this is less common in developed countries. The primary mechanism is protein deficiency leading to low albumin.

Protein-calorie malnutrition:

Severe protein deficiency (kwashiorkor) causes dramatic edema due to low albumin. This is most common in famine conditions or with severe underlying disease causing malnutrition. In developed countries, it may occur with:

• Severe eating disorders (anorexia nervosa)
• Chronic alcoholism with poor diet
• Malabsorption syndromes
• Cancer cachexia
• Elderly individuals with poor nutrition

Thiamine (Vitamin B1) deficiency:

Severe thiamine deficiency causes beriberi, which can present as “wet beriberi” with heart failure and edema. This occurs primarily with chronic alcoholism or in populations dependent on polished rice. The heart failure is reversible with thiamine replacement.

What to test:

Albumin and total protein: Low levels indicate protein deficiency from any cause.

Prealbumin (transthyretin): A more sensitive marker of recent protein status than albumin because it has a shorter half-life.

Thiamine (B1): If wet beriberi is suspected, particularly in alcoholics.

Other Causes of Edema

Venous insufficiency:

Chronic venous insufficiency occurs when leg veins can’t efficiently return blood to the heart, usually due to damaged valves. Blood pools in the lower legs, increasing venous pressure and causing fluid to leak into tissues. This is very common, especially in older adults, and causes:

• Swelling worse at the end of the day and after prolonged standing
• Improvement with leg elevation overnight
• Often accompanied by varicose veins, skin discoloration (brown staining), and eventually skin changes (lipodermatosclerosis)
• Usually affects both legs but may be asymmetric

Venous insufficiency is primarily a clinical diagnosis, but blood tests may be done to rule out other causes.

Medications:

Many medications can cause edema as a side effect:

• Calcium channel blockers (amlodipine, nifedipine): Very common cause of ankle edema — affects up to 10-25% of users. Dilates arteries more than veins, increasing capillary pressure.
• NSAIDs (ibuprofen, naproxen): Cause sodium and water retention by affecting prostaglandins in the kidney.
• Corticosteroids: Cause sodium retention and fluid accumulation.
• Thiazolidinediones (pioglitazone): Diabetes medications that cause fluid retention.
• Gabapentin, pregabalin: Can cause peripheral edema.
• Estrogen-containing medications: Oral contraceptives and hormone replacement therapy can cause fluid retention.

Medication-related edema typically resolves when the medication is stopped or changed.

Lymphedema:

Lymphedema occurs when the lymphatic system can’t adequately drain fluid from tissues. It may be:

• Primary: Due to developmental abnormalities of the lymphatic system
• Secondary: Due to damage or obstruction — commonly from lymph node removal for cancer treatment, radiation, infection (filariasis in tropical regions), or trauma

Lymphedema is typically non-pitting (or minimally pitting) and doesn’t respond to diuretics. It’s diagnosed clinically rather than through blood tests.

Deep vein thrombosis (DVT):

A blood clot in a deep leg vein causes acute unilateral swelling with pain, warmth, and sometimes redness. DVT is a medical emergency because the clot can break loose and travel to the lungs (pulmonary embolism).

D-dimer: A blood test that measures a clot breakdown product. Elevated D-dimer suggests active clotting but is not specific to DVT (many conditions elevate D-dimer). A normal D-dimer helps rule out DVT; an elevated D-dimer requires imaging (ultrasound) to confirm or exclude the diagnosis.

Allergic reactions:

Allergic reactions can cause localized swelling (hives, angioedema) or, in severe cases, generalized swelling. Angioedema particularly affects the face, lips, tongue, and throat. Severe cases (anaphylaxis) are medical emergencies.

Pregnancy:

Some edema is normal in pregnancy due to increased blood volume and pressure from the enlarging uterus on pelvic veins. However, sudden or severe edema, especially with hypertension, proteinuria, headache, or visual changes, may indicate preeclampsia — a serious pregnancy complication requiring immediate medical attention.

The Testing Strategy for Edema

Blood tests help identify systemic causes of edema. The appropriate tests depend on the clinical picture.

Core tests for evaluating significant or unexplained edema:

Complete metabolic panel:

• Creatinine, BUN, eGFR — kidney function
• Albumin — low levels indicate kidney disease, liver disease, or malnutrition
• Electrolytes — affected by heart, kidney, and liver disease
• Liver enzymes — liver disease screening

BNP or NT-proBNP: Essential for evaluating whether heart failure is contributing. Very useful for distinguishing cardiac from non-cardiac causes.

Urinalysis: Protein in urine suggests kidney disease. Heavy proteinuria indicates nephrotic syndrome.

Complete blood count: Anemia can worsen heart failure; various abnormalities may indicate underlying disease.

TSH: Thyroid dysfunction is a treatable cause of edema.

Additional tests based on clinical suspicion:

• D-dimer: If DVT is suspected (unilateral swelling)
• PT/INR: If liver disease is suspected
• Hepatitis serologies: If liver disease is suspected
• Urine protein quantification: If nephrotic syndrome is suspected
• Thiamine level: If nutritional deficiency or alcoholism

What to Do With the Results

If heart failure markers are elevated (high BNP):

Heart failure requires comprehensive evaluation including echocardiogram to assess heart function. Treatment typically includes diuretics (to remove excess fluid), medications to improve heart function (ACE inhibitors, beta-blockers), sodium restriction, and treatment of underlying causes (hypertension, coronary artery disease).

If kidney function is impaired:

Kidney disease requires evaluation of the cause and severity. Treatment focuses on managing blood pressure, controlling diabetes if present, avoiding nephrotoxic medications, and dietary modifications. Severe kidney disease may require dialysis.

If albumin is low:

Low albumin from liver disease indicates significant liver damage requiring hepatology evaluation. Low albumin from nephrotic syndrome requires nephrology evaluation and treatment of the underlying kidney disease. Low albumin from malnutrition requires nutritional support.

If thyroid dysfunction is found:

Hypothyroidism is treated with thyroid hormone replacement; hyperthyroidism with medications, radioactive iodine, or surgery. Edema typically improves as thyroid function normalizes.

When Tests Are Normal

Normal blood tests narrow the possibilities:

• Venous insufficiency: Very common cause of leg edema with normal blood tests. Diagnosed clinically; may need vascular evaluation.
• Medication-related edema: Review all medications, particularly calcium channel blockers and NSAIDs.
• Dependent edema from prolonged sitting or standing: Common, benign, improves with leg elevation and movement.
• Lymphedema: Diagnosed clinically; blood tests are typically normal.
• Idiopathic edema: A syndrome of fluid retention, predominantly in women, without clear underlying cause.

Lifestyle Approaches for Managing Edema

These strategies can help reduce swelling regardless of cause (but don’t replace treatment of underlying conditions):

• Reduce sodium intake: Sodium holds water. Limiting salt helps reduce fluid retention. This means not just the salt shaker but also processed foods, restaurant meals, and canned goods.
• Elevate legs: When sitting, elevate legs to heart level or above to help fluid drain back toward the heart. Sleep with legs slightly elevated if tolerated.
• Avoid prolonged standing or sitting: Take breaks to walk and move. If you must sit for long periods, do ankle pumps and calf exercises.
• Wear compression stockings: Graduated compression stockings help prevent fluid accumulation in the legs, particularly for venous insufficiency.
• Exercise regularly: Movement helps pump fluid out of the legs through muscle contraction. Walking is particularly effective.
• Stay hydrated: Paradoxically, dehydration can worsen fluid retention as the body tries to hold onto water. Drink adequate fluids unless instructed otherwise.
• Maintain healthy weight: Excess weight worsens venous return and increases heart workload.
• Limit alcohol: Alcohol affects fluid balance and can worsen edema, particularly with liver disease.

The Bottom Line

Swelling that persists or progresses often signals an underlying condition affecting how the body handles fluid. The major organ systems involved — heart, kidneys, liver, and thyroid — can all be assessed through blood testing, making edema evaluation straightforward in many cases. Identifying the cause is essential because effective treatment depends on addressing the underlying problem, not just the symptom of swelling.

Heart failure, kidney disease, and liver disease are the most important systemic causes to identify because they’re serious, common, and treatable with the right interventions. Blood tests including BNP (for heart function), creatinine and eGFR (for kidney function), albumin (which is low in both kidney and liver disease), and TSH (for thyroid function) can quickly narrow the diagnostic possibilities and guide appropriate treatment.

The pattern of edema provides important diagnostic information. Bilateral leg swelling suggests systemic causes that blood tests can identify; unilateral swelling raises concern for deep vein thrombosis requiring urgent evaluation. Facial puffiness, especially in the morning, points toward kidney disease. Shortness of breath accompanying edema suggests heart failure or pulmonary involvement.

If you’re experiencing persistent swelling, particularly if it’s accompanied by shortness of breath, affects only one leg, includes abdominal distension, or is rapidly progressing, medical evaluation is important. Don’t ignore new or worsening edema — it’s often your body signaling that something needs attention. The right blood tests can identify treatable causes and put you on the path to effective management, reducing swelling and addressing the underlying condition before it causes further harm.

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Key Takeaways

• Edema has many causes — the pattern of swelling (which areas, pitting vs. non-pitting, bilateral vs. unilateral) provides diagnostic clues
• Heart failure is a leading cause — BNP or NT-proBNP testing can quickly identify or rule out cardiac causes
• Kidney disease causes edema through fluid retention and protein loss — creatinine, eGFR, albumin, and urinalysis are key tests
• Liver disease causes edema through low albumin and portal hypertension — often presents with ascites
• Thyroid dysfunction can cause distinctive swelling patterns — TSH testing should be included in evaluation
• Many medications cause edema — particularly calcium channel blockers and NSAIDs
• Unilateral leg swelling requires urgent evaluation — may indicate deep vein thrombosis
• Venous insufficiency is very common — causes leg edema with normal blood tests
• Swelling with shortness of breath is concerning — may indicate heart failure or pulmonary embolism
• Lifestyle modifications help — reducing sodium, elevating legs, compression stockings, and exercise can reduce swelling