Blood tests ordered for swollen feet
| Test | Normal Range | Why it's done |
|---|---|---|
| Albumin | 3.5–5.0 g/dL | Low albumin = fluid leaks into tissues (oedema) |
| Creatinine / eGFR | eGFR >60 mL/min | Kidney disease causing fluid retention |
| BNP / NT-proBNP | BNP <100 pg/mL | Heart failure marker — swelling from poor heart pump |
| TSH | 0.4–4.0 mIU/L | Hypothyroidism causes non-pitting oedema (myxoedema) |
| LFT (Albumin, Bilirubin) | Albumin >3.5 g/dL | Liver cirrhosis causing protein loss and fluid retention |
| CBC | Hb Men >13.5 g/dL | Anaemia — can cause leg oedema |
| Urine protein | Negative | Nephrotic syndrome — kidneys losing protein |
| D-Dimer | <0.5 mg/L | DVT (deep vein thrombosis) — clot causing one-sided swelling |
What causes swollen feet and ankles?
Heart failure
When the heart is not pumping effectively, blood backs up in the veins, causing fluid to leak into the surrounding tissues. This causes bilateral (both legs) pitting oedema — swelling that leaves a dent when pressed. Swelling is worse in the evening and after standing. BNP or NT-proBNP is the key blood test — elevated levels indicate the heart is under strain. A chest X-ray and echocardiogram (heart ultrasound) are usually arranged.
Kidney disease / Nephrotic syndrome
Kidneys damaged by diabetes, hypertension or glomerulonephritis may lose protein into the urine (proteinuria). Low blood protein (low albumin) means less oncotic pressure to hold fluid in blood vessels — fluid leaks into tissues. Swelling is often first noticed around the eyes in the morning. Urine protein and albumin are the key tests. eGFR tells you how much kidney function is left.
Liver disease / Cirrhosis
The liver makes albumin. When the liver is severely damaged (cirrhosis), albumin production falls, causing protein-losing oedema. Liver cirrhosis also raises pressure in the portal vein (portal hypertension), causing fluid to accumulate in the abdomen (ascites) and legs. LFT will show low albumin, raised bilirubin, and raised INR.
Hypothyroidism (underactive thyroid)
Low thyroid hormone causes a unique type of swelling called myxoedema — a non-pitting oedema caused by mucopolysaccharide deposits under the skin. Unlike pitting oedema, pressing the skin does not leave a dent. TSH will be elevated. This resolves with thyroid hormone replacement (levothyroxine).
Deep Vein Thrombosis (DVT)
A blood clot in the deep veins — usually the calf or thigh — causes one-sided swelling, pain, warmth and redness. DVT is a medical emergency because clots can break off and travel to the lungs (pulmonary embolism). D-Dimer is the initial blood test — if elevated, a Doppler ultrasound of the leg veins confirms the diagnosis.
Venous insufficiency and other benign causes
Chronic venous insufficiency (leaky leg vein valves) is a common cause of bilateral ankle swelling — especially in people who stand for long periods or are overweight. Pregnancy, certain medications (calcium channel blockers, steroids, NSAIDs), and prolonged sitting during travel (economy class syndrome) also commonly cause foot oedema. Blood tests are usually normal.
Pitting vs non-pitting oedema
| Type | What it is | Common causes |
|---|---|---|
| Pitting oedema | Leaves a dent when pressed for 5 seconds | Heart failure, kidney disease, liver disease, DVT, pregnancy |
| Non-pitting oedema | No dent — skin bounces back | Hypothyroidism (myxoedema), lymphoedema |
Questions to ask your doctor
- Is my swelling one-sided or both sides? (One-sided suggests DVT)
- What is my albumin level?
- Do I need an echocardiogram (heart ultrasound)?
- Is any of my medication causing or worsening swelling?
- Do I need compression stockings?