Swollen Ankles: Could It Be Your Kidneys?

Why do ankles and legs swell?

Swelling — known medically as oedema — happens when fluid builds up in the body’s tissues. Gravity pulls that fluid downward, so it collects most visibly in the ankles, feet and lower legs. Pressing the skin may leave a dent that slowly fills back in (pitting oedema).

Oedema has many causes, from standing too long to heart, liver or vein problems. But one important and sometimes overlooked cause is kidney disease, and recognising it can lead to early diagnosis of a treatable condition.

How the kidneys cause swelling

The kidneys influence body fluid in two main ways:

• Protein loss (nephrotic syndrome): When the kidneys’ filters are damaged, large amounts of albumin leak into the urine. Albumin normally keeps fluid inside the blood vessels, so when its level drops, fluid escapes into the tissues — producing widespread swelling, classically around the eyes in the morning and in the ankles by evening.
• Fluid and salt retention: As kidney function declines, the kidneys remove less salt and water from the body. The extra fluid raises blood pressure and accumulates in the legs.

Both mechanisms can occur together, and both connect swelling directly to protein in the urine — the key link your nephrologist will look for.

Distinguishing kidney oedema from other causes

The pattern of swelling offers clues, though tests are needed to confirm:

• Kidney oedema is typically symmetrical (both legs), may appear around the eyes first thing in the morning, and often comes with foamy urine and raised blood pressure.
• Cardiac oedema (from heart failure) usually worsens through the day and is accompanied by breathlessness, especially when lying flat.
• Venous oedema (from varicose veins or a clot) is often one-sided, with skin changes or discomfort in that leg.

These distinctions guide which specialist and which tests you need.

The connection to protein in urine

When swelling is caused by the kidneys, the single most telling finding is protein in the urine. Heavy protein loss points to nephrotic syndrome and conditions such as glomerulonephritis or diabetic nephropathy. This is why a urine test is one of the first things a nephrologist requests when assessing unexplained leg swelling.

What tests are needed?

A focused assessment usually includes:

• Urine tests — dipstick and albumin-to-creatinine ratio to detect and quantify protein loss.
• Blood tests — albumin level, creatinine, eGFR and cholesterol.
• Blood pressure measurement.
• Kidney ultrasound when structural problems need excluding.
• Additional tests — such as a heart scan, if a cardiac cause is also being considered.

When to seek urgent care

Most leg swelling can be assessed in a routine appointment, but some situations need prompt attention. Seek same-day care if swelling is accompanied by breathlessness, chest pain, a sudden painful swelling in one leg, or a sharp fall in urine output.

If your swelling is persistent, symmetrical or comes with foamy urine, a nephrology assessment is the right step. Dr. Juan Luis Villaro Gumpert evaluates oedema at Hospital Vithas 9 de Octubre in Valencia, in English and Spanish, and provides clear records you can share with your own doctor abroad.