Kidney function tests explained

Kidney function tests are blood and urine tests that measure how well your kidneys are filtering waste and maintaining fluid and electrolyte balance. The most common are serum creatinine, estimated glomerular filtration rate (eGFR) and urine albumin-to-creatinine ratio.

Abnormal results can be caused by dehydration, medications, high blood pressure, diabetes, kidney infections, obstruction, or chronic kidney disease. Sometimes results are temporarily affected by illness or muscle breakdown rather than reflecting true kidney damage.

eGFR estimates how much blood your kidneys filter per minute, with lower values indicating reduced function, while raised urine albumin suggests the kidney's filtering units are leaking protein. Your doctor interprets these together with your overall health picture rather than any single number in isolation.

It depends on the degree and how quickly it develops: a sudden drop in kidney function needs urgent assessment, whereas mild, stable reductions over time may simply need monitoring and lifestyle adjustment. Chronic, worsening kidney function can eventually lead to kidney failure if unmanaged.

Some causes of reduced kidney function, such as dehydration or certain medications, are reversible once addressed. Chronic kidney disease generally can't be reversed, but its progression can often be slowed significantly with blood pressure control, diabetes management and appropriate medication.

They usually involve a simple blood test and a urine sample, sometimes combined with imaging such as an ultrasound if an abnormality is found. No special preparation is usually needed, though your doctor may ask you to avoid certain foods or medications beforehand.

People with risk factors such as diabetes, high blood pressure or a family history of kidney disease are typically tested annually, while those with known kidney disease may need more frequent monitoring. Your GP will advise on the right interval for your individual risk.

Creatinine is the raw blood measurement of a waste product filtered by the kidneys, while eGFR is a calculated estimate of kidney filtering capacity that accounts for creatinine alongside age, sex and sometimes ethnicity. eGFR gives a more standardised picture of overall kidney function than creatinine alone.

Any significantly abnormal or rapidly worsening kidney function result should be discussed with a doctor promptly, as timely action can prevent further damage. Private nephrology consultations can typically be arranged within about two weeks, considerably faster than standard NHS referral routes.