How effective is a blood test for chronic kidney disease?

A blood sample can measure creatinine, a waste product cleared by the kidneys, and can be used to estimate filtration. A raised result may reflect kidney disease, but it can also be affected by muscle mass, dehydration, recent strenuous activity or some medicines. Chronic kidney disease means an abnormality persists or there is other evidence of kidney damage, so one result is not enough.

A clinician may compare results over time and arrange a urine test for albumin or blood. Blood pressure, diabetes, medicines and previous illnesses also help put the result into context.

Attend the test as arranged and tell the clinician about supplements, prescribed medicines, vomiting, diarrhoea or reduced fluid intake. Do not stop a medicine without advice. Ask whether the result should be repeated, whether a urine sample is needed, and how it compares with earlier results. A kidney function result may guide monitoring or referral rather than provide a diagnosis immediately.

Seek prompt medical advice for much less urine than usual, new swelling of the legs or face, breathlessness, persistent vomiting, confusion or severe weakness. These symptoms can have several causes but may indicate a significant illness. Seek emergency care for severe breathing difficulty, collapse or marked confusion.

Ask which kidney markers were measured, whether the result needs repeating, whether urine testing or an ultrasound is appropriate, and which medicines or painkillers should be reviewed.