Kidney Function Tests: Creatinine, eGFR and What They Mean
A plain explanation of the blood and urine tests used to assess kidney function, and how the results are interpreted.
Last updated: 2026-09-24
Kidney function is assessed with inexpensive blood and urine tests. The two most important are serum creatinine, converted into an estimated filtration rate (eGFR), and the urine albumin-to-creatinine ratio, which detects protein leak.
The core tests
- Serum creatinine — a waste product of muscle, cleared by the kidneys
- eGFR — an estimate of filtration rate calculated from creatinine
- Urea (blood urea nitrogen) — a second waste marker
- Urine albumin-to-creatinine ratio — the earliest sign of kidney damage
Interpreting results
A single abnormal value does not establish disease. Dehydration, diet, recent exercise and some medicines can shift creatinine temporarily. The clinically meaningful signal is the trend over time, ideally across at least three months.
Who should be tested
Annual testing is advisable for anyone with diabetes, high blood pressure, a family history of kidney disease, heart disease, or age over 60 — regardless of symptoms.
Frequently asked questions
What is a normal creatinine level?
Roughly 0.6–1.2 mg/dL in adults, but it varies with muscle mass, age and sex, which is why the eGFR is the more informative number.
Do I need to fast before a kidney function test?
Usually not, although some laboratories request fasting when the panel is combined with glucose or lipids. Follow the instruction given at your laboratory.