Understanding Your Kidney Blood Tests

The core markers are creatinine and eGFR (estimated glomerular filtration rate). Creatinine is the raw blood measurement; eGFR is a calculated estimate of how well your kidneys filter, derived from creatinine together with your age and sex. Supporting markers include BUN (urea), albumin, bicarbonate, and electrolytes such as potassium, phosphorus, and calcium. The uACR urine test is also essential because it detects protein leakage, an early sign of kidney damage.

A normal eGFR is generally 90 or above. Values between 60 and 89 can be normal if there is no other evidence of kidney damage. Below 60 for more than three months indicates chronic kidney disease. Below 15 is kidney failure. eGFR naturally declines slightly with age, so a slightly reduced number in an older adult is not always pathological.

It depends on your CKD stage. Stable Stage 1–2 patients may be tested once a year. Stage 3 typically every 6 months. Stage 4 every 1–3 months. Stage 5 and dialysis patients are tested even more frequently. If your trend is changing, your nephrologist will usually increase the frequency.

No. Creatinine is a waste product measured directly in the blood. eGFR is a calculation that uses your creatinine along with age and sex to estimate your kidney filtration rate. Because eGFR accounts for body-size differences, it is a more useful clinical number — but creatinine is still what the lab actually measures.

eGFR fluctuates for many reasons: hydration level, recent meals (especially protein-heavy), vigorous exercise, some medications, and even the time of day the blood was drawn. A single change is rarely meaningful. What matters is the trend over multiple tests — that is what your nephrologist uses to assess progression.