The albumin-to-creatinine ratio (ACR) is a spot urine test that screens for kidney damage by measuring how much albumin leaks into the urine relative to creatinine excretion. This calculator computes the ACR and classifies the result into a KDIGO albuminuria category, the same A1/A2/A3 scale used alongside eGFR to stage chronic kidney disease.
How the albumin/creatinine ratio works
A healthy kidney's glomerular filtration barrier keeps most albumin — a relatively small, negatively charged blood protein — out of the urine. When that barrier is damaged, as happens early in diabetic nephropathy, hypertensive kidney disease, and many other CKD causes, albumin begins to leak into the urine before other markers of kidney function change.
Because urine concentration varies throughout the day with hydration, a raw albumin concentration from a single spot sample can be misleading. Dividing albumin by creatinine — which is excreted at a relatively constant rate — normalizes for this variation, so a convenient spot sample can substitute for a cumbersome 24-hour urine collection. The KDIGO 2024 guideline sets the diagnostic thresholds this calculator uses: A1 under 30 mg/g, A2 from 30 to 300 mg/g, and A3 over 300 mg/g.
Inputs and what they mean
Urine albumin can be entered in mg/dL or mg/L — pick whichever unit matches your lab report using the toggle. Urine creatinine is entered in mg/dL, the conventional US unit; if your lab reports creatinine in µmol/L, use the Unit Conversion tab first.
Both values should come from the same urine sample, ideally a first-morning void, which minimizes the effect of posture and daytime physical activity on measured albumin excretion. A random spot sample is an acceptable alternative when a first-morning sample isn't practical.
Limits and edge cases
ACR is a screening tool, not a standalone diagnosis. Several factors can transiently raise a single ACR reading independent of true kidney damage: vigorous exercise in the preceding 24 hours, fever or acute illness, urinary tract infection, uncontrolled hyperglycemia, marked hypertension, heart failure, and menstruation. KDIGO guidance recommends confirming an elevated ACR with repeat testing — commonly 2 of 3 positive results over 3 months — before diagnosing persistent albuminuria.
ACR alone does not stage CKD; it is one axis (the "A" in KDIGO's CGA framework) that is combined with the cause of kidney disease and the eGFR-based GFR category (G1–G5) to assess overall risk. This calculator does not replace a treating clinician's full evaluation, which should include a repeat confirmatory test, eGFR, and the broader clinical picture.