For many people, albuminuria is the earliest sign of CKD. A urine albumin-to-creatinine ratio (UACR) on a spot urine specimen is the recommended test to assess and monitor urine albumin.
UACR is a ratio between two measured substances.
Urine Albumin (mg/dL) = UACR in mg/g ≈ Albumin excretion in mg/day
Urine Creatinine (g/dL)
- Unlike a dipstick test for albumin, UACR corrects for variation in urine concentration
- The first morning void is preferred because more concentrated urine allows for enhanced detection of analytes present in small quantities
- A random urine sample, collected while the patient is in the office, is also acceptable if a first morning void is not available
- A 24-hour urine collection is not necessary for routine assessment
Urine albumin is a continuous risk factor. UACR greater than 30 mg/g is considered abnormal. Traditionally, 30–300 mg/g has been called microalbuminuria and greater than 300 mg/g has been called macroalbuminuria. However, the 300 mg/g cut-off merely represents a rough correlation with the lower limit of sensitivity of the traditional urine dipstick for albumin. Thus, the albuminuria cut-offs are derived from laboratory methods rather than clinically relevant endpoints.
Stable or lower levels of albuminuria may indicate therapy is effective. Increasing or elevated levels may indicate progression of CKD.
- Urine albumin excretion is an early predictor of cardiovascular disease morbidity and mortality and renal function loss
- Decreasing excessive dietary protein and sodium to healthful levels, and use of angiotensin converting enzyme (ACE) inhibitors and angiotensin receptor blockers (ARB), may lower albumin excretion
The NKDEP Laboratory Working Group, in collaboration with the International Federation of Clinical Chemistry and Laboratory Medicine, has undertaken an effort to standardize the laboratory assessment of urine albumin and the reporting of results to clinicians.