Microalbuminuria: Invalidity of Simple Concentration-Based Screening Tests for Early Nephropathy Due to Urinary Volumes of Diabetic Patients

OBJECTIVE: To evaluate the possibility of replacing quantitative albumin excretion rate (AER) measurements with rapid screening tests for microalbuminuria. RESEARCH DESIGN AND METHODS: Dipstick-negative specimens from 363 consecutive insulin-dependent diabetes mellitus (IDDM) and 46 non-insulin-dependent diabetes mellitus (NIDDM) patients from primary-care and hospital clinics (11% inpatients) within the district of Turku University Hospital were studied. Albumin concentrations and 12-h nightly excretion rates (N-AER) were measured by nephelometry (sensitivity 2 mg/L). RESULTS: An increased N-AER (greater than 15 micrograms/min) was seen in 99 IDDM (27%) and 15 NIDDM (33%) patients. The median urinary volume was 900 ml/12 h, with a maximum of 3000 ml. At the level of 20 mg albumin/L, the sensitivity to detect elevated N-AER was 70% among IDDM patients and 60% among NIDDM patients. At a lower albumin concentration of 10 mg/L, the sensitivities were increased to 91 and 87% in IDDM and NIDDM patients, respectively, but the specificities were reduced to 77 and 71%, respectively. CONCLUSIONS: To evaluate incipient nephropathy, we recommend quantitative measurements of N-AER from timed urine collections only. Dipstick tests are either insensitive or nonspecific.