Microalbuminuria. Invalidity of simple concentration-based screening tests for early nephropathy due to urinary volumes of diabetic patients.

Abstract

To evaluate the possibility of replacing quantitative albumin excretion rate (AER) measurements with rapid screening tests for microalbuminuria. 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). 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. To evaluate incipient nephropathy, we recommend quantitative measurements of N-AER from timed urine collections only. Dipstick tests are either insensitive or nonspecific.