Screening for Microalbuminuria Simplified by Urine Specific Gravity

Abstract

Background: The albumin-to-creatinine ratio and the 24-hour urine collection to measure microalbuminuria are inconvenient and expensive. The newer rapid and less expensive dipstick methods for screening of microalbuminuria estimate only albumin and are subject to errors caused by variation in volume. We determined the relation between urine-specific gravity (Usg) and urine creatinine (Ucr) so that Ucr can be derived from Usg to correct for albumin concentration in the urine which is influenced by urine volume. Methods: We randomly included 42 consecutive patients from the primary care clinic, and 34 patients from the diabetic clinic. Results: We found that a very good correlation existed between Usg and Ucr in the 42 patients from the primary care clinic (Ucr = 11.4 × Usg –11,509, r = 0.83, p < 0.001). Patients from the diabetic clinic who had well-controlled blood sugar (n = 21) showed a similar trend (Ucr = 10.82 × Usg –10,882, r = 0.87, p < 0.001). However, this was not the case with uncontrolled diabetics (Ucr = 2.53 × Usg –2,513, r = 0.26, NS). Using simple arithmetic, we derived a simplified formula where Ucr can be predicted from Usg. Using multiple regression to incorporate the urinary glucose level by dipstick, a more generic formula was obtained for estimating urinary creatinine. Conclusion: Usg can be used instead of Ucr to normalize for the varied urine concentration while screening for microalbuminuria. Poorly controlled diabetics should be screened after their blood sugars are well controlled or use the more generic formula that incorporates urinary glucose. Thus, by measuring spot urine albumin and specific gravity by dipsticks one gets an easy, immediate and accurate estimation of microalbuminuria in an office setting.