Validity of random urines to quantitate proteinuria in children with human immunodeficiency virus nephropathy

Accurate assessment of proteinuria in pediatric patients infected with the human immunodeficiency virus (HIV) is limited by constraints imposed by timed urine collections and low creatinine excretion in very ill patients with low muscle mass. We therefore sought to validate the use of random urine specimens to quantitate total protein and creatinine excretion in a population of 236 HIV-positive children. A mathematical derivation for estimating urine volume (V) was constructed. The accuracy of the final calculation [V = 832 (kL/Ucr)BSA] (where k = constant, L body length, UCr urine creatinine and BSA body surface area) was tested by regression analysis comparing the calculated and measured volume of 31 urines from ambulatory HIV-negative patients. The correlation coefficient was highly significant (r = 0.77, P ≤ 0.0001). The relationship was also applied to 23 timed urine specimens from HIV-positive patients with similar significance (r = 0.87, P < 0.0001). A regression analysis of measured proteinuria against the urine protein: creatinine ratio (U(pr)/U(Cr)) in these same urines from the HIV-positive patients yielded a significant relationship both in the linear (r = 0.95, y = 0.4x) and the logarithmic regression (r = 0.97, y = x + 0.4). These data support the use of random U(pr)/U(Cr) ratios to estimate daily proteinuria in HIV-infected pediatric patients despite low creatinine excretion rates. The previously accepted values continue to apply, with U(pr)/U(Cr) ≤ 2.0 considered normal and > 2.0 representative of nephrotic proteinuria.