Using a first morning urine sample to measure albumin-creatinine ratio in patients with type 2 diabetes and renal disease offers the best predictor of renal events, according to a new study.
Researchers used data from the industry-funded RENAAL (Reduction In Endpoints in Non Insulin Dependent Diabetes Mellitus with the Angiotensin-II Antagonist Losartan) study to compare methods of measuring proteinuria in patients with type 2 diabetes and kidney disease. The four methods tested were urinary protein excretion from a 24-hour urine collection, urinary albumin excretion from a 24-hour urine collection, urinary albumin concentration from a first morning urine sample and albumin-creatinine ratio from a first morning urine sample. The study's primary outcome measure was time to doubling of serum creatinine concentration or time to end-stage renal disease. The results were published early online July 15 by the Journal of the American Society of Nephrology.
Seven hundred one patients with type 2 diabetes and nephropathy collected both a first morning urine sample and a 24-hour urine sample. Of these, 202 (28.8%) had a doubled serum creatinine concentration or developed end-stage renal disease during follow-up. Hazard ratios for renal outcome risk per SD increment in each measure were 3.16 (95% CI, 2.60 to 3.86) for urinary albumin excretion, 3.02 (95% CI, 2.53 to 3.62) for urinary protein excretion, 3.23 (95% CI, 2.67 to 3.91) for urinary albumin concentration and 4.36 (95% CI, 3.50 to 5.45) for albumin-creatinine ratio. The albumin-creatinine ratio had a significantly higher area under the receiver-operating curve than the other measures.
The authors cautioned that their results are not generalizable to patients without diabetes and nephropathy, but concluded that measuring albumin-creatinine ratio in first morning urine is the best way to predict progression of renal disease in this population. An accompanying editorial concurred, stating, “Given data from this study and the considerable patient effort required for a 24-hour urine collection, we agree with the authors that the first morning [albumin-creatinine ratio] is in general the logical choice for quantifying proteinuria in clinical practice.”