ABSTRACT

Objective: Whereas measurement of albumin:creatinine ratio (ACR) in spot urine samples is indicated for determining microalbuminuria, its performance or that of urinary albumin excretion rate (UAER) in predicting microalbuminuria in sickle cell disease (SCD) is unclear. We therefore tested the diagnostic performance of these measures in spot and timed urine samples in predicting a UAER in 24-hour samples.

Methods: Thirty participants with SCD had spot, two-hour and four-hour, followed by 24-hour urine collections for ACR, urinary albumin concentration (UAC) and UAER determinations. Receiver operating characteristic (ROC) curve analyses were performed.

Results: The areas under the ROC curves for microalbuminuria were 0.99 (CI: 0.97, 1.00) for ACR and 0.97 (CI: 0.92, 1.00) for UAC in spot urine samples. For ACR, at the cut-point of 4.13 mg/mmol, there was 100% sensitivity and 82.6% specificity, allowing an 86.2% correct classification. At the cut-point of UAC = 20.9 mg/L, there was 100% sensitivity and 73.9% specificity, allowing a 79.3% correct classification. Corresponding areas for microalbuminuria in two-hour timed samples were 0.99 (CI: 0.95, 1.00) for ACR and 0.96 (CI: 0.89, 1.00) for UAER.For ACR, the cut-point was 4.64 mg/mmol with 83.3% sensitivity and 91.3% specificity, allowing an 89.7% correct classification. Similarly for UAER, at the cut-point of 21.8 µg/min, there was 83.3% sensitivity and 91.3% specificity, allowing 89.7% correct classification.

Conclusions: The diagnostic performance of ACR and UAC in a spot as well as ACR and UAER in two-hour timed urine samples in patients with SCD is excellent. Healthcare professionals can confidently utilize these measures in this patient population.