Comparison of renal function markers in Kuwaiti patients with sickle cell disease

Background: Proteinuria is a common manifestation of renal disease which is a significant cause of morbidity in patients with sickle cell disease (SCD). Objective: To evaluate and compare cystatin C, beta(2)-microglobulin, and creatinine as markers of renal disease in relation to the degree of proteinuria and other complications of SCD. Methods: 24 h urine collections were used for estimation of urine protein and creatinine clearance in 59 patients with SCD. Results were correlated with plasma cystatin C, beta(2)-microglobulin, creatinine, glomerular filtration rate (GFR; derived from plasma creatinine by Cockcroft-Gault, MDRD formulae, and calculated cystatin C clearance), and clinical and haematological variables. Results: Comparing the different methods of GFR, the proportion of patients with hyperfiltration (GFR>140 ml/min) were 30.5% (MDRD), 44.1% (Cockcroft-Gault), and 10.2% (calculated cystatin C clearance). Cystatin C was the most consistent marker of hyperfiltration. The endogenous markers of GFR showed an increasing trend with increasing proteinuria, but haematological variables were not correlated with cystatin C, beta(2)-microglobulin, or plasma creatinine. Urine protein excretion was correlated with age (r=0.33) and significant proteinuria was present in 13.6% of patients. Patients with proteinuria had lower haemoglobin concentration (p=0.027) than those without proteinuria but HbF was not related to the degree of proteinuria or to markers of GFR. Conclusions: Markers of GFR show variable ability to identify hyperfiltration in patients with SCD, but cystatin C is the best endogenous marker. Proteinuria is associated with age, haemoglobin, and abnormalities of GFR. Routine screening is recommended to allow for early detection and intervention.