Early markers of renal dysfunction in patients with sickle cell/β-thalassemia

Progressive renal failure is one of the main complications in HbS/beta-thalassemia (HbS/beta-thal). Early identification of patients at high risk of developing renal failure is of great importance as it may allow specific measures to delay the progression of renal damage and thus reduce the incidence of end-stage renal failure and mortality. Early predictors of renal impairment in HbS/beta-thal remain to explore. Within this context, we studied 87 compound HbS/beta-thal patients (36 males/51 females; median age 39 years) and 30 healthy controls. In addition to conventional renal biochemistries we measured serum cystatin-C (Cys-C), urine N-acetyl-beta-D-glucosaminidase (NAG) excretion and serum and urinary beta(2)-microglobulin (beta(2)-M). Cystatin-C, NAG and serum beta(2)-M levels were higher in patients than controls. The incidence of patients with high levels of Cys-C, NAG, and beta(2)-M was 32.1, 74.7, and 70.1% respectively, while only 6.8% of patients had increased serum creatinine levels. Cystatin-C and serum beta(2)-M showed a strong correlation with creatinine clearance and age, while NAG positively correlated with proteinuria. An inverse correlation was also shown between hemoglobin and beta(2)-M, NAG, and Cys-C levels. Seven patients with proteinuria received therapy with angiotensin-converting enzyme (ACE) inhibitors. Changes of poteinuria positively correlated with NAG levels. These results indicate that Cys-C is an accurate marker of renal dysfunction, and urinary NAG excretion can be considered as a reliable index of the tubular toxicity, and possible predictor of proteinuria and eventual renal impairment in HbS/beta-thal patients. Furthermore, NAG measurement may be used for monitoring ACE-inhibitors therapy in HbS/beta-thal patients with proteinuria.