Association of haptoglobin phenotypes with markers of diabetic nephropathy in Type 2 diabetes mellitus

Background: Recent studies have suggested an inheritable influence of haptoglobin phenotypes on the development of microalbuminuria in diabetic patients. In this study, we aimed to investigate whether microalbuminuria and serum levels of Cystatin C (Cys C) were correlated with haptoglobin phenotypes in patients with Type 2 diabetes mellitus. Methods: Fasting blood samples and first morning urine specimens were collected from 216 patients with type 2 diabetes (mean age 60.8 +/- 6.8) and from 108 healthy controls (mean age 59.3 +/- 6.5 years). Serum was used for the determination of Cys C, creatinine, and haptoglobin (Hp) phenotypes, while urine specimens were used for the determination of microalbuminuria. Microalbuminuria was expressed as albumin (mg)/creatinine (g) ratio [ACR (mg/g)], and patients were divided into three groups according to the values of ACR: normoalbuminuria ( <30), microalbuminuria (30-300) and macroalbuminuria ( > 300). Results: Irrespective of Hp phenotypes, Cys C, but not creatinine, was significantly higher in patients than that in controls. According to haptoglobin phenotypes, however, the levels of Cys C, duration of diabetes, and age, were significantly higher in patients with Hp1-1 phenotype than that in patients with the other phenotypes. Moreover, micro- and/or macroalbuminuria were present in all diabetic patients, with no significant difference in frequency of occurrence among the three Hp phenotypes. Multiple linear regression revealed that duration of diabetes and age of patient were significant predictors of Cys C (P < .0001), whereas creatinine associated with age only (P = .016). Logistic regression analysis showed that duration of diabetes [P <= .0001; odds ratio (OR) = 1.678, 95% CI = 1.43-1.97], and age (P = .0004; OR = 0.847, 95% CI = 0.77-0.93), significantly associated with micro- and/or macroalbuminuria. Hp phenotypes however, were not associated with any marker of kidney function. Conclusion: Findings from this study demonstrate no association between Hp phenotypes and markers of diabetic nephropathy. Markers of diabetic nephropathy however, are greatly influenced by duration of diabetes and age of patients. (C) 2008 Elsevier Inc. All rights reserved.