Determinants of fasting plasma total homocysteine levels among chronic stable renal transplant recipients

Background. Although several studies have demonstrated an unadjusted association between folate status and fasting plasma total homocysteine (tHcy) levels among renal transplant recipients, no data confirming the strength or independence of this association have been reported. Methods. We determined fasting plasma folate, B-12, and pyridoxal 5'-phosphate (active vitamin B-6) levels, along with other potential determinants of plasma tHcy levels (i.e., age, sex, creatinine levels, and Cockcroft-Gault estimated creatinine clearance, current immunosuppressive regimen, and history of clinical cardiovascular disease), among 86 renal transplant recipients. The recipients were greater than or equal to 6 months after transplantation, lived in the Providence, Rhode Island metropolitan area, and were examined between February and June 1998. Results. Stepwise general linear modeling with analysis of covariance revealed that only creatinine level, age, and vitamin status were independent regressors (i.e., P<0.100) of tHcy levels. Moreover, creatinine level alone determined most of the variability in tHcy levels (i.e., R-2) accounted for by these independent variables (R-2=0.416 for creatinine level alone; total R-2=0.575). In contrast, the R-2 for folate alone was only 0.046, and even for all three B vitamins combined, the R-2 was just 0.088. Conclusions. We conclude that renal function is the overriding independent determinant of fasting tHcy levels among stable renal transplant recipients. In comparison to renal function, vitamin status has a relatively marginal influence on tHcy levels and cyclosporine use has essentially none at all.