Cystatin C as a Determinant of Fasting Plasma Total Homocysteine Levels in Coronary Artery Disease Patients With Normal Serum Creatinine

Abstract

Abstract —Serum creatinine, a surrogate for both renal function and homocysteine generation, is a determinant of fasting plasma total homocysteine levels in coronary artery disease (CAD) patients. We hypothesized that among stable-CAD patients with normal creatinine levels (ie, ≤1.4 mg/dL), serum cystatin C, a more sensitive indicator of glomerular filtration rate, would better predict fasting total homocysteine levels in comparison with serum creatinine. Fasting plasma total homocysteine, folate, vitamin B 12 , and pyridoxal 5′-phosphate levels, along with serum cystatin C, creatinine, and albumin levels, were determined in 164 consecutive stable-CAD patients (mean±SD age, 61±9 years; 78.7% men) whose serum creatinine level was ≤1.4 mg/dL. All subjects were examined at least 3 to 4 months after the widespread availability of cereal grain flour products fortified with folic acid. General linear modeling with ANCOVA revealed that serum cystatin C ( P <0.001), B 12 ( P <0.001), age ( P =0.002), albumin ( P =0.008), and sex ( P =0.024) were independent determinants of fasting total homocysteine levels. Cystatin C alone determined over half of the variability (ie, R 2 ) in total homocysteine levels accounted for by these 5 independent regressors. In contrast, creatinine, folate, and pyridoxal 5′-phosphate were not independently predictive of fasting total homocysteine levels ( P >0.2). Consistent with the impact of folic acid fortification of cereal grain flour in the general population, only 1 of the CAD subjects (0.6%) had a plasma folate level <3 ng/mL. We conclude that serum cystatin C levels may reflect subtle decreases in renal function that independently predict fasting total homocysteine levels among stable-CAD patients with normal serum creatinine.