Total plasma homocysteine and related amino acids in end-stage renal disease (ESRD) patients measured by gas chromatography-mass spectrometry - Comparison with the Abbott IMx homocysteine assay and the HPLC method

Increased concentrations of homocysteine probably contribute to the high ca rdiovascular morbidity and mortality in hemodialysed end-stage renal diseas e (ESRD) patients and are determined by a variety of factors such as age, r esidual renal function, and vitamin status. Fasting plasma concentrations o f total homocysteine, methionine, cysteine, and cystathionine were determin ed by gas chromatography-mass spectrometry (GC-MS) in 131 ESRD patients rec eiving daily oral folate (160-320 mug) and vitamin B-6 (10-20 mg) supplemen ts. Concentrations of homocysteine determined by GC-MS were compared with t hose measured by high-performance liquid chromatography (HPLC) and an immun ofluorescence method (IMx analyzer) using Passing-Bablok regression analysi s. Mean plasma concentration of total homocysteine determined by GC-MS (28. 7 +/-1.9 mu mol/l [mean +/- SD]) was significantly lower than that determin ed by HPLC (34.0 +/- 04.5 mu mol/l; p<0.001) or IMx (32.4<plus/minus>03.9 m u mol/l; p<0.001). A close correlation existed between GC-MS and HPLC (r=0. 931; Y=1.203 x+0.279) and GC-MS and IMx (r=0.896; Y=1.105 x+0.766). Linear regression analysis showed positive correlations between plasma concentrati ons of homocysteine and cysteine (r=0.434; p<0.001) and homocysteine and cy stathionine (r=0.187; p=0.032). Plasma concentrations of homocysteine corre lated negatively with folate (r=-0.281; p=0.001) and vitamin B-12 (r=-0.229 ; p=0.009). GC-MS proved to be a sensitive and reliable method for the dete rmination of total plasma homocysteine and related amino acids. Despite vit amin supplementation, ESRD patients requiring chronic maintenance hemodialy sis, have high plasma concentrations of homocyst(e)ine which seems to be me tabolized mainly within the transsulfuration pathway, while remethylation t o methionine seems to be disturbed.