Carnitine deficiency is highly prevalent among hemodialysis patients due to the decreased biosynthesis of carnitine in injured kidney tissue and its removal by dialysis therapy. Many studies have reported that carnitine deficiency is significantly associated with various uremia-related complications, including erythropoietin-resistant anemia, left ventricular dysfunction, and muscular cramps. In this cross-sectional study, we evaluated the current status of altered carnitine metabolism in outpatients on regular hemodialysis who had been enrolled in a prospective observational study investigating the efficacy of intravenous carnitine administration. We assessed factors contributing to serum-free carnitine concentrations (F) and the serum acylcarnitine concentrations/serum-free carnitine concentrations ratio (A/F), known indices of carnitine metabolism, in a total of 501 patients in Showa University Northern Yokohama Hospital and its affiliated hospitals. The prevalence of the deficient group (F<20µmol/l) was only 8.4%. The percentage of patients who had A/F>0.4µmol/l was as high as 98.8%. These facts suggested that nearly all patients receiving regular hemodialysis had altered carnitine metabolism. Multivariable analysis demonstrated that the following were significantly associated with a lower F: female, longer hemodialysis, and higher normalized protein catabolic rate (nPCR). On the contrary, female, longer hemodialysis, lower levels of serum albumin and phosphate, and higher nPCR were significantly associated with a higher A/F. In conclusion, we found that the prevalence of carnitine disorder was extremely high among outpatients on regular hemodialysis, and that nPCR and SUN, which are nutritional parameters, were significantly associated with F or A/F. However, the association between those nutritional parameters and carnitine disorder was paradoxical in the present study, although the reason for this remains uncertain. Further investigations are necessary to elucidate the pathophysiology of carnitine disorder among dialysis patients.
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