Plasma ascorbic acid in patients undergoing chronic haemodialysis

Objective: Patients with renal disease receiving dialysis therapy are susce ptible to a deficit in ascorbic acid (AA) caused by loss during dialysis an d a restricted dietary AA intake. In previous studies, in such patients, th e methods generally used for AA determination are non-specific and insensit ive, and control of the easily deteriorating AA in the samples is often dis regarded. The purpose of this work was to study the AA plasma levels and di alyser clearances as well as the kinetics of administered AA in a group of dialysis patients, using selective and sensitive methodology and a procedur e preserving the AA sample content. Methods: Using an analytical method based on highperformance liquid chromat ography and electrochemical detection, we have examined the dialyser cleara nce of AA as well as the pre- and post dialysis plasma levels of AA in pati ents on chronic dialysis therapy. The plasma AA levels were further measure d after single and multiple dose supplementation of 200 mg p.o, per day. Results: The majority of the patients (16 of 19) had predialysis plasma lev els below the normal range. The dialyser clearance of AA was 212 ml/min (me dian value). Following dialysis, the plasma AA concentrations were reduced by a median of 33%. AA supplementation significantly increased these levels ; however, they dropped soon after supplementation was stopped. AA in uraem ic whole blood and plasma was, on average, less stable than in samples from healthy subjects. Conclusion: This study, using selective analytical method with adequate sta bility control, confirms that AA is readily removed by conventional haemodi alysis membranes. Patients on chronic haemodialysis have remarkably low pla sma AA levels unless given AA supplementation.