Objective: Patients with renal disease receiving dialysis therapy are susceptible to a deficit in ascorbic acid (AA) caused by loss during dialysis and a restricted dietary AA intake. In previous studies, in such patients, the methods generally used for AA determination are non-specific and insensitive, and control of the easily deteriorating AA in the samples is often disregarded. The purpose of this work was to study the AA plasma levels and dialyser clearances as well as the kinetics of administered AA in a group of dialysis patients, using selective and sensitive methodology and a procedure preserving the AA sample content.
Methods: Using an analytical method based on high-performance liquid chromatography and electrochemical detection, we have examined the dialyser clearance of AA as well as the pre- and post dialysis plasma levels of AA in patients on chronic dialysis therapy. The plasma AA levels were further measured after single and multiple dose supplementation of 200 mg p.o. per day.
Results: The majority of the patients (16 of 19) had pre-dialysis plasma levels below the normal range. The dialyser clearance of AA was 212 ml/min (median 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 uraemic whole blood and plasma was, on average, less stable than in samples from healthy subjects.
Conclusion: This study, using selective analytical method with adequate stability control, confirms that AA is readily removed by conventional haemodialysis membranes. Patients on chronic haemodialysis have remarkably low plasma AA levels unless given AA supplementation.