Determination of α-Amylase Activity in Serum and Dialysate from Patients Using Icodextrin-Based Peritoneal Dialysis Fluid

Abstract

Objective Low serum activity of α-amylase has been reported in peritoneal dialysis (PD) patients following treatment with icodextrin-based peritoneal dialysis fluid (IPDF). However, these results have been questioned because icodextrin interferes with the polysaccharide reagent included in the assay as a substrate for α-amylase in the sample. Design We adapted a routine method using p-nitrophenol maltoheptaoside as substrate for the analysis of total α-amylase in serum and dialysate from 27 patients using IPDF. Serum from 12 healthy volunteers and serum and dialysate from 19 PD patients using glucose-based peritoneal dialysis fluid (GPDF) were used as controls. For the PD patients, time on dialysis ranged from 1 to 24 months (mean 5.7 months) and time of exposure to IPDF ranged from 1 to 52 weeks. Results To test for interference and recovery, and thus to validate the α-amylase assay, samples were spiked with IPDF and synthetic α-amylase. This revealed that addition of up to 75% IPDF did not interfere with the assay. Furthermore, α-amylase was fully recovered when spiked in serum from patients treated with IPDF. We show that total α-amylase activity is considerably lower in the serum of IPDF patients (20.3 ± 16.5 U/L, p < 0.001) than GPDF patients (85.5 ± 51.7 U/L) and healthy persons (55.1± 13.6 U/L). Conclusions We have shown that the IL method (IL Test; Instrumentation Laboratory, Lexington, MA, USA) measures α-amylase activity in samples containing icodextrin metabolites. The clinical significance of reduced plasma α-amylase activity, as well as the relative importance of pancreatic versus salivary and tissue-bound α-amylase, in PD patients using IPDF is not known.