title: Determination of alpha-amylase activity in serum and dialysate from patients using icodextrin-based peritoneal dialysis fluid.
abstract: OBJECTIVE
  Low serum activity of alpha-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 alpha-amylase in the sample.
  
  
  METHODS
  We adapted a routine method using p-nitrophenol maltoheptaoside as substrate for the analysis of total alpha-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 alpha-amylase assay, samples were spiked with IPDF and synthetic alpha-amylase. This revealed that addition of up to 75% IPDF did not interfere with the assay. Furthermore, alpha-amylase was fully recovered when spiked in serum from patients treated with IPDF. We show that total alpha-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 (ILTest; Instrumentation Laboratory, Lexington, MA, USA) measures alpha-amylase activity in samples containing icodextrin metabolites. The clinical significance of reduced plasma alpha-amylase activity, as well as the relative importance of pancreatic versus salivary and tissue-bound alpha-amylase, in PD patients using IPDF is not known.
authors.affiliation: Division of Renal Medicine, Department of Clinical Science, Huddinge University Hospital, Karolinska Institutet, Stockholm, Sweden. bjorn.anderstam@klinvet.ki.se
authors.forename: Björn
authors.initials: B
authors.lastname: Anderstam
authors.forename: Elvia
authors.initials: E
authors.lastname: García-López
authors.forename: Olof
authors.initials: O
authors.lastname: Heimbürger
authors.forename: Bengt
authors.initials: B
authors.lastname: Lindholm
mesh_terms: D000368:Aged; D000893:Anti-Inflammatory Agents / Q000032:analysis* / Q000097:blood*; D015314:Dialysis Solutions / Q000737:chemistry* / Q000494:pharmacology / Q000627:therapeutic use*; D005260:Female; D005936:Glucans / Q000737:chemistry* / Q000494:pharmacology / Q000627:therapeutic use*; D005947:Glucose / Q000737:chemistry* / Q000494:pharmacology / Q000627:therapeutic use*; D006801:Humans; D000077607:Icodextrin; D007674:Kidney Diseases / Q000097:blood* / Q000201:enzymology / Q000628:therapy*; D008297:Male; D008875:Middle Aged; D010530:Peritoneal Dialysis; D015203:Reproducibility of Results; D013997:Time Factors; D000516:alpha-Amylases / Q000032:analysis* / Q000097:blood* / Q000187:drug effects
chemical_list: D000893:Anti-Inflammatory Agents; D015314:Dialysis Solutions; D005936:Glucans; D000077607:Icodextrin; D000516:alpha-Amylases; D005947:Glucose