Two Automated Fully Enzymatic Assays for Lipase Activity in Serum Compared: Positive Interference from Post-Heparin Lipase Activity

Abstract

The fully enzymatic Wako and Ektachem assays for pancreatic lipase in serum were found to yield precise (especially Ektachem) and consistent results that were significantly correlated (r = 0.995). Less good concordance was found with the turbidimetric aca method, results being on several occasions above normal by Wako or Ektachem but within the reference limit by the aca. Supplementation of aca packs with colipase generally increased lipase activities measured by the aca in these samples, thereby improving the correlation with Wako and Ektachem. In vitro addition experiments documented that both Wako and Ektachem were relatively insensitive to common chemical interferences. However, post-heparin lipase activities produced a positive interference in both assays, resulting in seemingly increased lipase activities that were suggestive of pancreatic disease. Substituting sodium glycocholate (6 mmol/L) for deoxycholic acid largely eliminated this positive interference in the Wako assay. Because Ektachem reagents cannot be modified in this way, we added sodium glycocholate (2-12 mmol/L) to sera; however, this failed to dissipate the in vivo effect of heparin on the Ektachem results.