Plasma pancreatic lipase activity: from analytical specificity to clinical efficiency for the diagnosis of acute pancreatitis

Abstract

Using five procedures (turbidimetry with the Boehringer Mannheim kit and with a home made reagent, reflectometry with the Eastman Kodak kit, colorimetry with the Sigma kit, and UV spectrophotometry with the Wako kit), lipase activity was assayed in the same group of 60 healthy adults and in 30 patients suffering from acute pancreatitis (n = 197 samples) as well as in a purified and stabilized preparation of human pancreatic lipase. Results indicated considerable inter-assay discrepancies for the mean values of the patients' results: catalytic activity concentrations differed by a factor of up to 16 according to the measurement procedures. For each method, mean patients' results were also expressed as multiples of the upper limit of normal values. This method of presentation did not significantly improve the intra-assay agreement, with maximal relative differences as high as 13-fold. When each method was calibrated with the same material (human pancreatic lipase), the inter-assay agreement was considerably improved. The causes of inter-assay disagreement are discussed in detail, and the necessity for a validated lipase calibrator is stressed, in order to improve the efficiency of the information transmitted by clinical laboratories to clinicians. A strategy is proposed, which includes development of a reference method and reference material, and a study of inter-assay commutability of secondary calibrators for a set of methods.