Evaluation of a new assay for pancreatic amylase: performance characteristics and estimation of reference intervals

We have evaluated a new assay for the specific determination of pancreatic (P) isoamylase, the principle being based on a synergistic inhibitory effect of two monoclonal antibodies directed towards salivary (S) amylase. After 3 min incubation, activities were determined with maltoheptaoside-PNP as substrate on a Hitachi 705 analyzer at 25, 30 and 37 degrees C, respectively. Coefficients of variation ranged from 0.6 to 5.4% for within-run and 2.1 to 9.9% for day-to-day precision. Linearity held up to 1200 U/L (25 degrees C) and 2300 U/L (37 degrees C). Comparison of the new method with the wheat germ inhibitor technique showed an excellent correlation, with coefficients ranging from 0.990 to 1.00. Using purified P- and S-amylase we observed no inhibiting cross-reactivity of the antibodies with the P-isoenzyme, but an incomplete blockage of S-amylase: residual activity was approximately 2% at 25 and 30 degrees C, and 2.5% at 37 degrees C. The distribution pattern of P-, S- and total amylase activity in serum of healthy subjects was only slightly skewed to the right. We found neither an influence of sex nor of age on the reference ranges. In random urine samples, distribution of activities was strongly skewed. However, if the activity was related to the urinary creatinine concentration, an approximately normal distribution was obtained, allowing, as in serum, the establishment of upper and lower reference values.