Characteristics of AMY values among substrates (G2 and G7) of amylase assay regents and samples with large discrepancies in their measured values

Abstract

[Introduction] α-Amylase (AMY) is essential for diagnosing salivary gland and pancreatic diseases. During our correlation test using Gal-G₂-CNP and Et-G₇-pNP methods, we found significant discrepancies in AMY values for a specific sample. Therefore, we investigated substrate characteristics in the AMY measurement reagents and the reasons for discrepancy in the specific sample. [Method] We evaluated AMY and P-AMY measurement reagents, assessing reactivity differences due to isozyme variations and α-Glucosidase inhibitor effects between substrates. Moreover, the sample with significant discrepancies underwent PEG treatment. [Results] The correlations were strong for AMY. When the divergence rate was categorized into three groups, decreasing P-AMY proportion significantly increased the deviation rate between Gal-G₂-CNP and Et-G₇-pNP (p < 0.001). The α-Glucosidase inhibitors had no observed effect on the substrates (p = 0.703). The significant discrepancies sample had undergone PEG treatment, and suggesting macro-AMY as a possible cause. [Discussion] The AMY and the P-AMY reagents for Gal-G₂-CNP and Et-G₇-pNP showed strong correlations and yielded good results. However, AMY reactivity between substrates varied with P-AMY proportion. PEG treatment suggested macro-AMY as a possible cause for the divergence, but did not clarify the underlying reason for such significant deviation. In the future in Japan, as standardized methods for AMY become more prevalent, the likelihood of clinical discrepancies like this one is expected to decrease.