An Abnormal Case in Serum Glucose Measurement Due to Low Ionic Strength Condition of the Reagent Buffer

Abstract

We found a significant discrepancy in serum glucose measurement between colorimetric assay (automated chemical analyzer) with glucose oxidase (GOD) and GOD electrode assay (instant analyzer) in a 70-year-old male patient with macroglobulinemia. The difference was 3.33mmol/l of glucose. The patient had IgM proteinemia and the serum precipitated in low ionic strength buffer of the colorimetric assay. The precipitate caused a rapid increase in optic absorbance resulting in a higher glucose concentration reading than the true concentration. This type of discrepancy is estimated to occur in 0.15% of the measurements (n=2000, 95% confidence interval 0.03-0.44%). Avoiding reading of initial elevated absorbance due to precipitation by delayed reading in the colorimetric assay was effective in obtaining reasonable measurement. We recommend laboratory analysts to find the best analytic condition.