Trial of M-protein screening method using an automatic analyzer

Abstract

Patients with monoclonal immunoglobulin (M-protein) have an extremely high proportion of M-protein in their serum, significantly reducing the levels of other immunoglobulins. In contrast, non-M-protein patients have a more balanced distribution of various proteins. Proteins can either dissolve or precipitate when added to a salt solution, depending on the concentration. When patient serum was reacted with two solutions of different salt concentrations (purified water and phosphate-buffered saline), the absorbance changes were significantly different between M-protein and non-M-protein patients. Therefore, we investigated the optimal photometric wavelengths, volumes, and photometric points for M-protein screening based on these absorbance changes. The results showed that the optimal wavelength was 340 nm, the reagent volume was 80 μL, the patient serum volume was 16 μL, and the photometric point was 1. We subsequently evaluated the performance of this test method. For correlation, significant differences were observed in protein electrophoresis (presence or absence of an M-peak). For concomitant accuracy, the coefficient of variation (CV%) was 4.2% at an absorbance change of around 0.064. In terms of Randomized two-time measurement method, there was a strong correlation between the measurements of the two groups. For criterion validity, the cutoff value was set at 0.048 (sensitivity 67.7%, specificity 59.1%) based on the receiver operating characteristic (ROC) curve obtained from logistic regression analysis. The area under the curve was significantly higher with this test method than with the ROC curve for age, total protein levels, albumin levels, and A/G ratio alone. Therefore, this test is useful for M-protein screening.