UNDERESTIMATION OF MONOCLONAL PROTEINS BY AGAROSE SERUM-PROTEIN ELECTROPHORESIS

The effect of serum dilution on monoclonal protein quantitation by ser um protein electrophoresis (SPE) on the agarose gel Paragon system was investigated in 388 serum samples from 106 patients with Ig G monoclo nal gammopathy. It was found that the pre-electrophoretic 1:5 serum di lution recommended by the manufacturer was adequate for some but not a ll sera, especially those with the highest M-protein concentrations. A s a result of the inadequate dilution, 232 (60 percent) of the 388 sam ples had M-protein concentrations that were significantly underestimat ed and the corresponding albumin concentrations overestimated. By Para gon SPE, the mean albumin concentration in these 232 sera was 41.8 (SD 6.7) g/L. After further dilution of these sera, the mean albumin conc entration was 36.7 (SD 6.8) g/L and was, in each case, always less tha n that in the corresponding 1:5 diluted serum. By the bromcresol green (BCG) dye-binding method, the albumin concentration was 34.9 (SD 4.3) g/L. Similarly, the M-protein concentration for 1:5 diluted sera was 51.9 (SD 12.9) g/L vs. 59.1 (SD 16.1) g/L for the further diluted sera , with the M-protein concentration in each further diluted sample alwa ys exceeding that in the corresponding 1:5 diluted serum. Underestimat ion of the M-protein concentration limits its clinical utilization in evaluating the patient's response to therapy and for early detection o f disease progression. A recommendation was made of a 1:10 dilution of sera that contain total protein from 91 g/L to 114 g/L and a 1:20 dil ution of sera in which the protein content is in the range of 115 g/L to 152 g/L to insure accurate estimation of protein fractions by Parag on SPE.