Improved Method for Estimating M-Spike Proteins in Serum Protein Electrophoresis

Abstract

Context: Serum monoclonal immunoglobulin (M-spike) in multiple myeloma is measured by gel electrophoresis (SPE) followed by densitometric scanning of the gel. The current standard methods delimit the M-spike component based on the projected gel image on screen (current standard method, CSM). However, the M-spike could also be selected by delimiting the peak(s) in the scanned curve (densitometry based method, DBM). Objective: The current study will correlate the results with these two approaches and to investigate which method may yield a result more close to the actual M-spike in the serum. Designs: Forty-one consecutive SPE files from 2010-2011 with positive M-spike were analyzed simultaneously with methods CSM and DBM. Serum monoclonal IgG from a myeloma patient with essentially no background polyclonal immunoglobulins was purified using protein G sepharose column and quantified using UV spectrophotometry. The measured concentration of purified IgG using methods CSM and DBM was compared to true IgG levels in spiked samples. Results: The measurements of 41 M-spikes using methods CSM and DBM correlated significantly (r=0.988, p<0.01). However, the measurement using method DBM was consistently higher than that using method CSM (49% ± 24%) In the measurement of purified monoclonal IgG, compared to method CSM, method DBM gave consistently closer results to the true IgG levels in spiked samples. Conclusions: The current method (CSM) underestimates the amount of serum M-spike. The revised method (DSB) based on the densitometric peak more accurately reflects serum M-spike levels using SPE.