<qa>  What is the value of urine M-protein?- Serum and urine M-protein levels should be determined by electrophoresis rather than by quantitative immunoglobulin Ig measurement. Exceptions are made in cases in which the M-spike value may be deemed to be unreliable e.g. co-migrating M-spike. In these cases, quantitative Ig should be used. To assess response and progression, however, SPEP values should only be compared to SPEP values and quantitative Ig values only to quantitative Ig values. 