Is there an M-spike in the globulin fraction of this sample?

On the electrophoresis service, you observe the following tracing. The urine protein concentration was 8 mg/dL (reference interval: =<10 mg/dL). What is your next action?

Answer: Look at the gel (see below, middle lane). The band-of-restricted mobility is not an M-spike but is an artifact where a dot of dye (for some reason) stained the gel. It is not appropriate to order an IFE in this situation unless there is clinical evidence to suggest that a monoclonal gammopathy is present.

Pseudo-M-spikes occur on SPEs when plasma is electrophoresed instead of serum. Such a pseudo-M-spike results from the presence of fibrinogen in the sample. Below is an example of such a pseudo-M-spike between the beta and gamma regions that was negative by IFE.

Is There an M-spike in the Globulin Fraction of This Sample?-3

A band-of-restricted mobility should only be termed an "M-spike" when it is proven that the band is a monoclonal immunoglobulin by IFE.

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Author bio

William E. Winter, MD and Roger L. Bertholf, PhD

Academy of Diagnostics & Laboratory Medicine Designation

Fellows of the Academy use the designation of FADLM. This designation is equivalent to FACB and FAACC, the previous designations used by fellows of the National Academy of Clinical Biochemistry and AACC Academy. Those groups were rebranded as Academy of Diagnostics & Laboratory Medicine in 2023.