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.
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.