In a case where a patient has been found with an IgMκ paraprotein, what is a critical initial test to perform?

The identification of an IgMκ paraprotein indicates the presence of an abnormal monoclonal protein, which is often associated with conditions such as multiple myeloma or Waldenström's macroglobulinemia. Performing serum protein electrophoresis is essential as it allows for the separation of the different proteins in the serum based on their size and charge. This technique will facilitate the visualization of the monoclonal band that corresponds to the IgMκ paraprotein, providing critical information regarding the level and characteristics of the paraprotein.

This test is particularly useful in determining the overall immunoglobulin status of the patient and assessing the degree of paraprotein present. Following this initial assessment, further tests, including urine protein electrophoresis and immunoglobulin quantification, may be warranted based on the findings from the serum protein electrophoresis. This prioritization is crucial for the accurate diagnosis and subsequent management of the underlying plasma cell disorder.