American Board of Internal Medicine (ABIM) Certification Practice Exam

Which biomarker is commonly measured together with serum calcium and creatinine for MGUS evaluation?

1. Complete blood count

2. M protein level

3. β2-microglobulin

4. Lactate dehydrogenase

The correct answer is: M protein level

For the evaluation of monoclonal gammopathy of undetermined significance (MGUS), it is crucial to measure the M protein level alongside serum calcium and creatinine. The M protein is indicative of the presence and concentration of monoclonal immunoglobulin in the serum, which is a hallmark of MGUS. In the context of MGUS, serum calcium is measured to assess for possible hypercalcemia, which can occur if the monoclonal protein leads to bone resorption, while creatinine provides insight into renal function, as kidney damage can arise from the effects of the monoclonal protein. The M protein level serves as a critical component in characterizing the type and amount of monoclonal protein present, helping to determine the risk of progression to more serious conditions such as multiple myeloma. Measuring the M protein level allows clinicians to monitor the stability or progression of the condition. Overall, while other tests such as a complete blood count, β2-microglobulin, and lactate dehydrogenase can provide useful ancillary information in the broader context of hematological evaluation, they do not play the same direct role in the initial assessment and monitoring of MGUS as the M protein level does.