American Board of Internal Medicine (ABIM) Certification Practice Exam

Which factor increases the risk of progression from monoclonal gammopathy of undetermined significance to multiple myeloma?

1. IgG M protein

2. M protein level of at least 1.5 g/dL

3. Normal serum free light chain ratio

4. Age above 60

The correct answer is: M protein level of at least 1.5 g/dL

The progression from monoclonal gammopathy of undetermined significance (MGUS) to multiple myeloma is influenced by several factors, one of which is the M protein level. A specific threshold of M protein level, particularly at least 1.5 g/dL, indicates a higher risk for progression. In clinical practice, MGUS is characterized by the presence of a monoclonal protein in the serum without other features of multiple myeloma. However, as the M protein level increases, it suggests a greater burden of clonal plasma cells, elevating the risk of transformation into multiple myeloma. Research indicates that an M protein level of 1.5 g/dL or higher is associated with a significantly increased risk of progression compared to lower levels. Other factors, such as the type of monoclonal protein (for instance, IgG versus IgA) or age, also contribute to risk assessments, but a level of at least 1.5 g/dL is a specific clinical marker that correlates strongly with the likelihood of progression to multiple myeloma, making it a critical factor in monitoring and management of patients with MGUS.