What laboratory finding is characteristic of multiple myeloma?

The characteristic laboratory finding in multiple myeloma is the increased serum monoclonal protein, often referred to as M-protein. In this condition, there is a proliferation of abnormal plasma cells in the bone marrow that produce large amounts of a single type of immunoglobulin or its subunit. This results in elevated levels of monoclonal antibodies in the serum, which can be detected using serum protein electrophoresis.

The presence of M-protein is pivotal not only for diagnosing multiple myeloma but also for monitoring disease progression and response to treatment. It serves as a hallmark of this malignancy, as the overproduction of these paraproteins can lead to various complications such as renal impairment, hypercalcemia, and bone lesions, all of which are commonly associated with multiple myeloma.

Other options may be present in multiple myeloma but are not as definitive. For example, while decreased hemoglobin levels can occur due to bone marrow infiltration or the effect of abnormal proteins, they are not uniquely characteristic of multiple myeloma. Elevated white blood cell count can happen but is not specific to this condition, as various infections or inflammatory processes can also lead to leukocytosis. The presence of immature granulocytes generally indicates a response to infection