What is the best test to rule out possible multiple myeloma in a patient with amyloidosis?

In the context of ruling out multiple myeloma in a patient with amyloidosis, serum protein electrophoresis (SPEP) is considered the best initial test. This is because SPEP is designed to detect abnormal proteins in the blood, specifically monoclonal proteins (M-proteins) that are typically associated with multiple myeloma. The presence of these proteins can help indicate a myeloma diagnosis.

In patients with amyloidosis, especially those with light chain amyloidosis (AL amyloidosis), identifying these abnormal proteins is crucial as they can provide valuable insight into the underlying conditions contributing to the amyloid deposits. While a bone marrow biopsy is definitive for diagnosing multiple myeloma by looking for plasma cell infiltration, it is more invasive and is typically reserved for cases where the SPEP or other tests suggest possible myeloma.

Immunofixation electrophoresis offers a more sensitive method for detecting specific immunoglobulin light chains and can be used if the SPEP results are abnormal or inconclusive. Urine protein electrophoresis detects light chains (Bence Jones proteins) excreted in the urine, which can also be helpful, but it is not the first-line test for ruling out multiple my