Version July 2025
CBC: complete blood count; CRAB: hypercalcemia, renal insufficiency, anemia, or bone lesions; CT: computed tomography; FLC: free light chain; M protein: monoclonal protein; MM: multiple myeloma; MRI: magnetic resonance imaging; SMM: smoldering multiple myeloma; SPEP: serum protein electrophoresis; UPEP: urine protein electrophoresis.
* CRAB criteria refers to end-organ damage (hypercalcemia, kidney impairment, anemia, or bone lesions) felt to be related to the underlying plasma cell proliferative disorder. To evaluate for bone lesions, whole body low dose CT is the preferred initial test. One or more osteolytic lesions ≥5 mm in size on CT is diagnostic of MM. Involved/uninvolved FLC ratio of 100 or more is also diagnostic of MM provided the absolute involved FLC level is at least 100 mg/L. Bone marrow plasma cells ≥60% is also diagnostic of MM.
¶ We follow these patients with clinical examination and laboratory testing (SPEP, UPEP, urine immunofixation, CBC, creatinine, calcium, and FLC ratio) after 2 to 3 months. If stable, we repeat these studies every 4 to 6 months for one year, then every 6 to 12 months. Follow-up imaging is performed every year if no abnormality was seen on prior imaging studies, and every 6 months if one focal lesion was seen on prior MRI.
