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CRAB Criteria

Kathleen Colson, RN, BSN, BS, from the Jerome Lipper Multiple Myeloma Center at Dana-Farber Cancer Institute

Tip Sheet about this topic

Hello. I’m Kathleen Colson, and welcome to the Multiple Myeloma Center for Nurses video: CRAB Criteria. In this video, we will discuss the primary symptoms of multiple myeloma.

The most critical criteria in the diagnosis of symptomatic multiple myeloma is the evidence of multiple myeloma–related organ damage. The acronym CRAB is a mnemonic for the end-organ damage attributable to the underlying plasma cell proliferative disease. In addition to CRAB, infection is also a clinically significant symptom. The acronym CRAB stands for Calcium elevation, Renal dysfunction, Anemia, and Bone disease.

Multiple myeloma cells adhere to the stromal cells in the bone marrow. This adherence results in a dysregulation of cytokines that govern the bone remodeling process, leading to increased osteoclast activity and bone resorption. Increased bone resorption without new bone building can also lead to hypercalcemia, or elevated calcium in the blood. Symptoms of hypercalcemia include dry mouth, nausea, vomiting, anorexia, constipation, polydipsia, polyuria, fatigue, depression, confusion, and although rare, coma.

Renal impairment in multiple myeloma can be caused by several factors. The main cause of renal failure in patients is referred to as myeloma kidney. The term myeloma kidney, also called cast nephropathy, refers to light chain tubular damage. Another common cause of renal impairment is interstitial nephritis as a result of hypercalcemia. Dehydration is one possible consequence of calcium elevation, as is, in more severe cases, kidney failure. Myeloma protein kidney damage is asymptomatic at first, but a blood or urine test can reveal damage. As the kidneys begin to fail, they lose the ability to dispose of excess salt, fluid, and body waste products. This can lead to symptoms like weakness, shortness of breath, itching, and leg swelling.

Because myeloma cells replace normal blood-forming marrow cells, shortages of red blood cells, white blood cells, and blood platelets may occur, resulting in anemia, leukopenia, or thrombocytopenia, respectively. Anemia may cause weakness, reduced ability to exercise, shortness of breath, and dizziness. Having too few white blood cells, or leukopenia, lowers a patient’s ability to fight infections, such as pneumonia. And low platelet count, or thrombocytopenia, can cause even minor scrapes, cuts, or bruises to result in serious bleeding.

As you know, cells that form new bone are called osteoblasts; cells that break down old bone are called osteoclasts. Myeloma cells cause osteoclasts to accelerate bone destruction, while also interfering with osteoblasts receiving the signal to create new bone. As a result, old bone is broken down due to increased osteoclast activity without new bone to replace it due to decreased osteoblast activity. This can cause painful areas in the bone and lead to compression and pathologic fractures. The most common areas of fracture in patients with multiple myeloma are axial skeletal bones, such as vertebrae, ribs, pelvis, and extremities.

This concludes the CRAB Criteria video. To find out more on this and other topics related to multiple myeloma, please visit There you will also find a number of educational tools, including tip sheets to help you discuss these topics with your patients, answers to common questions, and other downloadable materials. Thank you.