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If you’re living with multiple myeloma, your doctor may use a set of health signs called CRAB criteria to check how the disease is affecting your body. The CRAB criteria for multiple myeloma include high calcium levels, kidney problems, anemia, and bone damage.
These signs can help doctors diagnose active multiple myeloma, decide when treatment should start, and watch for signs of myeloma relapse.
Understanding the criteria can help you know which symptoms and test results matter and why your doctor may recommend treatment. Here’s what you need to know about the criteria, potential symptoms, and what they tell doctors about your condition.
CRAB criteria are signs and symptoms that can show myeloma cells are growing in the bone marrow. You might notice symptoms, or they may show up in laboratory tests.
Your doctor may order tests if you have symptoms that could be related to myeloma. Meeting one or more CRAB criteria may mean myeloma is affecting your organs.
Here’s what each of the four letters in the CRAB acronym stands for:
If you have blood calcium levels higher than 11 milligrams per deciliter, it may mean calcium is being released into your bloodstream from damaged bones.
You won’t know for sure that your blood calcium is high without a blood test, but you might have a few symptoms that point to high calcium. Symptoms of increased calcium in your blood include:
Kidney damage is the second CRAB criterion. It means the kidneys aren’t working as well as they should. In myeloma, kidney problems can happen when calcium levels in the blood are too high. They can also happen when antibodies called monoclonal proteins, or M-proteins, move from the blood into the urine.
Infections and other health problems can also make kidney damage worse.
Your doctor can check for kidney damage with blood and urine tests. These tests may measure electrolytes and serum creatinine. Your doctor may also request a 24-hour urine test to check your kidney function.
Your kidneys filter waste products from your blood, produce hormones, and balance fluids in your body. When your kidneys aren’t working properly, you may notice symptoms of myeloma kidney failure, such as:
Anemia is the third CRAB criterion. It means you have a low red blood cell count.
In multiple myeloma, anemia can happen when cancer cells in the bone marrow crowd out the cells that make healthy red blood cells. These cancer cells can also make it harder for the bone marrow to produce them.
Your doctor measures your blood hemoglobin levels to evaluate your red blood cell count. You may have anemia if your hemoglobin level is less than 10 grams per deciliter.
Fatigue and weakness are the two main symptoms that can happen when your red blood cell count is low. But you should also tell your doctor if you notice:
Multiple myeloma can cause bone damage because the cancer activates osteoclast cells. These cells break down older bone cells. Myeloma also blocks osteoblast cells, which build new bone. As a result, you lose bone mass faster than your body can replace it.
Multiple myeloma can result in osteoporosis, which causes weak and brittle bones that break easily. Myeloma bone disease can also involve osteolytic lesions, which are weak spots or holes in the bone.
Imaging tests like X-rays or magnetic resonance imaging (MRI) scans can show bone damage from myeloma. Your doctor might also evaluate bone damage by measuring clonal plasma cells in the bone marrow.
Bone pain can be a key indicator of bone damage from myeloma. Over time, bones can fracture or collapse, which can lead to complications like spinal compression and nerve damage. Osteoporosis and bone lesions cause bones to break much more easily than they typically would.
In 2014, researchers expanded the CRAB criteria by adding three more biomarkers to the list. These biomarkers are test results that can help doctors find signs of active myeloma before a person has symptoms from the original CRAB criteria.
SLiM-CRAB criteria may help doctors find signs of active myeloma earlier, including a possible relapse, so they can decide when to start treatment.
The “S” in SLiM stands for 60 percent bone marrow plasma cells (BMPC). Monoclonal plasma cells are abnormal plasma cells in myeloma that produce M-proteins.
Normally, there aren’t many plasma cells in bone marrow. If your bone marrow contains more than 60 percent BMPCs, it’s a sign you may have active multiple myeloma.
The “Li” in SLiM-CRAB represents your light chain ratio. Light chains are strands of proteins that are found on antibodies made by plasma cells.
Your doctor compares the number of involved light chains (light chains from myeloma cells) to the number of uninvolved light chains (light chains that don’t come from cancer cells) in your blood. They calculate a ratio using these numbers that helps them determine if your myeloma is active.
The final biomarker in the SLiM-CRAB criteria is bone marrow lesions found on an MRI scan. Two or more lesions in your bone marrow suggest active myeloma.
MRI scans work well for this compared to X-rays because they can show myeloma cells in the bone marrow before any bone fractures or osteoporosis have occurred. X-rays work better for showing bone damage that has already happened. By using an MRI scan, your doctor can detect active myeloma before any major bone damage occurs.
Myeloma specialists use the CRAB criteria to help diagnose myeloma and determine when a relapse may be happening. Based on biomarkers found during testing, they can decide when to recommend starting treatment for active myeloma.
CRAB features are most useful when symptoms have already appeared, which is why doctors now use SLiM-CRAB criteria. SLiM helps them determine if your myeloma is high-risk or about to progress.
Your doctor can use biomarker tests to check your risk of myeloma getting worse. These tests may show molecular changes in the body before major organ damage happens. To be diagnosed with active myeloma, you must meet both of these criteria:
Your doctor considers your biomarker test results to determine which type of myeloma you have and decides when to recommend treatment. Although myeloma doesn’t have a cure, starting treatment at the right time helps you maintain a good quality of life.
Treating myeloma too early can raise the risk that the disease may become resistant to treatment later on. But starting treatment too late can compromise your quality of life or lead to poor treatment outcomes.
Meeting any of the CRAB criteria could mean it’s time to consider treatment, usually starting with medications and a possible bone marrow transplant. Talk to your doctor about new treatment options for relapsed myeloma.
It’s important to communicate openly with your oncology care team. Let them know if you notice any new or worsening symptoms, even if you’ve been in remission for a long time. You can ask questions about myeloma symptoms, relapses, and treatment.
Your myeloma specialist might encourage you to get regular testing. Follow their instructions closely and stick to your monitoring schedule. Monitoring your biomarkers can help you recognize a relapse before it causes organ damage, so you can start treatment at the right time.
On MyMyelomaTeam, people share their experiences with multiple myeloma, get advice, and find support from others who understand.
Did CRAB symptoms or test results lead to your multiple myeloma treatment? Let others know in the comments below.
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