What are the CRAB criteria?
The CRAB criteria are a group of features that play an important role in certain blood and bone marrow conditions, especially multiple myeloma. The word "CRAB" is an acronym that stands for the first letters of four medical terms: Calcium (high calcium levels in the blood), Renal failure (kidney problems), Anaemia (low red blood cells) and Bone lesions (bone damage). These four signs help doctors understand how serious a condition is and how urgently it needs to be treated.
What does each letter stand for?
Each letter in CRAB stands for a specific symptom or change in the body that can be linked to multiple myeloma or other plasma cell conditions.
C for Calcium: A calcium level that is too high in the blood, medically known as hypercalcaemia, can occur when bones break down and release large amounts of calcium. This can lead to symptoms such as tiredness, nausea, constipation, or even confusion.
R for Renal failure: This refers to reduced kidney function. When the kidneys are not working properly, the body has more difficulty removing waste products. This can show up as fluid retention, high blood pressure, or weakness.
A for Anaemia: Anaemia means there are too few red blood cells. This leads to less oxygen being carried around the body, which can cause tiredness, weakness, or shortness of breath.
B for Bone lesions: Bone damage or bone loss is typical of multiple myeloma. It can cause pain or increase the risk of bone fractures.
When do the CRAB criteria matter?
The CRAB criteria are used mainly when multiple myeloma is suspected. Multiple myeloma is a cancer of the bone marrow in which certain white blood cells, called plasma cells, multiply in an uncontrolled way. The CRAB criteria help to show whether the condition has already caused damage to organs or tissue, and whether immediate treatment is needed.
The CRAB criteria are also used in other conditions, such as certain early forms of multiple myeloma (for example MGUS or smouldering myeloma), to help decide whether and when treatment should begin.
What do the CRAB criteria mean for diagnosis?
If one or more of the CRAB criteria are found in a person, this suggests that the condition is no longer in an early stage and is already affecting the body. In this case, targeted treatment is usually necessary. If the CRAB criteria are absent, it may mean there is no immediate danger yet, and regular check-ups may be all that is needed for the time being.
A diagnosis is never based on the CRAB criteria alone. They are an important part of the picture, but are always looked at together with other lab results, imaging tests, and the overall situation.
Common concerns about the CRAB criteria
Many people who see the term CRAB criteria in a doctor's letter or medical report wonder how serious this is for them and what it means for the future. Finding one or more CRAB criteria is a sign that the condition is already having an effect on important organs. This can feel unsettling, but it is also an important signal that targeted treatment can and should now begin.
Not every abnormal blood result or finding on an X-ray automatically means that all four criteria are met. Values are often checked several times over a period of time to get a reliable picture. The CRAB criteria serve as a guide to help establish how urgent treatment is and whether it is needed.
What happens next if the CRAB criteria are met?
If one or more of the CRAB criteria are confirmed, targeted therapy is usually started. The exact treatment depends on the type and progression of the condition, as well as the person's general state of health. The aim is always to ease symptoms, protect organs, and slow the progression of the condition.
Various treatments are available for this, for example medicines that slow the growth of cancer cells, chemotherapy, antibody therapies, or in some cases a stem cell transplant. Additional measures may also be needed alongside these, such as stabilising the bones, treating the anaemia, or supporting kidney function.
Which treatment is right in each individual case is always decided on a personal basis. The CRAB criteria help to identify the need and urgency of treatment and to find the best possible time to begin.
