A complete blood count, which includes hemoglobin, hematocrit, white blood cell count, differential (what types of white blood cells are present), and platelet count, is one of the most common baseline tests ordered in an arthritis clinic. It is used for diagnosis and monitoring of medications and is also used to detect blood disorders such as anemia.
Understanding the cause of anemia in a patient with arthritis is important to providing appropriate treatment. For instance anemia can be due to abnormal destruction of red blood cells due to antibodies directed against the red blood cells. This phenomenon is occasionally seen in diseases like systemic lupus erythematosus (SLE). Low white blood cells counts and low platelet counts can also be seen in SLE.
Many types of inflammatory arthritis such as rheumatoid arthritis, SLE, etc. , are associated with an anemia called the “anemia of chronic disease. " This type of anemia does not respond to iron. Red blood cells are normal size and normal color. The anemia is due to inflammation which “locks" the iron inside the bone marrow and prevents it from being used to make new red blood cells. The treatment for this anemia is better control of the arthritis.
Contrast that with the anemia from iron deficiency. This can be seen in patients treated with non-steroidal anti-inflammatory drugs (NSAIDS) who develop gastrointestinal bleeding. The anemia is caused by loss of blood and will respond to iron therapy. Red blood cells are small and pale.
Therapy with drugs such as methotrexate can lead to a deficiency of folate. This folate deficiency also causes an anemia. The anemia in this case is associated with large red blood cells. It is a sign that the patient needs to be treated with folic acid. Azathioprine is another drug used for arthritis that causes an anemia with large red blood cells.
Anemia should be investigated to determine whether the anemia is due to drug toxicity, complications of the arthritis, or some other cause. For example, a patient with large red blood cells may have a vitamin B12 deficiency accounting for their anemia.
Patients with anemia may complain of being fatigued or of feeling weak.
Patients with low platelet counts may be an increased risk for developing severe bleeding.
Patients with low white blood cell counts may be at increased risk for infections.
The presence of anemia or other blood abnormality will be an important determinant of the course of action needed to treat the patient and their arthritis.
Patient receiving arthritis medicines are at increased risk for developing different side effects. As a result they need to be monitored carefully.
Nathan Wei, MD, FACP, FACR is a rheumatologist and Director of the Arthritis and Osteoporosis Center of Maryland (http://www.aocm.org ). He is a Clinical Assistant Professor of Medicine at the University of Maryland School of Medicine and consultant to the National Institutes of Health. For more info: Types of Arthritis