In addition to a complete medical history and physical examination, the following is a list of common laboratory tests for the diagnosis of arthritis and other rheumatic diseases, according to the National Institute of Arthritis and Musculoskeletal and Skin Diseases, part of the National Institutes of Health:
- Antinuclear antibody. Measures blood levels of antibodies, which are often present in persons with rheumatic disease.
- Arthrocentesis (also called joint aspiration). Obtaining a sample of synovial fluid in the joint for examination by inserting a thin, hollow needle into the joint and removing the fluid with a syringe.
- Complement. Measures the level of complement, a group of proteins in the blood; low levels of complement in the blood are associated with lupus.
- Complete blood count. Measures the number of white blood cells, red blood cells, and platelets present in a sample of blood; a low white blood count (leukopenia), low red blood count (anemia), or low platelet count (thrombocytopenia) are associated with certain rheumatic diseases or the medications to treat them.
- Creatinine. A blood test to monitor for underlying kidney disease.
- Erythrocyte sedimentation rate (also called ESR or sed rate). A measurement of how quickly red blood cells fall to the bottom of a test tube. When swelling and inflammation are present, the blood's proteins clump together and become heavier than normal. Thus, when measured, they fall and settle faster at the bottom of the test tube. Generally, the faster the blood cells fall, the more severe the inflammation.
- Hematocrit (PCV, packed cell volume). Measures the number of red blood cells present in a sample of blood. Low levels of red blood cells (anemia) are common in people with inflammatory arthritis and rheumatic diseases.
- Rheumatoid factor. Detects whether rheumatoid factor is present in the blood (an antibody found in the blood of most, but not all, people who have rheumatoid arthritis, as well as other rheumatic diseases).
- Urinalysis. Laboratory examination of urine for various cells and chemicals, such as red blood cells, white blood cells, infection, or excessive protein; to indicate kidney disease associated with several rheumatic diseases.
- White blood cell count. Measures the number of white blood cells in the blood; increased levels of white blood cells may indicate an infection, while decreased levels may indicate certain rheumatic diseases or reaction to medication.
- C-reactive protein. A protein that is elevated when inflammation is found in the body. Although ESR and CRP reflect similar degrees of inflammation, sometimes one will be elevated when the other is not. This test may be repeated to test your response to medication.
- Uric acid. An indication of gout.
