Other Diagnostic Tests
There are other less commonly ordered tests that may be necessary for some patients. These are usually ordered to confirm a diagnosis or check for adverse effects of treatment.
Blood Profiles and Urine Tests
Kidney profiles and liver profiles (blood tests) are sometimes ordered to check that medications you may be taking are not damaging or impairing the normal function of those organs.
Blood tests that are done to test for kidney damage include BUN or blood urea nitrogen (normal is 7–20 mg/dl) and serum creatinine (normal is 0.8–1.2 mg/dl for males and 0.6–0.9 mg/dl for females).
Urine tests are also used to check for kidney damage. These tests include urinalysis (includes many parameters), urea clearance (normal is 64–99 ml/min), and creatinine clearance (normal for adults under forty years old is 90–139 ml/min for males and 80–125 ml/min for females). For adults over forty years old, the normal decreases 6.5ml/min for each decade. There is also the urine osmolality (normal is 50–1400 mOsm/kg for random specimen) and a 24-hour urine protein test (normal is less than or equal to 150 mg of protein).
Liver enzymes are also analyzed to check for side effects of arthritis medications. These include AST (SGOT) with a normal range of 10–34 IU/L (international units per liter), ALT (SGPT) with a normal range of 5–35 IU/L, ALP with a normal range of 20–140 IU/L, and GGT or GGTP with a normal range of 0–51 IU/L.
Bilirubin, albumin, total protein, and prothrombin time are also tests helpful in determining liver function.
Biopsies are ordered to confirm a diagnosis or assess disease activity. A biopsy involves the removal of a small piece of tissue that is then prepared for microscopic examination. Biopsies of the skin, muscle, and kidney are the most commonly performed biopsies for arthritis patients.
For arthritis patients, skin biopsies are used to diagnose lupus, vasculitis, psoriatic arthritis, or other types of arthritis that have skin involvement. Muscle biopsies are used to diagnose polymyositis or vasculitis. Kidney biopsies help diagnose lupus. Liver biopsies are used to check for damage in patients taking methotrexate. Biopsy of minor salivary glands in the mouth is helpful in confirming a diagnosis of Sjögren's syndrome, and biopsy of the synovial lining of a joint helps rule out an indolent infection such as tuberculosis or fungus.
Other Imaging Techniques
There are more highly specialized imaging techniques available, such as arthrography, which involves injecting dye into your joint so more details are visible on the x-ray.
An isotope bone scan involves a small amount of radioactive isotope injected into your blood. The isotope is taken up by your bones and gives off gamma rays. After a special camera detects the gamma rays, a computer receives the information and builds an image that shows where bones are inflamed.
CT scans use x-rays which record images of sections of the body. A computer creates cross-sectional pictures from the information. Detailed pictures of the skeleton as well as muscles and other tissues are created. CT scans transmit a much larger amount of radiation than plain radiographs.
DEXA (dual energy x-ray absorptiometry) scans are used to evaluate bone density and are primarily used to diagnose osteoporosis, a condition of bone thinning. Radiation is minimal for DEXA scans.
Ultrasound uses high frequency sound waves to create pictures. It is useful for locating the abnormal presence of fluid around joints and tendons.