Blood tests can help diagnose arthritis, monitor treatments, and track disease activity.
Laboratory blood tests are valuable diagnostic tools. They are usually not definitive when considered alone. The entire clinical picture of a patient, and the patient's history must be evaluated along with laboratory test results in order to produce an accurate diagnosis.
- Lab Tests - Test Your Knowledge
- Do Normal Blood Test Results Rule Out Rheumatic Diseases?
- What Blood Tests Are Commonly Ordered to Diagnose and Monitor Arthritis?
Part 1 - General Blood Tests
Part 2 - Specialized Blood Tests
- Erythrocyte Sedimentation Rate (ESR or Sedrate)
- Rheumatoid Factor (RF)
- HLA B27 Typing
- Antinuclear Antibody (ANA)
- C-Reactive Protein (CRP)
- Lupus Erythematosus (LE) Test
- Anti-DNA and Anti-Sm
Complete Blood Count (CBC)
The complete blood count is a test of red blood cells, white blood cells, and platelets. Blood consists of these components suspended in a thick, colorless fluid called plasma. Automated machines rapidly count the cell types.
The white cell count is normally between 5,000-10,000. Increased values suggest inflammation or infection.
Such things as exercise, cold, and stress can temporarily elevate the white cell count.
Normal values for the red cell count vary with gender.
- Males normally have values around 5-6 million per microliter.
- Females have a lower normal range at 3.6-5.6 million red cells per microliter.
Hemoglobin / Hematocrit
Hemoglobin, the iron containing component of red cells which carries oxygen, is also measured in a complete blood count. The normal hemoglobin value for males is 13-18 g/dl. Normal for females is 12-16 g/dl. The hematocrit measures the percent of total blood volume which is red cells. Normal value for males is 40-55%, and the normal value for females is 36-48%. Generally, the hemoglobin times 3 equals the hematocrit. Decreased values are indicative of anemia.
The MCV, MCH, MCHC are red cell indices which indicate the size and hemoglobin content of individual red cells. These indices give clues as to the probable cause of an existing anemia.
Platelets are components which are important in clot formation. Many medications used in the treatment of arthritis can decrease the platelet count or affect platelet function. Normal values range from 150,000-400,000.
The percent and absolute number of each type of white blood cell is called the differential.
- Neutrophils are increased in bacterial infections and acute inflammation.
- Lymphocytes are increased in viral infections.
- Monocytes are increased in chronic infections and eosinphils are increased in allergies.
- Basophils, which are generally 1 or 2% do not usually increase.
The process of inflammation can cause changes in the blood count. The red cell count may go down, the white cell count may go up, and the platelet count may be elevated. While anemia may accompany inflammatory arthritis it may be caused by other things such as blood loss or iron deficiency. Only when other causes have been ruled out can a doctor interpret blood abnormalities as a sign of inflammation.
The chemistry panels are a series of tests which are used to evaluate overall health. For example, according to A.D.A.M., "the CHEM-20 is a group of 20 chemical tests performed on serum (the portion of blood without cells). Electrolytes are ionized salts in blood or tissue fluids (ions are atoms or molecules that carry an electrical charge). Electrolytes in the body include sodium, potassium, chloride, and many others."
The tests also include heart risk indicators, diabetes indicators, as well as tests for:
- kidney function
- liver function
- thyroid function
For example, a patient with a high creatinine level may have a problem with the kidneys. Creatinine is a waste product found in the blood. Certain types of inflammatory arthritis can affect kidney function. Certain arthritis drugs can affect kidney function too. Uric acid is another test of the blood chemistry panel which, if elevated, may be indicative of gout.