Making a Back Pain Diagnosis: Blood Tests

Generally, blood tests are not among the medical tests ordered by doctors in the diagnosis of back pain, though they may be appropriate if the doctor suspects certain diseases of blood disorders causing the back pain symptoms. In some cases, certain blood tests can assist the diagnostic process by helping doctors differentiate medical from mechanical causes of back pain. Blood tests that may be used to diagnose medical causes of back pain include:

Tissue Typing: There are several forms Spondylarthropathy (arthritis that affects the spine), including psoriatic arthritis, reactive arthritis, and ankylosing spondylitis. These three forms or arthritis may affect the joints of the spine, causing back pain, as well as other joints in the musculoskeletal system. A blood tests that comes back positive for the specific genetic marker called HLA-B27 indicates ankylosing spondylitis or one of the other spondyloarthropathies. Ankylosing spondylitis is a form of arthritis, associated with autoimmune dysfunction, that primarily affects the sacroiliac and spinal joints). A positive indication of the HLA-B27 gene through blood testing may also indicate reactive arthritis (a similar disease characterized by inflammation of the urethra, eyes, and joints). Some people may have the a positive indication HLA-B27 genotype, but not some of the phenotypes, such as inflammation in the joints and other tissues. For this reason, a blood test alone does not lead to a definitive diagnosis of spondyloarthropathies such as ankylosing spondylitis. Additional testing such as medical imaging of the joints affected may provide doctors with a more definitive diagnosis.

Erythrocyte sedimentation rate ("sed rate" or ESR): A Erythrocyte sedimentation rate blood test is used to detect and measure inflammation. The ESR is the rate at which red blood cells sediment in a period of 1 hour. Erythrocytes are red blood cells - they are the blood cells that deliver oxygen to the body tissues and return carbon dioxide to the lungs to be expelled when breathing. To perform the test, blood is drawn from the patient and collected into a test tube, where the force of gravity will cause the red blood cells to collect at the bottom of the tube, and the clear blood serum to collect at the top of the tube. The rate at which the blood's individual components will be a non-specific measure of inflammation. The higher the sedimentation rate (sed rate), the more inflammation is present. A high sed rate may point to a number of inflammatory diseases that cause arthritis, and to other medical problems such as infection polycythemia, and in rare cases, tumors or cancer.

Complete blood count (CBC): A Complete blood count (CBC) is a test on the blood that shows the levels of the different types of blood cells. A complete blood count will show the concentrations of the following components of blood: Hemoglobin (Hgb), white blood cells (WBC), platelets (Plt), and Hematocrit (Hct). Changes in blood cell levels could indicate medical conditions such as infection or inflammatory disease, such as ankylosing spondylitis, rheumatoid arthritis, or Arthritis with inflammatory bowel disease. A higher than normal red blood cell count may indicate polycythemia or erythrocytosis, and a higher than normal white blood cell count may indicate leukocytosis. Both polycythemia or leukocytosis may be indicative of inflammatory disease or infection.