There is no simple blood test or non-invasive way to confirm the diagnosis of GCA. The erythrocyte sedimentation rate (or sed rate) is a blood test that measures inflammation by checking to see how the rate at which red blood cells (erythrocytes) sediment (or fall) within an hour. This rate is high in most people with GCA. Because other diseases can cause high sedimentation rates, doctors cannot rely on this finding alone as proof of GCA. In some cases, an ultrasound of the temporal arteries on the side of head can be done. If positive this can be suggestive of active GCA. A negative test, however, does not rule out GCA and biopsy would need to be done. It is common to do a biopsy – or surgical removal – of a small piece of the temporal artery and study it under a microscope for signs of inflammation. This biopsy is an outpatient procedure, done under local anesthesia (numbing of that site while you are awake). It leaves just a small scar that usually cannot be seen at the hairline in front of the ear. In GCA, the biopsy shows inflammation of the artery. If there is doubt about the diagnosis based on the first biopsy, your doctor may do a biopsy of the temporal artery on the other side of your head.
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