Blood tests. If your doctor thinks you might have giant cell arteritis, you're likely to have a blood test that checks your erythrocyte sedimentation rate — commonly referred to as the sed rate.This test measures how quickly red blood cells fall to the bottom of a tube of blood.he best way to confirm a diagnosis of giant cell arteritis is by taking a small sample (biopsy) of the temporal artery. The procedure is performed on an outpatient basis during local anesthesia, usually with little discomfort or scarring. The sample is examined under a microscope in a laboratory.