Giant cell arteritis can be difficult to diagnose because its early symptoms resemble those of many common conditions. For this reason, your doctor will try to rule out other possible causes of your problem.
To help diagnose giant cell arteritis, you may have some or all of the following tests:
- Physical exam. In addition to asking about your symptoms and medical history, your doctor is likely to perform a thorough physical exam, paying particular attention to your temporal arteries. Often, one or both of these arteries are tender with a reduced pulse and a hard, cord-like feel and appearance.
Blood tests. If your doctor suspects 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. Red cells that drop rapidly may indicate inflammation in your body.
You may also have a test that measures C-reactive protein (CRP), a substance your liver produces when inflammation is present. The same tests may be used to follow your progress during treatment.
Biopsy. The best way to confirm a diagnosis of giant cell arteritis is by taking a small sample (biopsy) of the temporal artery. Because the inflammation may not occur in all parts of the artery, more than one sample may be needed. 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.
If you have giant cell arteritis, the artery will often show inflammation that includes abnormally large cells, called giant cells, which give the disease its name. Unfortunately, a biopsy isn't foolproof. It's possible to have giant cell arteritis and still have a negative biopsy result. If the results aren't clear, your doctor may advise another temporal artery biopsy on the other side of your head.
Although a temporal artery biopsy is the standard test for diagnosing giant cell arteritis, imaging tests may also be used for diagnosing giant cell arteritis and for monitoring treatment. Possible tests include:
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- Magnetic resonance angiography (MRA). This test combines the use of magnetic resonance imaging (MRI) with the use of a contrast material that produces detailed images of your blood vessels. Let your doctor know ahead of time if you're uncomfortable being confined in a small space because the test is conducted in a tube-shaped machine.
- Doppler ultrasound. This test uses sound waves to produce images of blood flowing through your blood vessels.
- Positron emission tomography (PET). Using an intravenous tracer solution that contains a tiny amount of radioactive material, a PET scan can produce detailed images of your blood vessels and highlight areas of inflammation.
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