Which laboratory tests are most useful in the initial assessment of suspected Giant Cell Arteritis?

The most useful laboratory tests in the initial assessment of a patient with suspected Giant Cell Arteritis (GCA) are:

• Full blood count (FBC) to detect normochromic normocytic anaemia and elevated platelet count, which are common in GCA.
• C-reactive protein (CRP), which is typically elevated in GCA cases.
• Erythrocyte sedimentation rate (ESR), often elevated above 50 mm/hour, although it can be normal in some cases.

These tests should ideally be performed before or immediately after starting high-dose glucocorticoids, but treatment should not be delayed if GCA is strongly suspected.

Additional baseline tests may be considered to exclude alternative diagnoses or assess risk of glucocorticoid adverse effects, including urea and electrolytes, HbA1c, calcium, liver function tests, and others depending on clinical context.

Definitive diagnosis requires specialist assessment with imaging (e.g., temporal artery ultrasound) or biopsy.

Urgent referral and treatment initiation are critical due to the risk of serious complications such as vision loss.

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