Which initial investigations are recommended for confirming a diagnosis of giant cell arteritis?

For initial investigations to support a diagnosis of giant cell arteritis (GCA), blood tests are recommended in primary care before or immediately after commencing high-dose glucocorticoids ¹. These include a full blood count, C-reactive protein (CRP), and erythrocyte sedimentation rate (ESR) ¹. Typically, the CRP level is elevated, and the ESR is often greater than 50 mm/hour, although it can be normal at presentation or during a flare ¹. Other common blood test abnormalities include normochromic normocytic anaemia and an elevated platelet count ¹.

Depending on the clinical situation, other initial investigations may be indicated to exclude alternative diagnoses or identify risks for glucocorticoid-related adverse effects ¹. These can include baseline urea and electrolytes, HbA1c, calcium, and liver function tests ¹. If the ESR is disproportionately elevated compared to CRP, serum protein electrophoresis and urine Bence–Jones protein/serum-free light chains may be considered ¹. Screening tests for serious infection risk (e.g., urine dipstick, chest X-ray, latent tuberculosis tests) and osteoporosis risk (e.g., TSH, vitamin D, bone density test, DEXA) may also be relevant ¹.

It is crucial not to delay referral to a specialist or the initiation of glucocorticoid treatment while waiting for laboratory results if GCA is strongly suspected ¹. Definitive diagnosis relies on further assessment and investigation in secondary care, typically involving imaging such as temporal and axillary artery ultrasound, or a temporal artery biopsy ¹. All people with suspected GCA should have at least one of these confirmatory diagnostic tests ¹.