Investigations
1st investigations to order
CRP
Test
Take blood for measuring CRP before starting a high-dose glucocorticoid (see Management recommendations).[36][39]
Note that inflammatory markers decrease once glucocorticoid therapy is started.[35][36]
Result
typically elevated
ESR
Test
Take blood for measuring ESR before starting a high-dose glucocorticoid (see Management recommendations).[36][39]
Note that inflammatory markers decrease once glucocorticoid therapy is started.[35][36]
Result
typically elevated
FBC
Test
Take blood for FBC before starting a high-dose glucocorticoid (see Management recommendations).[36][39]
Result
patients may have a normochromic, normocytic anaemia with a normal WBC count and elevated platelet count; mild leukocytosis may occur
vascular ultrasonography
Test
If available, use rapid-access vascular ultrasonography of the temporal and axillary artery first line to diagnose suspected GCA.[35][36][38] In a subset of patients with cranial GCA, there will be simultaneous involvement of upper extremity vessels - therefore, axillary and subclavian arteries are assessed alongside temporal arteries in some centres, as part of baseline assessment.
Ultrasonography reduces the number of patients who need a temporal artery biopsy and has the advantage of being non-invasive and more cost effective, and the rapid bedside availability may help to reduce sight loss.[36][44][45][46][47]
Ultrasonography is best performed in validated centres.[36][48]
Diagnostic ultrasonography for GCA should be performed within 7 days of starting glucocorticoids.[37] Rapid access is important as the ultrasound ‘halo’ diminishes in size once glucocorticoid therapy has been started.[44] Ultrasonography appearances may normalise 2-4 weeks after commencing glucocorticoids.[37][49]
In patients in whom there is a high clinical suspicion of GCA and a positive imaging result, the diagnosis of GCA may be made without an additional test (biopsy or further imaging).[38] In patients with a low clinical probability and a negative imaging result, the diagnosis of GCA can be considered unlikely. In all other situations (including the case of an inconclusive imaging result), further investigations to reach a diagnosis are required.[38]
Result
may show halo sign, stenosis, or occlusion; a non-compressible halo sign is the finding that most indicates GCA[38]
temporal artery biopsy
Test
Consider a temporal artery biopsy if:
Expertise for ultrasonography is not available
The patient’s pre-test probability is high (typical features of GCA with raised inflammatory markers) but the ultrasonography is normal.[36]
A biopsy should be performed by a surgeon experienced in this procedure.[36] The biopsy is performed on the side with abnormal clinical findings (if present). Specimens should be no shorter than 1 cm (post-fixation) due to the possibility of skip lesions.[35][36] In one study, the diagnostic yield was improved by having a specimen of at least 5 mm length, which was examined at multiple levels.[51]
Do not delay treatment while waiting for the biopsy to be performed (see Management recommendations).[36] The biopsy should be harvested within 4 weeks of starting glucocorticoids.[37]
However, even after several weeks of glucocorticoid therapy, temporal artery biopsy may still yield a diagnosis of arteritis.[52][53] Indeed, the majority of temporal artery biopsies (9 out of 12) performed in a small cohort of patients with treated GCA had persistent histopathological evidence of vasculitis even after 6 months of glucocorticoid therapy.[54] Ongoing vasculitis was apparent in 4 out of 9 biopsies after 12 months of treatment.
Temporal artery biopsy is less helpful in patients with extracranial GCA and may be negative in up to 50% of these patients.[55] This may be due to skip lesions, involvement of arteries besides the superficial temporal artery, duration of treatment with prednisolone prior to procedure, incorrect operative technique, or inadequate examination of the biopsy specimen. However, even people thought to have extracranial disease may have a positive temporal artery biopsy in some cases and thorough investigation is always warranted.
Result
histopathology typically shows granulomatous inflammation; in about 50% of cases, multinucleated giant cells are present; inflammatory infiltrate may be focal and segmental
liver function tests
Test
Consider further tests to establish major organ system function, such as liver function tests.
Mild abnormalities are common and should resolve with treatment. Persisting or severe abnormalities should prompt a screen for an underlying cause, including malignancy and hepatitis, symptoms of which may mimic GCA in some patients.
Result
transaminases and alkaline phosphatase are sometimes mildly elevated
renal function tests
Test
Consider further tests to establish major organ system function, such as renal function tests.
Mild abnormalities are common and should resolve with treatment. Persisting or severe abnormalities should prompt a screen for an underlying cause, including malignancy and hepatitis, symptoms of which may mimic GCA in some patients.
Result
may be mildly abnormal but consider other causes
Investigations to consider
fluorodeoxyglucose (FDG)-PET scan of head to mid-thigh
Test
A combined PET-CT scan using 18-fluorodeoxyglucose as a radioactive label is of value in individuals who have a negative ultrasonography but in whom there is clinical suspicion of extracranial disease.[38] The diagnostic yield falls rapidly after the onset of glucocorticoid therapy and it should be done within 7 days of the request to avoid false negative results.[37]
It is of value in defining the extent of disease and in the demonstration of malignancies which form an important differential diagnosis of GCA.
It is not used routinely in the assessment of cranial GCA.
Result
may demonstrate FDG uptake in the large vessels (aorta and major branches)
high-resolution MRI of cranial arteries
Test
Consider high-resolution MRI of the cranial arteries, if available, as a further diagnostic test or if neither vascular ultrasound or temporal artery biopsy are available.[36][38]
It would not be a first choice due to the lack of formal validation, availability, and the expertise required, and also the possibility of adverse effects to the contrast agents used.[36]
Result
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