Tests
1st tests to order
CRP
Test
Elevated in the majority of patients. CRP is not affected by anemia. Occasionally the CRP is elevated with a normal erythrocyte sedimentation rate. CRP level ≥10 mg/L is one factor that supports the diagnosis of giant cell arteritis.[1]
Result
elevated
erythrocyte sedimentation rate (ESR)
Test
ESR ≥50 mm/hour by the Westergren method is one of the supportive features for diagnosis cited in the American College of Rheumatology classification criteria.[1] A minority of patients may have a normal ESR.
An ESR of >100 mm/hour is helpful in predicting a positive temporal artery biopsy (likelihood ratio of 1.9).[61]
If patients have been on glucocorticoid therapy prior to testing of acute-phase reactants, the result may be lower than expected.
Result
ESR ≥50 mm/hour by the Westergren method
CBC
Test
Should be checked in all patients with suspected giant cell arteritis. Significant elevation of the WBC count should prompt an evaluation for possible hematologic malignancy.
Result
typically, patients have a normochromic, normocytic anemia with a normal WBC count and elevated platelet count; mild leukocytosis may occur
LFTs
Test
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 giant cell arteritis in some patients.
Result
transaminases and alkaline phosphatase are often mildly elevated
temporal artery biopsy
Test
Temporal artery biopsy is considered the definitive test for the diagnosis of giant cell arteritis (GCA).[1][35] However, imaging is being increasingly used for diagnosis and ultrasound is the preferred early imaging test.[1][41]
For patients with suspected GCA, initially, a unilateral biopsy is recommended.[35] The biopsy is performed on the side with abnormal clinical findings (if present). However, bilateral temporal artery biopsies may be appropriate if the symptoms are not clearly localized to one temporal artery.[35]
If the biopsy on one side is normal, a second biopsy on the contralateral side may be considered.[35] The pathologic process is patchy; therefore, an adequate sample of temporal artery (>1 cm) is required to improve the diagnostic yield.[35]
Temporal artery biopsy is less helpful in patients with large-vessel GCA and may be negative in up to 50% of these patients.[40]
Result
histopathology typically shows granulomatous inflammation; in about 50% of cases, multinucleated giant cells are present; inflammatory infiltrate may be focal and segmental
temporal artery ultrasound
Test
Ultrasound has the advantage of being noninvasive, cost-effective, and widely available. A temporal artery halo sign (wall thickening) on ultrasound is a supporting diagnostic feature of giant cell arteritis (GCA).[1] Ultrasound may also show stenosis or occlusion. It has been suggested that the diagnosis of GCA can be made on the basis of the clinical syndrome and ultrasonography findings without resorting to temporal artery biopsy.[42] However, it is operator-dependent and is best performed in experienced centers, where it may be a useful and complementary tool for diagnosing GCA.[35] Results are influenced by treatment (i.e., signs of inflammation quickly disappear with glucocorticoid treatment).[35]
Systematic reviews of temporal artery ultrasonography have reported a pooled sensitivity of 87% and a specificity of 96% compared with the clinical diagnosis, and a sensitivity of 75% and specificity of 83% compared with temporal artery biopsy.[42][43] In a meta-analysis of 20 studies, the sensitivity and specificity of a hypoechoic halo (halo sign) compared with positive temporal artery biopsy were 68% and 81%, respectively.[44]
European guidelines recommend ultrasound as the preferred early imaging test in patients with suspected GCA.[41]
Result
may show halo sign, stenosis or occlusion; bilateral axillary involvement
Tests to consider
noninvasive vascular imaging
Test
Ultrasound, CT angiography, or magnetic resonance angiography of the aortic arch and great vessels is performed in patients with suspected large-vessel involvement.[1] Imaging the large vessels of the neck/chest/abdomen/pelvis may provide additional evidence of extracranial disease when the diagnosis remains suspected following negative temporal artery biopsy results.[35]
Radiographic findings of large-vessel involvement are frequently seen. However, large-vessel involvement is clinically apparent in about 10% to 15% of patients with giant cell arteritis.[7]
Result
may show homogeneous, concentric, thickening stenosis or occlusion of the subclavian, axillary, or proximal brachial arteries; radiographic appearance is usually one of smoothly tapered stenoses; lower-extremity vasculature is rarely involved; thickening or edema of the aortic wall can indicate aortitis
Emerging tests
18F-fluorodeoxyglucose (FDG)-PET scan of head to mid-thigh
Test
May be useful as an emerging diagnostic tool and in the assessment of active disease, where it may demonstrate FDG uptake in the large vessels (aorta and major branches).[1][45][46][47][48]
In patients with elevated markers of inflammation and uncertain diagnosis, FDG-PET may be helpful in detecting an occult malignancy or infection in patients who present with constitutional symptoms similar to vasculitis.[45] However, in routine clinical practice, FDG-PET is not currently able to assess inflammation in the superficial temporal arteries. FDG-PET may have some utility for the assessment of persistent or recurrent giant cell arteritis (GCA) in the appropriate clinical context.[49] The main concern with FDG-PET/CT is that its sensitivity is affected by immunosuppression.[45][50][51][52] Within 3 days of high-dose glucocorticoid treatment, FDG PET/CT can diagnose large-vessel GCA with high sensitivity. After 10 days of treatment, FDG PET/CT sensitivity decreases significantly.[53]
Result
may demonstrate FDG uptake in the large vessels (aorta and major branches)
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