What tests and treatment should be ordered for a giant cell arteritis (GCA) workup?

Giant Cell Arteritis Workup

The diagnostic workup for giant cell arteritis (GCA) should include erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), complete blood count with platelets, and temporal artery biopsy, with immediate initiation of high-dose glucocorticoid therapy if clinical suspicion is high. 1

Clinical Assessment for GCA

When evaluating a patient for possible GCA, focus on these key clinical features with their associated likelihood ratios:

High-Value Clinical Findings

• Limb claudication (positive LR 6.01) 2
• Jaw claudication (positive LR 4.90) 2, 1
• Temporal artery abnormalities:
  • Thickening (positive LR 4.70) 2
  • Loss of pulse (positive LR 3.25) 2
  • Tenderness (positive LR 3.14) 2
• Age ≥50 years (absence of age >70 years has negative LR 0.48) 2, 1
• New-onset localized headache 1

Laboratory Testing

Order these tests immediately for suspected GCA:

1. Erythrocyte sedimentation rate (ESR):

   • ESR >100 mm/h has positive LR 3.11 2
   • Absence of ESR >40 mm/h has negative LR 0.18 (strong evidence against GCA) 2, 1
   • Sensitivity 84-89% 3, 4

2. C-reactive protein (CRP):

   • Absence of CRP ≥2.5 mg/dL has negative LR 0.38 2, 1
   • Sensitivity 86-100% (higher than ESR) 3, 4

3. Complete blood count with platelets:

   • Platelet count >400 × 10³/μL has positive LR 3.75 2, 1
   • High specificity (88%) but lower sensitivity (38%) 5

Important caveat: While inflammatory markers are typically elevated in GCA, approximately 4-15% of cases may present with normal ESR, and about 0.8% may have both normal ESR and normal CRP 6, 7, 3. Therefore, normal inflammatory markers do not rule out GCA if clinical suspicion remains high.

Diagnostic Confirmation

Temporal Artery Biopsy

• Gold standard for diagnosis 1, 6
• Obtain a long-segment specimen (>1 cm) to reduce false negatives from "skip lesions" 1
• Should be performed within 2 weeks of starting glucocorticoids 1
• Initially, perform unilateral biopsy on the symptomatic side 1

Vascular Imaging (if biopsy is negative but suspicion remains high)

• Vascular ultrasound: Non-invasive, high sensitivity and specificity 1, 6
• MRI/MRA of cranial arteries 1
• CT angiography 1
• FDG-PET/CT in select cases 1

Treatment Initiation

• Start high-dose glucocorticoids immediately if clinical suspicion is high, even before diagnostic confirmation, due to risk of permanent vision loss 1
• Prednisone 40-60 mg/day for initial treatment 1
• IV methylprednisolone 500-1000 mg/day for patients with visual symptoms 1
• Consider tocilizumab to reduce glucocorticoid requirements and prevent relapses 1

Diagnostic Algorithm

1. Assess clinical features for likelihood of GCA
2. Order laboratory tests: ESR, CRP, and CBC with platelets
3. Initiate glucocorticoids immediately if clinical suspicion is high
4. Arrange temporal artery biopsy within 2 weeks of starting treatment
5. If biopsy is negative but suspicion remains high, proceed with vascular imaging
6. Refer urgently to specialists for patients with visual symptoms or other high-risk features 1

Clinical pearl: The combination of CRP and platelet count can allow for faster initial decision-making without waiting for ESR results, as sequential analysis has shown ESR may not provide additional diagnostic value when the other markers are available 5.