Is C-reactive protein (CRP) elevated in giant cell arteritis?

Elevated CRP in Giant Cell Arteritis

Yes, C-reactive protein (CRP) is typically elevated in giant cell arteritis, with a sensitivity of approximately 79.2% and a negative likelihood ratio of 0.38, making it a valuable diagnostic marker for the condition. 1

Diagnostic Value of CRP in GCA

CRP as a Key Laboratory Marker

• CRP elevation is a significant laboratory finding in GCA diagnosis:
  • Sensitivity: 79.2% (63.5-89.3%) 1
  • Negative likelihood ratio: 0.38 (0.25-0.59) 1
  • A normal CRP level significantly decreases the likelihood of GCA diagnosis

Comparison with ESR

• Both CRP and ESR are important inflammatory markers in GCA:
  • CRP is slightly more sensitive than ESR (79.2% vs 82.6%) 1
  • A normal CRP has a stronger negative likelihood ratio (0.38) than a normal ESR (0.51) 1
  • ESR >40 mm/h has the strongest negative likelihood ratio (0.18) 1

Pretreatment CRP Values

• Pretreatment elevated CRP shows even higher sensitivity:
  • Sensitivity: 90.1% (76.3%-96.3%) 1
  • Negative likelihood ratio: 0.38 (0.17-0.81) 1
  • This emphasizes the importance of obtaining CRP levels before starting corticosteroid treatment

Clinical Implications

Diagnostic Algorithm

1. Obtain both CRP and ESR in all patients with suspected GCA
2. Normal CRP and ESR together significantly reduce the likelihood of GCA (odds ratio 0.49) 2
3. If both inflammatory markers are normal, consider alternative diagnoses, though GCA is still possible in ~4% of cases 2
4. If either CRP or ESR is elevated, proceed with further diagnostic evaluation

Important Caveats

• A small proportion (4%) of GCA patients may have normal inflammatory markers at diagnosis 2
• These patients more commonly present with polymyalgia rheumatica symptoms and less frequently with constitutional symptoms, anemia, or thrombocytosis 2
• In cases where traditional markers are normal but clinical suspicion remains high, high-sensitivity CRP may be useful 3

Monitoring Disease Activity

• CRP normalizes more rapidly than ESR during treatment:
  • 67% of patients have normal CRP after two weeks of treatment 4
  • 56% of patients have normal ESR after two weeks of treatment 4
• During disease relapses:
  • CRP may be normal in up to 56% of cases 5
  • ESR may be normal in 48% of cases 5

Complementary Diagnostic Features

Clinical Features with Strong Diagnostic Value

• Limb claudication: positive likelihood ratio 6.01 6
• Jaw claudication: positive likelihood ratio 4.90 6
• Temporal artery thickening: positive likelihood ratio 4.70 6
• Temporal artery loss of pulse: positive likelihood ratio 3.25 6
• Platelet count >400 × 10³/μL: positive likelihood ratio 3.75 1

Emerging Biomarkers

• Serum S100A8/S100A9 and S100A12 proteins are elevated during active GCA and may complement ESR and CRP as disease activity markers 7
• A model combining S100 proteins with ESR and CRP may provide better indication of disease activity than traditional markers alone 7

In clinical practice, the absence of elevated CRP significantly reduces the likelihood of GCA, but does not completely rule it out. When evaluating patients with suspected GCA, obtaining both CRP and ESR provides the most comprehensive laboratory assessment.