How elevated is C-Reactive Protein (CRP) in patients with giant cell arteritis?

Elevated CRP in Giant Cell Arteritis

C-reactive protein (CRP) is significantly elevated in giant cell arteritis (GCA), with approximately 79.2% of patients showing elevated levels. 1 This makes CRP an important diagnostic marker for this condition.

Degree of CRP Elevation in GCA

• CRP elevation in GCA is typically substantial, with a positive likelihood ratio of 4.50 for diagnosing GCA 1
• The negative likelihood ratio of 0.38 means that a normal CRP level significantly reduces the probability of GCA 1, 2
• CRP normalization occurs relatively quickly with treatment, with 67% of patients showing normal values after just two weeks of corticosteroid therapy 3

Comparison with Other Inflammatory Markers

CRP elevation should be interpreted alongside other inflammatory markers:

• Erythrocyte Sedimentation Rate (ESR):

  • 82.6% of GCA patients have elevated ESR 1
  • ESR >100 mm/h has a positive likelihood ratio of 3.79 1
  • ESR >40 mm/h has a stronger negative likelihood ratio (0.18) than CRP (0.38) 1, 2

• Platelet Count:

  • 45.8% of GCA patients have thrombocytosis (>400 × 10³/μL) 1
  • Positive likelihood ratio of 3.75 for GCA diagnosis 1, 2
  • Less predictive than CRP or ESR but still significant 4

• Anemia:

  • Present in 87.4% of GCA patients 1
  • Positive likelihood ratio of 3.16 1

Clinical Implications

1. Diagnostic Value:

   • CRP elevation combined with typical clinical features significantly increases the probability of GCA
   • Normal CRP significantly reduces the likelihood of GCA, though rare cases with normal CRP do exist (approximately 0.8% of cases) 5

2. Treatment Monitoring:

   • CRP decreases rapidly with corticosteroid treatment, making it useful for monitoring treatment response 3
   • CRP normalizes faster than haptoglobin but at a similar rate to fibrinogen 3

3. Atypical Presentations:

   • In cases with normal traditional inflammatory markers, high-sensitivity CRP may still be elevated 6
   • Some patients may have occult GCA with normal standard inflammatory markers 6

Practical Approach

When evaluating a patient with suspected GCA:

1. Check both CRP and ESR, as the combination improves diagnostic accuracy

2. Consider the presence of clinical features alongside CRP elevation:

   • New-onset headache, especially temporal
   • Jaw claudication (positive likelihood ratio 4.90) 2
   • Visual symptoms
   • Polymyalgic symptoms
   • Constitutional symptoms (weight loss, fatigue, fever)

3. Remember that while CRP elevation is highly sensitive (79.2%), a small percentage of GCA cases may present with normal CRP levels 5

4. If clinical suspicion remains high despite normal inflammatory markers, consider high-sensitivity CRP testing and vascular imaging 6

The combination of clinical features and laboratory findings, particularly elevated CRP and ESR, remains the cornerstone for prompt diagnosis of GCA, which is crucial to prevent irreversible complications such as vision loss.