Is C-reactive protein (CRP) elevated in patients with gout and infection?

C-Reactive Protein Elevation in Gout and Infection

C-reactive protein (CRP) is significantly elevated in both gout and infection, with infection typically causing higher CRP levels (40-200 mg/L) compared to the mild to moderate elevation (10-40 mg/L) seen in gout. 1

CRP Elevation Patterns

In Infection:

• CRP levels typically range from 40-200 mg/L in bacterial infections 1
• Severe acute infections can cause CRP levels >500 mg/L 1
• CRP increases dramatically (up to 1,000-fold) at sites of infection 2
• CRP rises rapidly in response to infection and decreases just as rapidly with resolution 3

In Gout:

• Gout typically causes mild to moderate CRP elevation (10-40 mg/L) 1
• During acute gout flares, CRP levels increase significantly 4
• CRP is positively correlated with other inflammatory markers like ESR in gout 4
• A case report showed high CRP levels during gout flares, with one patient having CRP of 23.16 mg/dL (231.6 mg/L) during a severe flare 5

Clinical Interpretation Guidelines

Risk Categorization:

• Low risk: <1.0 mg/L
• Average risk: 1.0-3.0 mg/L
• High risk: >3.0 mg/L
• Mild inflammation: 10-40 mg/L
• Acute inflammation/bacterial infection: 40-200 mg/L
• Severe acute illness: >500 mg/L 1

Important Considerations:

• CRP is an acute-phase reactant produced primarily by the liver 2
• CRP has limited specificity (40-67%) as a marker of bacterial infection 1
• Serial measurements are more informative than single values 1
• If CRP level is ≥10 mg/L, the test should be repeated and the patient examined for sources of infection or inflammation 6

Differential Diagnosis of Elevated CRP

High CRP (>40 mg/L):

• Bacterial infections
• Severe inflammatory conditions
• Combined conditions (e.g., gout with concurrent infection) 1, 5

Moderate CRP (10-40 mg/L):

• Gout and other crystal arthropathies
• Autoimmune diseases
• Mild infections
• Tissue injury 1

Clinical Pitfalls and Caveats

1. Coexisting conditions: Consider the possibility of concurrent gout and infection, as demonstrated in a case where a patient had both gout flares and Chlamydia-induced reactive arthritis 5

2. Non-pathological factors affecting CRP levels include:

   • Age, sex, race
   • Body mass index
   • Exercise, diet, sleep
   • Medication use 1

3. Limited specificity: CRP elevation alone cannot differentiate between gout and infection; clinical context and other laboratory findings are essential 1

4. Measurement considerations:

   • For stable patients, two measurements (optimally 2 weeks apart) should be averaged 6
   • CRP results should be expressed in mg/L to one decimal point 6
   • A highly sensitive method for measuring CRP is recommended 6

5. Underlying conditions: Inflammatory conditions like rheumatoid arthritis, inflammatory bowel disease, and chronic alcoholism may result in mildly to moderately increased CRP levels 6

By understanding these patterns and considerations, clinicians can better interpret CRP levels in the context of suspected gout or infection, recognizing that while both conditions elevate CRP, the degree of elevation and clinical context help distinguish between them.