Is it beneficial to have C-Reactive Protein (CRP) levels checked?

C-Reactive Protein (CRP) Testing: Clinical Benefits and Applications

CRP testing is beneficial in specific clinical scenarios including monitoring response to antibiotic treatment in bacterial infections, assessing cardiovascular risk in intermediate-risk patients, and evaluating disease activity in inflammatory conditions, but should not be used routinely in all patients due to its limited specificity. 1, 2

Clinical Utility of CRP Testing

Infection and Inflammation Monitoring

• CRP is a valuable marker for monitoring response to antibiotic treatment in known bacterial infections 3
• CRP levels correlate well with the degree of inflammatory response, making them useful for tracking treatment response 1
• Serial measurements are more informative than single values - the direction of change over time provides valuable information on inflammation progression 2
• CRP begins to rise 12-24 hours after an inflammatory insult, reaching maximum values after 48 hours 1

Cardiovascular Risk Assessment

• High-sensitivity CRP (hsCRP) is recommended for patients at intermediate risk (10-20% risk of coronary heart disease per 10 years) 2
• CRP risk categories for cardiovascular disease:
  • Low risk: <1.0 mg/L
  • Average risk: 1.0-3.0 mg/L
  • High risk: >3.0 mg/L 2
• For accurate cardiovascular risk assessment, two measurements (optimally 2 weeks apart) should be obtained after resolution of any acute inflammatory stimulus 2

Other Beneficial Applications

• Early detection of complications in postoperative patients 3
• Monitoring disease activity and response to disease-modifying drugs in rheumatoid arthritis 3
• Differentiating between active disease and infections in patients with systemic lupus and ulcerative colitis (when baseline response patterns are established) 3
• Early warning of intrauterine infections in obstetric patients with premature rupture of membranes 3

Limitations and Caveats

• CRP has limited specificity (40-67%) as a marker of bacterial infection and should not be used in isolation to rule in or rule out a specific diagnosis 2
• The Society of Critical Care Medicine and Infectious Diseases Society of America recommend against routine use of biomarkers in sepsis and septic shock due to uncertain benefit and cost issues 1
• CRP levels ≥10 mg/L should prompt evaluation for sources of infection or inflammation 2
• CRP levels can be influenced by:
  • Non-pathological factors: age, sex, socioeconomic status, race, BMI, exercise, diet, sleep, and medications 2
  • Underlying conditions: rheumatoid arthritis, inflammatory bowel disease, chronic alcoholism 2
  • Lifestyle factors: smoking, obesity, poor sleep 2

Interpretation Guidelines

• A single elevated CRP measurement after injury should not be used to assess cardiovascular risk 2
• CRP levels in acute inflammation/bacterial infection typically range from 40-200 mg/L 2
• Severe acute illness may produce CRP levels >500 mg/L 2
• Clinical context and other laboratory findings are essential when interpreting CRP results 2
• In geriatric patients hospitalized with acute infection, CRP dosage at admission is helpful to detect acute infection, particularly sepsis, and may provide valuable short-term prognostic information 4

When to Order CRP Testing

CRP testing is most beneficial when:

1. Monitoring known bacterial infections during treatment 3
2. Assessing cardiovascular risk in intermediate-risk patients 2
3. Evaluating disease activity in inflammatory conditions like rheumatoid arthritis 3
4. Investigating for infection in patients with fever, chills, hypothermia, leukocytosis, left-shift of neutrophils, or neutropenia 1
5. Monitoring patients after surgery for early detection of complications 3

In the setting of fever with lower likelihood of infection, CRP may be useful to obtain a baseline value to assist in the discontinuation of antimicrobial therapy 1.