From the Guidelines
Elevated C-Reactive Protein (CRP) and elevated Erythrocyte Sedimentation Rate (ESR) are both markers of inflammation, but CRP is more sensitive and specific for acute inflammation and infection, whereas ESR is more indicative of chronic inflammation and can be affected by various comorbidities. The key differences between CRP and ESR lie in their response times and specificities. CRP levels tend to rise more quickly with infection and fall more quickly with the resolution of infection, making it a more reliable marker for monitoring treatment response 1. In contrast, ESR values can be affected by various comorbidities, such as anemia and azotaemia, and may not be elevated in acute infections due to its relatively slow response. Some of the key points to consider when interpreting CRP and ESR results include:
- CRP levels are significantly higher in infected than noninfected diabetic foot ulcers (DFUs) and increase with the severity of infection 1
- ESR values are higher in patients with an infected DFU compared with a noninfected DFU, but can be influenced by comorbidities and may not be elevated in acute infections 1
- A highly elevated ESR (≥70 mm/h) has a sensitivity, specificity, and AUC for the diagnosis of diabetic foot osteomyelitis (DFO) of 81%, 80%, and 0.84, respectively 1
- CRP has shown higher diagnostic accuracy for grade 2 (infected) DFU compared to WBC and ESR 1 In clinical practice, CRP is preferred for monitoring acute inflammation and infection, while ESR may be more useful for chronic conditions. However, it is essential to interpret these tests in the context of the patient's clinical presentation, as neither test can diagnose a specific disease on its own.
From the Research
Differences between Elevated C-Reactive Protein (CRP) and Elevated Erythrocyte Sedimentation Rate (ESR)
- Elevated CRP is more sensitive and specific for monitoring acute inflammation, whereas elevated ESR is helpful in monitoring chronic inflammatory conditions 2, 3
- CRP has a shorter half-life compared to fibrinogen (which ESR is an indirect measure of), making CRP more useful in diagnosis and monitoring responses to therapy in acute inflammatory conditions 2
- ESR is more useful in monitoring chronic inflammatory conditions due to the longer half-life of fibrinogen 2
Clinical Significance of Discordance between ESR and CRP Measurements
- Discordance between ESR and CRP measurements can occur due to various physiological factors, including noninfectious conditions and resolution of inflammation 4
- Underlying infection, renal insufficiency, and low serum albumin can contribute to abnormally high ESR/low CRP readings or vice versa 5
- In patients with nonspecific clinical findings and sustained elevations in serum ESR/CRP levels, the most common etiology of nonspecific elevations in ESR/CRP levels was new onset rheumatic disease, followed by infections and malignancies 6
Factors Affecting ESR and CRP Measurements
- Many factors can result in falsely high or low ESR and CRP levels, and it is essential to take note of these factors when interpreting test results 2, 4
- Low serum albumin was associated with both kinds of discordance (elevated ESR/low CRP and elevated CRP/low ESR) 5
- CRP levels were significantly higher in infections compared to new onset rheumatic disease or malignancies 6