From the Guidelines
There is limited benefit to ordering both an ESR and CRP test simultaneously in most clinical scenarios, and CRP alone is generally sufficient for detecting and monitoring inflammatory conditions. The most recent and highest quality study 1 recommends performing both ESR and CRP at baseline in the investigation for diagnosis and prognosis of undifferentiated peripheral inflammatory arthritis, but this is a specific clinical context. In general, CRP is preferred due to its quicker response to inflammation and faster normalization when inflammation resolves. However, there are specific situations where ordering both might be justified, such as in certain rheumatologic conditions or complex cases where the pattern of elevation between the two tests might provide additional information.
- Key points to consider:
- CRP responds more quickly to inflammation, rising within 4-6 hours and peaking at 24-48 hours, while ESR changes more slowly, taking 24-48 hours to increase and remaining elevated for weeks 1.
- CRP normalizes faster when inflammation resolves, making it better for monitoring acute changes 1.
- ESR has established diagnostic criteria in certain rheumatologic conditions, such as giant cell arteritis or polymyalgia rheumatica 1.
- The combination of an abnormal sedimentation rate and CRP may provide the best combination of sensitivity and specificity in certain clinical contexts, such as suspected prosthetic joint infection 1.
- In most routine clinical practice, CRP alone is sufficient and more cost-effective for detecting and monitoring inflammatory conditions, but clinical judgment is required to determine when additional testing, such as ESR, may be necessary 1.
From the Research
Benefits of Ordering ESR with CRP
- There is limited benefit to ordering an ESR if a CRP is already being ordered, as CRP is more sensitive and specific for monitoring acute inflammation 2.
- ESR can be helpful in monitoring chronic inflammatory conditions, whereas CRP is more useful in diagnosis and monitoring responses to therapy in acute inflammatory conditions 3.
- The two tests can provide complementary information, but they can also disagree in up to 33% of patients, and the causes of these disagreements can be complex 4.
Clinical Applications
- ESR and CRP should be used in combination with clinical history and physical exam for diagnosis and monitoring of pathological conditions, as they lack sensitivity or specificity on their own 5.
- Discrepancies between ESR and CRP measurements can occur, particularly in chronic inflammatory diseases, and can be influenced by various physiological factors 5.
- Normal levels of inflammatory markers like CRP and ESR do not rule out the diagnosis of certain conditions, such as giant cell arteritis, and clinical presentation should be taken into account 6.
Test Utilization
- Reducing unnecessary ESR orders and ESR/CRP co-ordering rates can be achieved through quality improvement projects and electronic health record initiatives 2.
- Understanding the physiologic principles behind ESR and CRP, as well as the factors that can affect their measurements, is important for proper utilization and interpretation of these tests 3, 5.