What are ESR and CRP?
ESR and CRP are markers of inflammation that rise in response to both acute and chronic inflammation.
ESR is an indirect measure of inflammation that measures the rate at which red blood cells settle in a test tube. It is affected by multiple factors, including the concentration of fibrinogen in the blood, and can be elevated in a variety of conditions besides inflammation.
CRP is a more direct measure of inflammation that is produced by the liver in response to acute infection or inflammation. It is also affected by other factors, such as age, sex, race, and body mass index.
Although ESR and CRP are both biomarkers of inflammation, they have different patterns of response. CRP begins to rise within hours of the start of an infection or inflammatory condition, while ESR levels rise more slowly. CRP also returns to normal levels more quickly than ESR.
As a result, CRP is a more sensitive marker of the acute inflammatory response, especially within the first few days of a process.
Elevated ESR and CRP levels indicate inflammation but not its location. These markers are nonspecific and should be interpreted in conjunction with a thorough clinical evaluation. While CRP is more sensitive for acute inflammation, ESR is better suited for monitoring chronic inflammation. Combining both tests enhances diagnostic accuracy and provides valuable insights into the nature of the inflammatory process.
Normal values for ESR include:
· Children: < 10 mm/hr
· Males and females < 50 yo: < 15 and 20 mm/hr, respectively
· Males and females >50 yo: < 20 and 30 mm/hr, respectively
Normal values for the standard CRP test include:
· Normal: < 1 mg/dL
· Moderate elevation: 1-10 mg/dL
· Significant elevation: > 10 mg/dL
Clinical Utility in the ED:
There are 3 main instances in the ED where ESR and CRP may be of value to the ED clinician:
Back Pain - When ESR or CRP are elevated in the setting of back pain, sensitivity can range from 94% to 100%, and often there are significant elevations in ESR and CRP, even in the absence of leukocytosis
· Spinal epidural abscess
· Vertebral osteomyelitis
· Malignancy/spinal tumors
Bottom line: Elevated ESR and CRP can help determine the need for an MRI, but normal levels should not rule out serious diagnoses such as spinal epidural abscess or osteomyelitis in high-risk patients. In patients with intermediate or low pretest probability for spinal epidural abscess, a low ESR may be used to exclude the condition.
Skin and soft tissue infections - In the emergency department (ED) setting, it is crucial to identify patients who require inpatient admission and consider necrotizing soft tissue infections (NSTIs) as a potential diagnosis.
· Cellulitis
· Necrotizing soft tissue infections
Bottom line: While ESR and CRP can provide insights into the severity and treatment response of skin and soft tissue infections (SSTIs), they should not alter emergency department (ED) management or surgical consultation decisions for patients with NSTI. These biomarkers, though useful, lack specificity for SSTIs and may appear normal in some individuals with the condition.
Joint and bone pain
· Septic arthritis
· Osteomyelitis
Bottom line: Elevated ESR and CRP levels may heighten the suspicion of osteomyelitis, but they cannot definitively confirm or rule out the condition. Arthrocentesis remains essential for diagnosing septic joint infections.
References
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Nehring SM, Goyal A, Patel BC. C Reactive Protein. [Updated 2022 Jul 18]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK441843/
Bray C, Bell LN, Liang H, Haykal R, Kaiksow F, Mazza JJ, Yale SH. Erythrocyte Sedimentation Rate and C-reactive Protein Measurements and Their Relevance in Clinical Medicine. WMJ. 2016 Dec;115(6):317-21. PMID: 29094869.
Siemionow K, Steinmetz M, Bell G, Ilaslan H, McLain RF. Identifying serious causes of back pain: cancer, infection, fracture. Cleveland Clinic journal of medicine. 2008;75(8):557-566. doi:10.3949/ccjm.75.8.557
Stevens DL, Baddour LM. Necrotizing soft tissue infections. Post TW, ed. UpToDate. Waltham, MA: UpToDate Inc. http://www.uptodate.com. (Accessed on April 22, 2023.)
Hariharan P, Kabrhel C. Sensitivity of erythrocyte sedimentation rate and C-reactive protein for the exclusion of septic arthritis in emergency department patients. J Emerg Med. 2011 Apr;40(4):428-31. doi: 10.1016/j.jemermed.2010.05.029. Epub 2010 Jul 22. PMID: 20655163.