Utility of CRP in Emergency Departments

C-reactive protein (CRP) is an acute phase protein synthesized in the liver. It is commonly used in Emergency Departments, especially in febrile and possibly infectious patients. It is also used as a measure of tissue inflammation, a biomarker of disease activity and a prognostic tool of many acute and chronic diseases. CRP functions as a bacterial opsonin, promoting phagocytosis, accelerating chemotaxis, and activating platelets. Normal levels increase with aging. Other possible reasons for higher levels could be:

• Pregnancy
• Coronary Artery Disease
• Viral Infections (10–40 mg/L)
• Bacterial infection (>40mg/dL)
• Malignancy, Obstructive Sleep Apnea, Connective Tissue Disorders

Serial CRP measurements may be helpful to monitor a patient’s response to medical intervention. Although CRP rises with tissue injury or ischemia, in septic patients with fulminant hepatic failure, it is more to be a marker of severe liver dysfunction rather than be used as a marker of infection.

Utility of CRP

1. ACS and Aortic Dissection - For ACS and Dissection, the higher CRP levels, the worse prognosis. It is not used to diagnose ACS/Dissection. Increased CRP levels were independently associated with mortality. 

2. Meningitis - For meningitis, CRP plays a role of distinguishing bacteria from non-bacteria etiology infection.

3. CRP in Acute Abdomen pain
CRP cannot play a suitable role in the diagnosis of cholecystitis but can be a factor indicating the severity of cholecystitis and response to therapy. A normal CRP along with a normal WBC count and a normal neutrophil count is unlikely to be a case of appendicitis. Although early in the course of appendicitis, the white blood cell (WBC) count has shown the best diagnostic sensitivity among laboratory tests, there are 21% of appendicitis is normal levels of WBC count before appendectomy. 

An elevated serum CRP concentration is not accurate in localizing the site of a urinary tract infection in girls who do not have clinical signs of acute pyelonephritis. 

There is no substitute for serial and prudent clinical examinations during an observation period for abdominal pain, especially the initial epigastric pain or peri-umbilical pain.

4. Pnemonia

For pneumonia, CRP plays the roles of prognosis prediction and therapy reflector rather than making diagnosis. CRP is an independent biomarker of severity in community-acquired pneumonia. 

5. Sepsis
Sepsis is a clinical diagnosis and CRP should never used be rule out infection. Procalcitonin has emerged as the most studied and promising sepsis biomarker. For diagnostic and prognostic purposes in critical care, PCT is superior to CRP and other traditional markers of sepsis.


Take Home

In the ED, CRP should not be used to make a diagnosis but to assist evaluation and support your clinical suspicion. In clinically unwell patients, a normal CRP level should never delay antibiotic coverage in ED.  Like other biomarkers, it does not stand alone. In admitted patinets or those on thepary for chronic inflammatory states, CRP can be used for treatment monitoring and severity. 

References

1. Su YJ. The value of C-reactive protein in emergency medicine. Journal of Acute Disease. 2014 Jan 1;3(1):1-5.
2. Rossi E. C-reactive protein and progressive atherosclerosis.Lancet 2002; 360(9344): 1436-1437.
3. Schillinger M, Domanovits H, Bayegan K, Hölzenbein T, Grabenwöger M, Thoenissen J, et al. C-reactive protein and mortality in patients with acute aortic disease. Intensive Care Med2002; 28(6): 740-745.

Posted by:

              

     Lakshay Chanana

     

     ST4 Trainee

     Royal Infirmary of Edinburgh

     Department of Emergency Medicine

     Edinburgh

     Scotland

     @EMDidactic