CRP - Revision history

Danbot: Add Category:Labs

2026-03-22T06:44:00Z

← Older revision		Revision as of 06:44, 22 March 2026
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Danbot: Formatting: moved intro to Background bullets, removed excessive bold from bullet lead-ins

2026-03-19T15:53:15Z

Formatting: moved intro to Background bullets, removed excessive bold from bullet lead-ins

← Older revision		Revision as of 15:53, 19 March 2026
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	~~'''~~C-reactive protein (CRP)~~'''~~ is an acute-phase reactant produced by the liver in response to [[Interleukin-6\|IL-6]] stimulation during inflammation, infection, or tissue injury. It is one of the most commonly ordered inflammatory markers in the ED but is ~~'''~~nonspecific~~'''~~ — it rises in virtually any inflammatory state.<ref name="Pepys2003">Pepys MB, Hirschfield GM. C-reactive protein: a critical update. ''J Clin Invest''. 2003;111(12):1805-1812.</ref>		==Background==
			*C-reactive protein (CRP) is an acute-phase reactant produced by the liver in response to [[Interleukin-6\|IL-6]] stimulation during inflammation, infection, or tissue injury.
			*It is one of the most commonly ordered inflammatory markers in the ED but is nonspecific — it rises in virtually any inflammatory state.<ref name="Pepys2003">Pepys MB, Hirschfield GM.
			*C-reactive protein: a critical update. ''J Clin Invest''. 2003;111(12):1805-1812.</ref>


	~~==Background==~~
	*CRP rises within 6–8 hours of an inflammatory stimulus, peaks at ~48 hours, and has a plasma half-life of ~19 hours<ref name="Pepys2003"/>		*CRP rises within 6–8 hours of an inflammatory stimulus, peaks at ~48 hours, and has a plasma half-life of ~19 hours<ref name="Pepys2003"/>
	*Levels fall rapidly with resolution of the stimulus, making CRP useful for trending disease activity		*Levels fall rapidly with resolution of the stimulus, making CRP useful for trending disease activity
	*CRP is produced exclusively by hepatocytes; severe liver failure may blunt the CRP response<ref name="Pepys2003"/>		*CRP is produced exclusively by hepatocytes; severe liver failure may blunt the CRP response<ref name="Pepys2003"/>
	*Two assays exist:		*Two assays exist:
	**~~'''~~Standard CRP:~~'''~~ Measures levels typically >10 mg/L; used for detecting infection and inflammation		**Standard CRP: Measures levels typically >10 mg/L; used for detecting infection and inflammation
	**~~'''~~High-sensitivity CRP (hs-CRP):~~'''~~ Measures levels <10 mg/L; used for cardiovascular risk stratification (not typically useful in acute ED settings)		**High-sensitivity CRP (hs-CRP): Measures levels <10 mg/L; used for cardiovascular risk stratification (not typically useful in acute ED settings)

	==Normal Values==		==Normal Values==
	*~~'''~~Normal:~~'''~~ <10 mg/L (some labs use <5 mg/L or <3 mg/L as cutoff)		*Normal: <10 mg/L (some labs use <5 mg/L or <3 mg/L as cutoff)
	*~~'''~~Mild elevation:~~'''~~ 10–50 mg/L — viral infections, mild inflammation, most autoimmune flares		*Mild elevation: 10–50 mg/L — viral infections, mild inflammation, most autoimmune flares
	*~~'''~~Moderate elevation:~~'''~~ 50–100 mg/L — significant bacterial infection or active inflammatory disease		*Moderate elevation: 50–100 mg/L — significant bacterial infection or active inflammatory disease
	*~~'''~~Marked elevation:~~'''~~ >100 mg/L — strongly suggests serious bacterial infection, sepsis, major trauma, or severe pancreatitis<ref name="Clyne1999">Clyne B, Olshaker JS. The C-reactive protein. ''J Emerg Med''. 1999;17(6):1019-1025.</ref>		*Marked elevation: >100 mg/L — strongly suggests serious bacterial infection, sepsis, major trauma, or severe pancreatitis<ref name="Clyne1999">Clyne B, Olshaker JS. The C-reactive protein. ''J Emerg Med''. 1999;17(6):1019-1025.</ref>
	*~~'''~~Extreme elevation:~~'''~~ >200 mg/L — often seen in [[Sepsis\|sepsis]], [[Necrotizing fasciitis\|necrotizing soft tissue infection]], or extensive burns		*Extreme elevation: >200 mg/L — often seen in [[Sepsis\|sepsis]], [[Necrotizing fasciitis\|necrotizing soft tissue infection]], or extensive burns

	==ED Applications==		==ED Applications==
	===Where CRP adds value===		===Where CRP adds value===
	*~~'''~~Trending:~~'''~~ Serial CRP measurements are more useful than a single value — a rising CRP suggests clinical deterioration; a falling CRP supports treatment response		*Trending: Serial CRP measurements are more useful than a single value — a rising CRP suggests clinical deterioration; a falling CRP supports treatment response
	*~~'''~~Pediatric fever without source:~~'''~~ CRP >80 mg/L increases the likelihood of serious bacterial infection in febrile children<ref name="Sanders2008">Sanders S, et al. Systematic review of the diagnostic accuracy of C-reactive protein to detect bacterial infection in nonhospitalized infants and children with fever. ''J Pediatr''. 2008;153(4):570-574.</ref>		*Pediatric fever without source: CRP >80 mg/L increases the likelihood of serious bacterial infection in febrile children<ref name="Sanders2008">Sanders S, et al. Systematic review of the diagnostic accuracy of C-reactive protein to detect bacterial infection in nonhospitalized infants and children with fever. ''J Pediatr''. 2008;153(4):570-574.</ref>
	*~~'''~~[[Appendicitis]]:~~'''~~ A normal CRP (especially combined with normal WBC and no left shift) has a high negative predictive value for appendicitis, particularly if symptoms >24 hours<ref name="Andersson2004">Andersson RE. Meta-analysis of the clinical and laboratory diagnosis of appendicitis. ''Br J Surg''. 2004;91(1):28-37.</ref>		*[[Appendicitis]]: A normal CRP (especially combined with normal WBC and no left shift) has a high negative predictive value for appendicitis, particularly if symptoms >24 hours<ref name="Andersson2004">Andersson RE. Meta-analysis of the clinical and laboratory diagnosis of appendicitis. ''Br J Surg''. 2004;91(1):28-37.</ref>
	*~~'''~~[[Septic arthritis]] vs. transient synovitis:~~'''~~ CRP >20 mg/L is one of the Kocher criteria for distinguishing septic arthritis in the pediatric hip<ref name="Kocher1999">Kocher MS, et al. Differentiating between septic arthritis and transient synovitis of the hip in children: an evidence-based clinical prediction algorithm. ''J Bone Joint Surg Am''. 1999;81(12):1662-1670.</ref>		*[[Septic arthritis]] vs. transient synovitis: CRP >20 mg/L is one of the Kocher criteria for distinguishing septic arthritis in the pediatric hip<ref name="Kocher1999">Kocher MS, et al. Differentiating between septic arthritis and transient synovitis of the hip in children: an evidence-based clinical prediction algorithm. ''J Bone Joint Surg Am''. 1999;81(12):1662-1670.</ref>
	*~~'''~~Undifferentiated infections:~~'''~~ A CRP <20–40 mg/L makes serious bacterial infection less likely in low-risk patients, though it does not rule it out		*Undifferentiated infections: A CRP <20–40 mg/L makes serious bacterial infection less likely in low-risk patients, though it does not rule it out
	*~~'''~~[[Osteomyelitis]]:~~'''~~ CRP elevated in >95% of cases; useful for monitoring treatment response		*[[Osteomyelitis]]: CRP elevated in >95% of cases; useful for monitoring treatment response
	*~~'''~~Neonatal sepsis:~~'''~~ Serial CRP (at presentation and 24–48 hours later) used alongside blood cultures to guide antibiotic duration in neonatal sepsis evaluations		*Neonatal sepsis: Serial CRP (at presentation and 24–48 hours later) used alongside blood cultures to guide antibiotic duration in neonatal sepsis evaluations

	===Where CRP does NOT help===		===Where CRP does NOT help===
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	==CRP vs. Other Inflammatory Markers==		==CRP vs. Other Inflammatory Markers==
	*~~'''~~CRP vs. ESR:~~'''~~ CRP rises and falls faster than ESR; CRP is preferred for acute ED decision-making. ESR is affected by anemia, polycythemia, and paraproteinemias		*CRP vs. ESR: CRP rises and falls faster than ESR; CRP is preferred for acute ED decision-making. ESR is affected by anemia, polycythemia, and paraproteinemias
	*~~'''~~CRP vs. procalcitonin:~~'''~~ Procalcitonin is more specific for bacterial infection and is preferred for guiding antibiotic decisions in [[pneumonia]] and [[sepsis]]. CRP is more sensitive but less specific		*CRP vs. procalcitonin: Procalcitonin is more specific for bacterial infection and is preferred for guiding antibiotic decisions in [[pneumonia]] and [[sepsis]]. CRP is more sensitive but less specific

	==See Also==		==See Also==

Ostermayer: Created page with "'''C-reactive protein (CRP)''' is an acute-phase reactant produced by the liver in response to IL-6 stimulation during inflammation, infection, or tissue injury. It is one of the most commonly ordered inflammatory markers in the ED but is '''nonspecific''' — it rises in virtually any inflammatory state.Pepys MB, Hirschfield GM. C-reactive protein: a critical update. ''J Clin Invest''. 2003;111(12):1805-1812. ==Background==..."

2026-03-10T23:32:20Z

Created page with "'''C-reactive protein (CRP)''' is an acute-phase reactant produced by the liver in response to IL-6 stimulation during inflammation, infection, or tissue injury. It is one of the most commonly ordered inflammatory markers in the ED but is '''nonspecific''' — it rises in virtually any inflammatory state.<ref name="Pepys2003">Pepys MB, Hirschfield GM. C-reactive protein: a critical update. ''J Clin Invest''. 2003;111(12):1805-1812.</ref> ==Background==..."

New page

'''C-reactive protein (CRP)''' is an acute-phase reactant produced by the liver in response to [[Interleukin-6|IL-6]] stimulation during inflammation, infection, or tissue injury. It is one of the most commonly ordered inflammatory markers in the ED but is '''nonspecific''' — it rises in virtually any inflammatory state.<ref name="Pepys2003">Pepys MB, Hirschfield GM. C-reactive protein: a critical update. ''J Clin Invest''. 2003;111(12):1805-1812.</ref>

==Background==
*CRP rises within 6–8 hours of an inflammatory stimulus, peaks at ~48 hours, and has a plasma half-life of ~19 hours<ref name="Pepys2003"/>
*Levels fall rapidly with resolution of the stimulus, making CRP useful for trending disease activity
*CRP is produced exclusively by hepatocytes; severe liver failure may blunt the CRP response<ref name="Pepys2003"/>
*Two assays exist:
**'''Standard CRP:''' Measures levels typically >10 mg/L; used for detecting infection and inflammation
**'''High-sensitivity CRP (hs-CRP):''' Measures levels <10 mg/L; used for cardiovascular risk stratification (not typically useful in acute ED settings)

==Normal Values==
*'''Normal:''' <10 mg/L (some labs use <5 mg/L or <3 mg/L as cutoff)
*'''Mild elevation:''' 10–50 mg/L — viral infections, mild inflammation, most autoimmune flares
*'''Moderate elevation:''' 50–100 mg/L — significant bacterial infection or active inflammatory disease
*'''Marked elevation:''' >100 mg/L — strongly suggests serious bacterial infection, sepsis, major trauma, or severe pancreatitis<ref name="Clyne1999">Clyne B, Olshaker JS. The C-reactive protein. ''J Emerg Med''. 1999;17(6):1019-1025.</ref>
*'''Extreme elevation:''' >200 mg/L — often seen in [[Sepsis|sepsis]], [[Necrotizing fasciitis|necrotizing soft tissue infection]], or extensive burns

==ED Applications==
===Where CRP adds value===
*'''Trending:''' Serial CRP measurements are more useful than a single value — a rising CRP suggests clinical deterioration; a falling CRP supports treatment response
*'''Pediatric fever without source:''' CRP >80 mg/L increases the likelihood of serious bacterial infection in febrile children<ref name="Sanders2008">Sanders S, et al. Systematic review of the diagnostic accuracy of C-reactive protein to detect bacterial infection in nonhospitalized infants and children with fever. ''J Pediatr''. 2008;153(4):570-574.</ref>
*'''[[Appendicitis]]:''' A normal CRP (especially combined with normal WBC and no left shift) has a high negative predictive value for appendicitis, particularly if symptoms >24 hours<ref name="Andersson2004">Andersson RE. Meta-analysis of the clinical and laboratory diagnosis of appendicitis. ''Br J Surg''. 2004;91(1):28-37.</ref>
*'''[[Septic arthritis]] vs. transient synovitis:''' CRP >20 mg/L is one of the Kocher criteria for distinguishing septic arthritis in the pediatric hip<ref name="Kocher1999">Kocher MS, et al. Differentiating between septic arthritis and transient synovitis of the hip in children: an evidence-based clinical prediction algorithm. ''J Bone Joint Surg Am''. 1999;81(12):1662-1670.</ref>
*'''Undifferentiated infections:''' A CRP <20–40 mg/L makes serious bacterial infection less likely in low-risk patients, though it does not rule it out
*'''[[Osteomyelitis]]:''' CRP elevated in >95% of cases; useful for monitoring treatment response
*'''Neonatal sepsis:''' Serial CRP (at presentation and 24–48 hours later) used alongside blood cultures to guide antibiotic duration in neonatal sepsis evaluations

===Where CRP does NOT help===
*CRP '''cannot distinguish''' between bacterial and viral infection at moderate elevations (10–80 mg/L) — significant overlap exists
*CRP does not localize infection (will be elevated in pneumonia, UTI, cellulitis, abscess equally)
*A '''single normal CRP early in illness''' (<12 hours from symptom onset) does not exclude serious infection — CRP may not have risen yet
*Extremely elevated CRP (>200 mg/L) is not specific to infection — also seen in rheumatologic flares ([[gout]], [[rheumatoid arthritis]], crystal arthropathies), malignancy, and major surgery/trauma

==Causes of Elevated CRP==
*Bacterial infection (including [[sepsis]], [[pneumonia]], [[meningitis]], intra-abdominal infections)
*Viral infections (usually milder elevation)
*Autoimmune/rheumatologic disease ([[Rheumatoid arthritis]], [[lupus]], [[vasculitis]], [[Inflammatory bowel disease|IBD]], [[gout]])
*Tissue injury (surgery, trauma, burns, MI)
*Malignancy (especially lymphoma, renal cell carcinoma)
*[[Pancreatitis]]
*[[Deep venous thrombosis]] / [[pulmonary embolism]]

==Causes of Low/Normal CRP Despite Active Disease==
*Very early infection (<6–8 hours from onset)
*Severe hepatic failure (impaired CRP synthesis)
*Immunosuppressive therapy (some biologics, e.g., tocilizumab/IL-6 inhibitors, directly suppress CRP production regardless of active infection — this is a critical pitfall)<ref name="Pepys2003"/>
*SLE flares (CRP often modestly elevated or normal in lupus flares, unlike most other autoimmune conditions — a markedly elevated CRP in a lupus patient suggests superimposed infection rather than flare)

==CRP vs. Other Inflammatory Markers==
*'''CRP vs. ESR:''' CRP rises and falls faster than ESR; CRP is preferred for acute ED decision-making. ESR is affected by anemia, polycythemia, and paraproteinemias
*'''CRP vs. procalcitonin:''' Procalcitonin is more specific for bacterial infection and is preferred for guiding antibiotic decisions in [[pneumonia]] and [[sepsis]]. CRP is more sensitive but less specific

==See Also==
*[[Sepsis]]
*[[Appendicitis]]
*[[Septic arthritis]]
*[[Osteomyelitis]]
*[[HIV post-exposure prophylaxis]]

==References==
{{reflist|2}}

[[Category:ID]]