Editing C-reactive protein (section)

===Diagnostic use===
CRP is used mainly as an inflammation marker. Apart from [[liver failure]], there are few known factors that interfere with CRP production.<ref name=Pepys/> [[Interferon type I#IFN-α|Interferon alpha]] inhibits CRP production from liver cells which may explain the relatively low levels of CRP found during viral infections compared to bacterial infections <ref>{{cite journal | vauthors = Enocsson H, Sjöwall C, Skogh T, Eloranta ML, Rönnblom L, Wetterö J | title = Interferon-alpha mediates suppression of C-reactive protein: explanation for muted C-reactive protein response in lupus flares? | journal = Arthritis and Rheumatism | volume = 60 | issue = 12 | pages = 3755–3760 | date = December 2009 | pmid = 19950271 | doi = 10.1002/art.25042 | doi-access = free }}</ref><ref name="pmid33584722">{{cite journal | vauthors = Enocsson H, Gullstrand B, Eloranta ML, Wetterö J, Leonard D, Rönnblom L, Bengtsson AA, Sjöwall C | title = C-Reactive Protein Levels in Systemic Lupus Erythematosus Are Modulated by the Interferon Gene Signature and CRP Gene Polymorphism rs1205 | journal = Frontiers in Immunology | volume = 11 | issue =  | pages = 622326 | date = 2020 | pmid = 33584722 | pmc = 7876312 | doi = 10.3389/fimmu.2020.622326 | doi-access = free }}</ref>

Measuring and charting CRP values can prove useful in determining disease progress or the effectiveness of treatments. [[ELISA]] and [[radial immunodiffusion]] methods are available for research use, while [[immunoturbidimetry]] is used clinically for CRP and [[nephelometry (medicine)|nephelometry]] is typically used for hsCRP.<ref>{{cite journal | vauthors = Grützmeier S, von Schenck H | title = Four immunochemical methods for measuring C-reactive protein in plasma compared | journal = Clinical Chemistry | volume = 35 | issue = 3 | pages = 461–463 | date = March 1989 | pmid = 2493344 | doi = 10.1093/clinchem/35.3.461 | doi-access = free }}</ref><ref name="pmid12551878" /> Cutoffs for cardiovascular risk assessment have included:
* low: hs-CRP level under 1.0&nbsp;mg/L
* average: between 1.0 and 3.0&nbsp;mg/L
* high: above 3.0&nbsp;mg/L

Normal levels increase with [[aging]].<ref>Thomas, Lothar, ''Labor und Diagnose''. TH-Books, Frankfurt, 2008, p. 1010</ref> Higher levels are found in late [[Pregnancy|pregnant]] women, mild [[inflammation]] and [[viral infection]]s (10–40&nbsp;mg/L), active inflammation, bacterial infection (40–200&nbsp;mg/L), severe [[bacterial infections]] and [[burn]]s (>200&nbsp;mg/L).<ref name="pmid22787338">{{cite journal | vauthors = Chew KS | title = What's new in Emergencies Trauma and Shock? C-reactive protein as a potential clinical biomarker for influenza infection: More questions than answers | journal = Journal of Emergencies, Trauma, and Shock | volume = 5 | issue = 2 | pages = 115–117 | date = April 2012 | pmid = 22787338 | pmc = 3391832 | doi = 10.4103/0974-2700.96477 | doi-access = free }}</ref>

CRP cut-off levels indicating bacterial from non-bacterial illness can vary due to [[co-morbidities]] such as [[malaria]], [[HIV]] and [[malnutrition]] and the stage of disease presentation.<ref>{{cite journal | vauthors = Dittrich S, Tadesse BT, Moussy F, Chua A, Zorzet A, Tängdén T, Dolinger DL, Page AL, Crump JA, D'Acremont V, Bassat Q, Lubell Y, Newton PN, Heinrich N, Rodwell TJ, González IJ | title = Target Product Profile for a Diagnostic Assay to Differentiate between Bacterial and Non-Bacterial Infections and Reduce Antimicrobial Overuse in Resource-Limited Settings: An Expert Consensus | journal = PLOS ONE | volume = 11 | issue = 8 | pages = e0161721 | date = 2016-08-25 | pmid = 27559728 | pmc = 4999186 | doi = 10.1371/journal.pone.0161721 | veditors = Yansouni C | doi-access = free | bibcode = 2016PLoSO..1161721D }}</ref> In patients presenting to the emergency department with suspected sepsis, a CRP/albumin ratio of less than 32 has a negative predictive value of 89% for ruling out sepsis.<ref>{{cite journal | vauthors = Sisto UG, Di Bella S, Porta E, Franzoi G, Cominotto F, Guzzardi E, Artusi N, Giudice CA, Dal Bo E, Collot N, Sirianni F, Russo S, Sanson G | title = Predicting sepsis at emergency department triage: Implementing clinical and laboratory markers within the first nursing assessment to enhance diagnostic accuracy | journal = Journal of Nursing Scholarship | date = June 2024 | volume = 56 | issue = 6 | pages = 757–766 | pmid = 38886920 | doi = 10.1111/jnu.13002 }}</ref>

CRP is a more sensitive and accurate reflection of the acute phase response than the ESR<ref name="pmid23689052"/> ([[erythrocyte sedimentation rate]]). ESR may be normal while CRP is elevated. CRP returns to normal more quickly than ESR in response to therapy.{{citation needed|date=July 2022}}