WBC and C-Reactive Protein (CRP) Definition The C - reactive protein (CRP) is a plasma protein of hepatic origin, having a major role in the inflammatory reaction. The name derives from its interaction with the C-polysaccharide (CPS) for which it requires calcium ions.1 The CRP measurement is proved to be relevant for the diagnosis and for the prognosis of diseases wherever inflammatory processes are involved. Structure CRP belongs to the pentraxin family of calcium-dependent ligand-binding plasma proteins, which also includes too the serum amyloid P component (SAP). This structure is a rare configuration due to the conserved pentameric arrangement of the protomers. Indeed, CRP contents 5 protomers of each 206 amino-acid and its molecular weight is about 23kDa.2 Synthesis process An acute-phase inflammatory response occurs when the human body triggers a systemic response following tissue injury by infectious, noninfectious, chemical, physical, or immunologic toxin causes. CRP is a protein increasing during the acute-phase response and is regulated by cytokines, like interleukin-1 (IL-1), interleukin-6 (IL-6), and tumor necrosis factor (TNF-α), which are known to increase by at least 25% during the inflammatory response. These cytokines stimulate hepatocytes to increase the synthesis and release of positive acute-phase proteins, including CRP. IL-6 is the major cytokine stimulus for CRP production.3 Page | 1 WBC and C-Reactive Protein (CRP) Measurement CRP is a well-established biomarker in clinical laboratories for the diagnosis of inflammation or infection. It is an acute-phase protein whose concentration increases rapidly in response to various stimuli including inflammation, bacterial infection, trauma, surgery. Its measurement in routine analysis has been largely developed. Many CRP immunoassays are commercially available and, performed on plasma or serum samples, are mainly based on particle-enhanced turbidimetry or nephelometry using latex microbead. This technology has been modified and further adapted to whole blood samples by HORIBA Medical allowing overcome possible interferences with cellular element. Indeed, the instruments of the HORIBA Medical CRP series provide doctors with efficient equipment which allows performing in less than 4 minutes a Complete Blood Count (CBC) or 5-differential (5-DIFF) together with an immunoassay measuring CRP up to 200mg/L. This is a unique solution that has made HORIBA Medical the leader in this field already for more than 15 years. The determination of all these parameters on a unique blood sample avoids separation of plasma or serum from blood cells and therefore constitutes an important procedure simplification and reduction of analysis time. This is made possible by using of an infrared light source for which cell debris and hemoglobin diffusion/absorption is negligible with respect to the specific signal due to particle aggregates formation in response to the presence of CRP. Concentration In normal plasma of healthy people CRP median values are around 1mg/L. However, values of 5-10 mg/L CRP can still be considered normal in healthy people who have no signs of infection or 4 inflammation . In any case, all CRP values must be interpreted in the clinical context. The normal CRP concentration in the elderly may be more elevated than1mg/L. In apparently healthy people, CRP measures of about 2-3mg/L have been linked to risk of cardiovascular diseases and this range is denominated as high sensitive CRP (hs-CRP). The serum concentration of CRP increases rapidly within hours upon immunological insult, microbial infection or tissue damage.5 In individuals with acute and severe illness, cytokines, IL-6, stimulate hepatic production of CRP and plasma levels may increase up to 300mg/L or more. Page | 2 WBC and C-Reactive Protein (CRP) Role in Biology CRP is highly expressed during the acute phase of inflammatory reactions. The protein behaves like an antibody by its several functions associated with host defense: it promotes agglutination, bacterial capsular swelling and phagocytosis, and activates the classical complement pathway through its calcium-dependent binding to phosphocholine.6 Quantitative measure of CRP level in serum has widespread clinical use as sensitive marker of inflammation. The circulating value of CRP reflects ongoing inflammation and/or tissue damage much more accurately than do other laboratory parameters of the acute-phase response, such as plasma viscosity and the erythrocyte sedimentation rate (ESR). CRP is a reliable indicator of acute inflammatory processes than ESR and leukocyte count. Blood CRP levels rise more rapidly than ESR, and after the disease has subsided CRP values rapidly fall and reach the reference interval often days before ESR has returned to normal. Neonatal sepsis occurs in about 1 to 8 cases/1000 live births.7 Early detection is hampered by vague, nonspecific or nonexistent clinical manifestations. Neonates, especially those born preterm, often fail to induce elevations in temperature and white blood cell (WBC) counts that are the hallmarks of infection in older children. Therefore CRP increase can be used to reveal hidden infections wherever WBC and fever are not reliable as in newborns. In addition CRP doesn’t cross the placenta (or in exceedingly low quantities) differently from procalcitonin (PCT), another protein involved in the inflammatory immune response. Therefore, at birth, CRP elevation in the neonate represents endogenous synthesis from the newborn and not derived from the mother. So CRP elevation is a reliable parameter differently from other biomarkers that, for their molecular structure, can cross the placenta barrier and give misleading results.8 Page | 3 WBC and C-Reactive Protein (CRP) Inflammation In case of inflammation, which is the general mechanism induced by our body in response to an aggression, CRP values are raised and its analysis can be advantageous. CRP is an excellent marker of the acute inflammatory response and is used extensively for diagnosis and prognosis of rheumatologic and other diseases. CRP is routinely used to measure disease activity in rheumatoid arthritis. Similarly measuring CRP levels is helpful in monitoring disease course of various forms of vasculitis.9 CRP elevation in inflammatory bowel disease patients is associated with clinical disease activity, endoscopic inflammation, severely active histologic inflammation (in Crohn Diseases patients), and several other biomarkers of inflammation, but not with radiographic activity.10 Moreover in ulcerative colitis, a combination of the stool markers with the CRP and a disease-specific activity index can increase the diagnostic accuracy with reference to the endoscopic inflammation. According to these observations, CRP appears in the serum following inflammation induced by different etiologies and in response to a variety of stimuli related to disease biology. Bacterial/viral infection CRP concentration in plasma/serum shows a significant increase in various conditions like bacterial infections. This increase arrives very early following the stimulus and it is a sensitive indicator of most forms of microbial infection. CRP responses occur with more intensity in bacterial than in viral infection. The CRP level is widely used to detect bacterial infections in children with fever and in neonates with suspected sepsis. Key functions of CRP in the innate immune system include the ability to recognize and bind to phosphocholine exposed in damaged cell walls and found in many bacteria, fungi, and parasites. It acts like an opsonin, marking bacteria, damaged cell walls, and nuclear debris for phagocytosis. It binds to C1, the first component of the classical pathway of the complement system that triggers phagocytic activity; and bind to polymorphonuclear leukocytes (PMNs) and monocytes, which stimulate the production of inflammatory cytokines. Page | 4 WBC and C-Reactive Protein (CRP) Urinary infections are a common type of pediatric disease, and their treatment and prognosis are closely correlated with infection location. Common clinical manifestations and laboratory tests are insufficient to differentiate between acute pyelonephritis (APN) and lower urinary tract infection (UTI). CRP can be used for upper and lower urinary tract infection differentiation. The serum CRP mean level of the APN (70mg/L) was significantly higher than the UTI (20mg/L). 11 CRP can be also used for example in the diagnosis of neonatal meningitis. The level is increased in most forms of acute and chronic inflammatory states including sepsis syndromes. CRP is, perhaps, the most widely used biomarker of infection in critically ill patients. Human Immunodeficiency Virus (HIV) infection has been frequently associated with chronic inflammation as well as depression. CRP is positively associated with depression in people with HIV infection (serum level of CRP>3mg/L).12 CRP concentration has useful prognostic value in patient with HIV associated to Tuberculosis (TB). High CRP values (≥50mg/L) were strongly associated with poor prognostic clinical features, higher mycobacterial load, and increased frequency of disseminated TB and higher risk of death.13 In particular in low respiratory tract infections (accounting for about 6.9% global mortality), differentiating viral from bacterial causes is important in order to decide about the pertinence of antibiotic therapy. The serum CRP concentration is almost 2-fold higher in acute bacterial infected patients than in acute viral infected patients