We do CRPs at my hospital on baby's who we think are septic whether they are newborns or ones who have been in the unit for a long time and suddenly get sick. I have heard somewhere that even a paper cut can cause a person's CRP level to rise a little...
The book, "Fetal & Neonatal Secrets, Second Edition" by Polin & Spitzer has some very good information about the CRP in the chapter on Infection & Immunity which I will share below:
Question #35. What is the relevance of C-reactive protein (CRP) in the diagnosis of neonatal sepsis?
Answer: Serum CRP is an acute phase reactant, which becomes elevated in the face of inflammation or infection, with a response time of 6-8 hours. The normal value in the neonate is <1.0 mg/dL. An elevated CRP level 12-24 hours after the onset of possible sepsis has a positive predictive value of only 7-43%, but a negative predictive value of 97-99.5%, thus, CRP is quite useful in ruling out sepsis. A marked elevation of CRP level (>5.0 mg/dL) has a positive value for sepsis of 10%. (References: Benitz WB, Han MY, Madan A, Ramachandra P: Serial serum C-reactive protein levels in the diagnosis of neonatal infection. Pediatrics 102:E41, 1998. and Gerdes JS: Clinicopathologic approach to the diagnosis of neonatal sepsis. Perinatol 18:361-381, 1991.)
Question #36. Can a normal white blood cell (WBC) count, immature-to-total (I:T) neutrophil ratio, neutrophil count, or CRP measurement be used to rule out sepsis on admission?
Answer: Unfortunately not. Neither these nor any other tests can be used to reliably rule out infection in neonates. The usefulness of the tests improves markedly with serial measurements because there have been many cases of sepsis described in which the WBC count or CRP level became abnornal 12-24 hours after the onset of the disease. Furthermore, these tests can be combined in a sepsis screen in which several parameters are used to improve the diagnostic accuracy.
Question #39. What studies are useful in creating a sepsis screen strategy?
Answer: Although diagnostic tests are frequently ordered to identify infants with probable sepsis, their main benefit is to exclude disease in infants with a low probability of infection. A combination of diagnostic tests improves the predictive values over the use of a single test. In this strategy, serial sepsis screens that have negative results substantially reduce the likelihood that the infant has sepsis. One suggested screen is given in Table 12-7. The screen result is considered positive if 2 or more points are present. It is important to recognize that no sepsis screen is perfect, and one should err on the side of caution with neonatal sepsis.
Table 12-7. Parameters for Sepsis Screen Strategy
Test Point Value
Absolute neutrophil count <1750/mm3 1 point
Total WBC <7500 ro >40,000/mm3 1 point
I:T neutrophil ratio > or =to 0.2 1 point
I:T neutrophil ratio > or =to 0.4 2 points
CRP+ (> or =to 1.0 mg/dL) 1 point
CRP+ (> or =to 5.0 mg/dL) 2 points
I love this book and highly recommend it to NICU nurses for many reasons.