C-reactive protein (CRP) is a phase protein synthesized by hepatocytes. Usually in healthy people, the plasma level is very low and its increase is not specific for infection.

Orthopedic surgeon sometimes uses the CRP measurement as a diagnostic tool for infection and for monitoring the effect of the treatment. Uncomplicated cardiac surgery, abdominal surgery, and uncomplicated total hip arthroplasty could induce a temporary rise in CRP (Larsson et al. 1992). Larsson et al. (1992) reported a CRP increase in all the patients examined, after an elective orthopedic surgery, and this is probably due to the tissue damage. They observed different peak levels probably correlated to the amount of tissue injured but also to the type of tissue being damaged. They also reported that the operation time, gender, age, drug history, anesthetic, and blood transfusion did not significantly influence CRP response.

Some authors (White et al. 1998) reported that CRP levels begin to increase 6 h after the trauma, with a peak level in 48–72 h, with return to normal level within 3–6 weeks in the absence of complications.

Dupont et al. (2008) reported that CRP level changes in three phases: it firstly increases up to a peak (reached at POD 2–3) of seven to 14 times the normal range. After POD 3 the level falls rapidly and then decreases more slowly until the normalization at three or four postoperative week. A CRP value of 25 mg/l at POD 21 has a 100 % specificity regardless of the location of the infection, but low sensitivity (58.3 %). Gomez-Navalon et al. (2000) reported a sensitivity of 63.3 % and a specificity of 80.1 % for CRP and judged alpha-1 antitrypsin to be more reliable, with a sensitivity of 87.5 % and a specificity of 85.8 % in detecting infections.

Okafor and Maclellan (1998) also described the trend of CRP. They reported that CRP rises till a mean value of 0.146 g/dl at POD 2 in the normal group versus 0.2 in the infected group. In the infected group, a persistent elevation on day 7 and day 21 was observed. In the same study, the authors have evaluated also the erythrocyte sedimentation rate (ESR); usually the variations were significantly different for day 0 versus POD 2 and day 0 versus POD 7, but not for day 0 versus POD 21. In the infected group, the postoperative values of ESR were significantly different from day 0 value, reflecting the persistent inflammatory state. ESR value depends on multifactorial variable, so the reliability is low and high value has to be interpreted with caution. They concluded that CRP shows less variability between patients and consequently is a better indicator of the acute phase response than ESR, which requires a series of values in order to demonstrate a trend.