Review Question - QID 3719

A normalized C-reactive protein (CRP) value (< 3 mg/L) would be the most likely value seen in a patient with a resolution of a post-op wound infection. Erythrocyte sedimentation rate (ESR) has been shown to decrease at a much slower place and its normalization is much less specific for infection resolution.

CRP has been found to correlate with clinical response in patients treated with antibiotics for wound infection following spinal surgery. ESR has been found to remain elevated despite the presence of resolution of clinical symptoms and normalized CRP in these patients. It must be recognized that CRP can be elevated for reasons other than infection, including a slight increase with aging, rise during late pregnancy, and abnormal levels with liver failure. Similarly, ESR can be increased with pregnancy, some renal diseases, cancer, and anemia. Additionally, it can be decreased in sickle cell, leukemia, congestive heart failure, and hyperviscosity. Normal ESR values are between 0-15 mm/hr for men under age 50 and between 0 and 20 mm/hr and for women under age 50.

Khan et al. studied 21 patients with postoperative wound infections after spinal surgery. Of 21 patients they found resolution of all postoperative wound infections at the 20-week mark, and found that all patient had normalized CRPs (mean 0.8 mg/dL). However, they found ESR remained elevated (mean 29 mm/hr) despite normalized CRPs and complete resolution of signs and symptoms of infection.

Fang et al. reviewed 48 patients with post-operative spinal surgery wound infections and compared to a random control group of 95 uninfected spinal surgery patients. They noted that Age >60 years, smoking, diabetes, previous surgical infection, increased body mass index, and alcohol abuse were all statistically significant preoperative risk factors for developing a post-op wound infection.. The most likely procedure to be complicated by an infection was a combined anterior/posterior spinal fusion performed in a staged manner under separate anesthesia. Infections were primarily monomicrobial and the most common organism cultured from the wounds was Staphylococcus aureus.

Illustration A shows the CRP trends in the study by Khan et al. with postoperative wound infections after spinal surgery treated with IV antibiotics. ER refers to early responder while LR refers to late responder. At the 4-week time point, 16 patients have shown clinical improvement with no fevers, wound drainage, erythema, or need for wound packing. The other 5 patients, referred to as late responders, have shown one or more clinical signs of infection in addition to having an elevated CRP. At 20 weeks, both early and late responders both have shown normalized CRP levels and no clinical evidence of infection. Illustration B shows the ESR trends in the those which demonstrated incomplete normalization of ESR values despite resolution of infection.


Incorrect Answers:
Answer 1, 2, 3, 5: CRP levels > 3 mg/L are elevated and indicate incomplete response to infection