The efficacy of blood culture in postoperative patients

Blood cultures are often obtained in postoperative patients to rule out bloodstream infections. Our study objectives were to determine the efficacy of blood cultures in postoperative patients with suspected sepsis and to determine variables predisposing patients to positive cultures. This was a retrospective study including patients with blood cultures drawn from January to March 2009 at our institution. We recorded demographics, presence of fever (temperature 101.5 degrees F or higher), elevated white blood cell count (12,000/microL or greater), central line, diabetes, intensive care unit admission, postoperative day of blood draw, National Research Council surgical wound classification, and pre- or postoperative antibiotics. Blood cultures were drawn from 150 patients undergoing surgery within 30 days prior. Sixteen had positive cultures and nine were true-positives (6.3%). There was no statistical difference (P > 0.05) between patients with positive and negative cultures except that those with negative cultures were more likely to have received preoperative antibiotics (P = 0.0186). Blood cultures are invasive, expensive tests with low yield. We recommend that blood cultures be drawn in patients not receiving preoperative antibiotics who have undergone surgery more than 4 days before culture.