White Blood Cell and Platelet Counts Can Be Used to Differentiate between Infection and the Normal Response after Splenectomy for Trauma: Prospective Validation

Abstract

Transient elevations of the serum white blood cell count (WBC) and platelet count (PC) are normal physiologic responses after splenectomy. The clinician is often challenged to identify an infection in a postsplenectomy patient with an elevated WBC. A previous retrospective study found that a WBC greater than 15 x 10/microL and a PC/WBC ratio < 20 on postoperative day 5, in addition to an Injury Severity Score > 16, were highly associated with infection and should not be considered as part of the physiologic response to splenectomy. The current study intends to prospectively validate the WBC and PC/WBC ratio on postoperative day 5 as markers of infection after splenectomy for trauma. Consecutive trauma patients admitted to an urban, Level I trauma center who underwent splenectomy from June 2002 to December 2004 were collected prospectively. In addition to admission demographics, variables collected included daily WBC, PC, and PC/WBC ratio during the first 10 postoperative days. Outcome was the presence of infection. Patients with infection (infected group) were compared with those without infection (noninfected group). Injury Severity Score > 16, postoperative day 5 WBC > 15 x 10/microL, and PC/WBC ratio < 20 were investigated as risk factors for postsplenectomy infection. There were 96 trauma patients who underwent splenectomy during the study period, and 44 (46%) developed a postoperative infection. Infectious complications included pneumonia (n = 30 [31%]), followed by septicemia (n = 20 [21%]), urinary tract infection (n = 12 [13), abdominal abscess (n = 9 [9%]), and wound infection (n = 4 [4%]). Postoperative day 5 was the first day that infected patients had a higher WBC (16 +/- 6 x 10/microL vs. 14 +/- 4 x 10/microL, p = 0.03) and a lower PC/WBC ratio (15 +/- 9 vs. 24 +/- 12, p = 0.002) than noninfected patients. The presence of two or more risk factors for infection was associated with a 79% rate of infection, and no patient developed an infection if all three risk factors were absent. On postoperative day 5 after splenectomy for trauma, a WBC greater than 15 x 10/microL and a PC/WBC ratio less than 20 are reliable markers of infection.