White blood cell and platelet counts can be used to differentiate between infection and the normal response after splenectomy for trauma: prospective validation.

Background: 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.
Methods: 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.
Results: 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.
Conclusion: 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.