Determining the normative reference values for acute-phase inflammatory markers 3 days after lumbar fusion surgery by using the e-norms method.

Background Context: Surgical site infection (SSI) is a devastating complication that greatly increases the duration of hospital stays, health care costs and morbidity/mortality rates. Therefore, early diagnosis and treatment are also very important. Postoperative inflammatory markers are usually used to screen for SSI. However, the feasibility of these markers for the early detection of SSI remains unclear since it is not ideal to use a marker for which normative reference values do not exist.

Purpose: To validate the use of the e-norms method for establishing a normative reference range for acute-phase inflammatory marker levels 3 days after lumbar fusion surgery for early screening of postoperative SSI.

Study Design: A retrospective analysis.

Patient Sample: This study included 907 patients who underwent lumbar fusion surgery (SSI vs. non-SSI: 28 vs. 879).

Outcome Measures: White blood cell (WBC) count, neutrophils count, lymphocyte count, C-reactive protein (CRP) and Erythrocyte sedimentation rate (ESR).

Methods: We applied the e-norms method to calculate reference values for postoperative 3-day CRP, ESR, and differential WBC count in all 907 patients included in this study and compared these reference values with those calculated via conventional methods (data from non-SSI patients).

Results: According to the e-norms method, the normal WBC count was 10.8±1.2 (x10^9/L), neutrophils count was 8.7±1.1 (x10^9/L), lymphocyte count was 1.6±0.3 (x10^9/L), CRP concentration was 31.2±10.8 mg/L, and ESR was 23.6±4.7 mm/h. The mean values obtained via the e-norms and conventional methods were almost identical, but the range of normative reference values obtained via the conventional methods was relatively wider. Importantly, the frequency of SSI patients with abnormal inflammatory markers identified by the e-norms method was higher than that of patients with abnormal inflammatory markers identified by the conventional methods (21/28, 75.0% vs. 6/28, 21.4%; p<.05).

Conclusions: The results of this study demonstrated that the reference values retrieved using e-norms were more effective for screening postoperative SSI than the reference values calculated using conventional methods. Thus, e-norms may be an alternative reliable and time-saving approach to establishing reference values for acute-phase inflammatory markers after spinal surgery.