Preoperative lymphopaenia, mortality, and morbidity after elective surgery: systematic review and meta-analysis

Background: In the general adult population, lymphopaenia is associated with an increased risk for hospitalisation with infection and infection-related death. The quality of evidence and strength of association between perioperative lymphopaenia across different surgical procedures and mortality/morbidity has not been examined by systematic review or meta-analysis. Methods: We searched MEDLINE, Embase, Web of Science, Google Scholar, and Cochrane databases from their inception to June 29, 2020 for observational studies reporting lymphocyte count and in-hospital mortality rate in adults. We defined preoperative lymphopaenia as a lymphocyte count 1.0-1.5x10(9) L-1. Meta-analysis was performed using either fixed or random effects models. Quality was assessed using the NewcastleeOttawa Scale. The I-2 index was used to quantify heterogeneity. The primary outcome was in-hospital mortality rate and mortality rate at 30 days. Results: Eight studies met the inclusion criteria for meta-analysis, comprising 4811 patients (age range, 46-91 yr; female, 20-79%). These studies examined preoperative lymphocyte count exclusively. Studies were of moderate to high quality overall, ranking >7 using the Newcastle-Ottawa Scale. Preoperative lymphopaenia was associated with a threefold increase in mortality rate (risk ratio [RR]=3.22; 95% confidence interval [CI], 2.19-4.72; P<0.01, I-2=0%) and more frequent major postoperative complications (RR=1.33; 95% CI, 1.21-1.45; P<0.01, I-2=6%), including cardiovascular morbidity (RR=1.77; 95% CI, 1.45-2.15; P<0.01, I-2=0%), infections (RR=1.45; 95% CI, 1.19-1.76; P<0.01, I-2=0%), and acute renal dysfunction (RR=2.66; 95% CI, 1.49-4.77; P<0.01, I-2=1%). Conclusion: Preoperative lymphopaenia is associated with death and complications more frequently, independent of the type of surgery.