Association of hemoglobin level at admission with postoperative pneumonia in elderly patients with hip fracture: a retrospective cohort study

Abstract Background and Aim Postoperative pneumonia (POP) is a common complication in elderly patients with hip fracture. Low preoperative hemoglobin (Hb) levels have shown strong associations with POP including, but the cut-off value of Hb level remains to be elusive. In this study, we investigated the quantitative relationship between preoperative Hb levels and the accidence of POP in elderly patients with hip fracture. Methods This study was a retrospective cohort study. A total of 1444 elderly patients with hip fracture admitted to the Department of Orthopedics, Shenzhen Second People's Hospital from January 2012 to December 2021 were retrospectively included. Demographic and clinical data (including laboratory tests) were analyzed and compared to explore the relationship between Hb level at admission and POP. Results There were 389 males and 1055 females with an average age of 77.55 ± 8.75 years. The incidence of POP in elderly patients with hip fracture was 6.30% (91/1444). The regression equation showed that, without adjustment for covariates, the incidence of POP decreased by 52% (P = 0.0136) and 59% (P = 0.0047) in Q3 and Q4 in comparison to Q1, respectively. After adjusting for confounding factors, a nonlinear relationship was achieved between Hb and pneumonia. Threshold effect analysis showed that the inflection point was 82.3 g/L. On the left side of the inflection point, Hb level was negatively correlated with the incidence of POP (OR: 0.90, 95%CI: 0.84–0.96, P = 0.00178). On the right side of the inflection point, there was no correlation between Hb levels and POP (OR: 1.00, 95%CI: 0.98–1.01, P = 0.7938). Conclusion There is a nonlinear relationship between preoperative Hb level and POP in elderly patients with hip fracture. When the Hb level was lower than 82.3 g/L, the preoperative Hb level was negatively correlated with POP, but when the Hb level was higher than 82.3 g/L, no correlation was observed.