Prevalence of pre-operative anaemia in surgical patients: a retrospective, observational, multicentre study in Germany

Anaemia is a risk factor for several adverse postoperative outcomes. Detailed data about the prevalence of anaemia are not available over a long time-period in Germany. In this retrospective, observational, multicentre study, patients undergoing surgery in March in 2007, 2012, 2015, 2017 and 2019 were studied. The primary objective was the prevalence of anaemia at hospital admission. The secondary objectives were the association between anaemia and the number of units of red blood cells transfused, length of hospital stay and in-hospital mortality. A total of 23,836 patients were included from eight centres. The prevalence of pre-operative anaemia in patients aged ≥ 18 years decreased slightly from 37% in 2007 to 32.5% in 2019 (p = 0.01) and increased in patients aged ≤ 18 years from 18.8% in 2007 to 26.4% in 2019 (p > 0.001). The total amount of blood administered per 1000 patients decreased from 671.2 units in 2007 to 289.0 units in 2019. Transfusion rates in anaemic patients declined from 33.8% in 2007 to 19.1% in 2019 (p < 0.001) and in non-anaemic patients from 8.4% in 2007 to 3.4% in 2019 (p < 0.001). Overall, the mortality rate remained constant over the years: 2.9% in 2007, 2.1% in 2012, 2.5% in 2015, 1.9% in 2017 and 2.5% in 2019. In the presence of anaemia, mortality was significantly increased compared with patients without anaemia (OR 5.27 (95%CI 4.13-6.77); p < 0.001). Red blood cell transfusion was associated with an increased risk of mortality (OR 14.98 (95%CI 11.83-19.03); p < 0.001). Using multivariable linear regression analysis with fixed effects, we found that pre-operative anaemia (OR 2.08 (95%CI 1.42-3.05); p < 0.001) and red blood cell transfusion (OR 4.29 (95%CI 3.09-5.94); p < 0.001) were predictors of mortality but not length of stay (0.99 (95%CI 0.98-1.00) days; p = 0.12) and analysed years (2007 vs. 2019: OR 1.49 (95%CI 0.86-2.69); p = 0.07). Pre-operative anaemia affects more than 30% of surgical patients in Germany and multidisciplinary action is urgently required to reduce adverse outcomes.