Background: The prognostic role of low postoperative serum albumin levels (SAL) after cardiac surgery (CS) remains unclear in patients with normal preoperative SAL. Our aim was to evaluate the influence of SAL on the outcome of CS.

Methods: Prospective observational study. Patients undergoing CS with normal preoperative SAL and nutritional status were included and classified into different subgroups based on SAL at 24 h after CS. We assessed outcomes (i.e., in-hospital mortality, postoperative complications and long-term survival) and results were analyzed among the different subgroups of SAL.

Results: We included 2818 patients. Mean age was 64.5 ± 11.6 years and body mass index 28.0 ± 4.3Kg·m^- 2 . 5.8%(n = 162) of the patients had normal SAL levels(≥35 g·L^- 1 ), 32.8%(n = 924) low deficit (30-34.9 g·L^- 1 ), 44.3%(n = 1249) moderate deficit (25-29.9 g·L^- 1 ), and 17.1%(n = 483) severe deficit(< 25 g·L^- 1 ). Higher SAL after CS was associated with reduced in-hospital (OR:0.84;95% CI:0.80-0.84; P = 0.007) and long-term mortality (HR:0.85;95% CI:0.82-0.87;P < 0.001). Subgroups of patients with lower SAL showed worst long-term survival (5-year mortality:94.3% normal subgroup, 87.4% low, 83.1% moderate and 72.4% severe;P < 0.001). Multivariable analysis showed higher in-hospital mortality, sepsis, hemorrhage related complications, and ICU stay in subgroups of patients with lower SAL. Predictors of moderate and severe hypoalbuminemia were preoperative chronic kidney disease, previous CS, and longer cardiopulmonary bypass time.

Conclusions: The presence of postoperative hypoalbuminemia after CS is frequent and the degree of hypoalbuminemia may be associated with worst outcomes, even in the long-term scenario.