The role of the neutrophil–lymphocyte ratio for pre-operative risk stratification of acute kidney injury after tetralogy of Fallot repair

Introduction: Acute kidney injury is a risk factor for chronic kidney disease and mortality after congenital heart surgery under cardiopulmonary bypass. The neutrophil–lymphocyte ratio is an inexpensive and easy to measure biomarker for predicting outcomes in children with congenital heart disease undergoing surgical correction. Objective: To identify children at high risk of acute kidney injury after tetralogy of Fallot repair using the neutrophil–lymphocyte ratio. Methods: This single-centre retrospective analysis included consecutive patients aged < 18 years who underwent tetralogy of Fallot repair between January 2014 and December 2018. The pre-operative neutrophil–lymphocyte ratio was measured using the last pre-operative complete blood count test. We used the Acute Kidney Injury Network definition. Results: A total of 116 patients were included, of whom 39 (33.6%) presented with acute kidney injury: 20 (51.3%) had grade I acute kidney injury, nine had grade II acute kidney injury (23.1%), and 10 (25.6%) had grade III acute kidney injury. A high pre-operative neutrophil–lymphocyte ratio was associated with grade III acute kidney injury in the post-operative period (p = 0.04). Patients with acute kidney injury had longer mechanical ventilation time (p = 0.023), intensive care unit stay (p < 0.001), and hospital length of stay (p = 0.002). Conclusion: Our results suggest that the pre-operative neutrophil–lymphocyte ratio can be used to identify patients at risk of developing grade III acute kidney injury after tetralogy of Fallot repair.