Other markers investigated in this population have gained importance in the diagnosis of the disease since the course of COVID-19 disease is atypical in the paediatric population and PCR may be misleading. The leukocyte profile is one of these biochemical tests. Children did not have lymphopenia in hemogram count, whereas relatively neutropenia and monocytosis were detected, unlike the adult population. The reason why children do not have lymphopenia is thought to be due to the fact that the thymus is more active in the first years of life.

Two-hundred and four patients operated in our paediatric cardiac surgery clinic from 11March, 2020 to 1 April, 2021 were retrospectively examined and 11 patients with preoperative asymptomatic and PCR (−), but with PCR (+) in the post-operative period (patients with incubation period or false PCR negativity) were included in our study. Patients requiring emergency operation and operated from PCR (+) patients in the preoperative period were excluded from the study.

The neutrophil ratio in the lymphocytic series of 7 patients out of 11 patients was slightly below the normal range in the preoperative period, the lymphocyte ratio of 3 patients was slightly above the normal range, and the relative monocyte ratio of 10 patients was slightly above the normal range.

We think that evaluating the leukocyte profile combined with RT-PCR will give more accurate results in the diagnosis of incubation period and false RT-PCR negative patients. In addition, we believe that the algorithms for non-complex paediatric cardiac surgery procedures and timing in the paediatric population with a better course of COVID-19 disease with a positive post-operative course.