Introduction: Coronavirus disease 2019 (COVID-19) or severe acute respiratory syndrome caused by coronavirus (SARS-CoV-2) was a global pandemic caused by the RNA virus of the beta-coronavirus family. On May 5, 2023, WHO officially announced the end of the pandemic, while people are still infected with the new coronavirus and die from the consequences of this infection. Much attention of scientists is paid not only to the clinical symptoms of the active phase of viral infection and postcoid syndrome, but also to a change in laboratory indicators. The purpose of the study: to study the concentration of total hemoglobin (Hb), red blood cells (RBC) and mean red blood cell volume (MCV) in middle, elderly and senile patients in the covid and post-covid periods. Materials and methods: The study was carried out on the basis of a database of results of laboratory blood tests of patients of the Ariadne laboratory information system of St. Petersburg State Budgetary Institution "GMPB No. 2": 12,838 clinical blood test results (Hb, RBC and MCV) of patients treated in the hospital, who went to the clinic or underwent clinical examination at the hospital during the following periods were studied: dock (01.09.2019 - 31.12.2019), covid (11.11.2020 - 21.02.2021) and post-covid (01.09.2022 - 31.12.2022) periods. Results: From the data obtained, it follows that the hemoglobin concentration in the blood decreased statistically significantly during the covid period in middle-aged patients, increased in elderly people and remained unchanged in senile people. In the postcoid period, an increase in hemoglobin levels was observed in all age groups compared to the values of the covid period. At the same time, in middle-aged people, the indicator returned to the level of the dockoid period, and in elderly and senile people, the concentration of hemoglobin in the blood in the postcoid period significantly increased. Discussion: The impact of COVID-19 and hyperglycemia on human hematology remains understudied, particularly in terms of mean red blood cell volume, hemoglobin concentration, and red blood cell count. Conflicting data are presented in the literature, with the exception of hemoglobin concentration in the blood: it decreased during the period of SARS-CoV-2 infection, remained reduced in the postcoid period or was within the reference interval, decreased in carbohydrate metabolism disorders. The results of our study are correlated with the data of literary sources for the covid period - the hemoglobin concentration decreased in all age groups. Conclusion: Thus, during the study, some facts related to the change in certain hematological indicators during the covid period were confirmed. However, in the post-covid period, the change in two indicators was more characteristic of people with impaired carbohydrate metabolism (increased red blood cell concentration and average red blood cell volume).