Aim: The coronavirus disease (COVID-19) has been a public health problem that causes severe acute respiratory syndrome affected all over the word since 2019. The most commonly used parameters as inflammatory response in the clinic are leukocytes, neutrophils, erythrocyte amount and serum C-reactive protein (CRP). In recent years, it has been reported that serum PCT (procalcitonin) level may be useful in the diagnosis of bacterial and viral infections. The aim of our study is to compare blood parameters that may play a supportive role to diagnose of COVID-19 in healthy control and critically COVID-19 patient groups. Material and Methods: This retrospective research was carried out in Malatya Turgut Ozal University Training and Research Hospital, Malatya, Türkiye. Total 88 critically ill patients and 90 healthy people accepted to the study and electronic medical records of patients and control group has been collected from hospital information system (HIS). COVID-19 diagnose has been confirmed by real-time polymerase chain reaction (RT-PCR) results. Results: No statistically significant difference was found between the patient and control groups according to gender in the participants included in the study. A statistically significant increase was observed in CRP, LDH, PCT, D-dimer, urea, sediment, lympocyte and neutrophil levels in COVID-19 patients. According to logistic regression analysis CRP, LDH and sediment values were found to be statistically effective in estimating the COVID-19 infection. These results also supported by ROC analysis, CRP, neutrophil, LDH, PCT and D-dimer results were determined to be distinguishing parameters for COVID-19 patients. Conclusion: We found that CRP, PCT and LDH levels higher in the COVID-19 patients and these parameters can be used to diagnose and estimate the prognose of COVID-19 infection in intensive care patients.