Routine blood parameters are altered in patients with COVID-19 with differences depending on the severity of the disease. Therefore, they may predict diagnosis as well as prognosis of patients with COVID-19 and may be helpful when resources are limited.All patients admitted to our hospital were analyzed for routine blood parameters and SARS-CoV-2 screening results on admission. Primary endpoint was the area under the curve (AUC) of the receiver operating characteristic (ROC) analysis of routine

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... blood parameters with PCR as gold standard.A total of 115 patients were included in the study. Median age was 79 years and male/female ratio was 49%/51%. 77 (67%) patients had PCR confirmed COVID-19. The lactate dehydrogenase (LDH) to leukocyte (WBC) ratio was the best diagnostic predictor (AUC 0.82), markedly better than the single parameters LDH (AUC 0.72) and WBC (AUC 0.75). Optimum cut-off of LDH/WBC ratio was 24.7 nU (sensitivity 87%, specificity 76%). The best single parameter for predicting a severe course of COVID-19 patients were CRP (AUC 0.83) and absolute lymphocyte count (ALC, AUC 0.77). Their ratio CRP/ALC surpassed both with an AUC of 0.88. Optimum cut-off was 77 n*mg (sensitivity 83%, specificity 80%).Our study showed, that on admission the LDH/WBC ratio is a diagnostic predictor of COVID-19 in symptomatic patients. In patients with COVID-19 the CRP/ALC ratio predicts severe course and probability of survival. Both are simple and good tools and may be helpful during pandemic when resources are limited.