Introduction COVID- 19 is a disease that has claimed the lives of many people. However, alterations in labo-ratory profiles in the city of Tacna have not been accurately established in association with its severity to support diagnosis and treatment. Objective To determine biomarkers related to the severity of COVID- 19 in patients treated at the social security hospital in Tacna during 2020. Methods We performed an observational, cross- sectional, and analytical study that included 308 patients with COVID- 19 from the social security hospital in Tacna, Peru, during the "first wave" of the pandemic (from July to August 2020). Immunological, hematological, arterial gas, hemostasis, and biochemical markers were collected. Patients were categorized into mild, moderate, and severe based on the clinical criteria found on clinical records. Correlation strength was per-formed according to Spearman’s Rho coefficient. The performance of the biomarkers associat-ed with severity was analyzed with the Receiver Operating Characteristic curve. Results Regarding hematological markers there was a positive correlation with monocyte count (correla-tion coefficient: 0.841; area under the curve 97.0%; p < 0.05) and a negative correlation with lymphocyte count (correlation coefficient: -0.622; area under the curve 82.7%; p < 0.05). Regarding biochemical markers, arterial gases and hemostasis, no significant correlations were found. In immunological markers, we found positive correlation with ferritin (correlation coef-ficient: 0.805; area under the curve 94.0%; p < 0.05), and C- reactive protein (correlation coeffi-cient: 0.587; area under the curve 87.4%; p < 0.05). Conclusions The biomarkers that can be considered as parameters associated with the severity of COVID- 19 are the absolute blood count of monocytes and serum ferritin concentration.