BackgroundSevere acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection affects and alters various laboratory parameters that are predictors of disease severity and mortality, and hence, their prompt identification can aid in patient triaging and resource allocation.ObjectivesA retrospective study was conducted on 7416 admitted coronavirus disease 2019 (COVID-19) patients from 20 March 2020 to 9 August 2021 to identify crucial laboratory biomarkers as predictors of disease severity and outcome; also, their optimal cutoffs were also calculated. A comparison of laboratory markers between both COVID-19 waves was also performed.ResultsThe majority of patients had mild disease (4295/7416, 57.92%), whereas 1262/7416 (17.02%) had severe disease. The overall fatal outcome was reported in 461 (6.22%) patients. Predictors for mortality were age (>52 years), albumin/globulin (A/G) ratio (≤1.47), chloride (≤101 mmol/L), ferritin (>483.89 ng/mL), lactate dehydrogenase (LDH) (>393 U/L), procalcitonin (>0.10 ng/mL), interleukin-6 (IL-6) (>8.8 pg/mL), fibrinogen (>403 mg/dL), international normalized ratio (INR) (>1.18), and D-dimer (>268 ng/mL). Disease severity predictors were neutrophils (>81%), lymphocyte (≤25.4%), absolute lymphocyte count (ALC) (≤1.38×103/µL), absolute eosinophil count (AEC) (≤0.03×103/µL), total bilirubin (TBIL) (≥0.51 mg/dL), A/G ratio (≤1.49), albumin (≤4.2 g/dL), ferritin (≥445.4 mg/dL), LDH (≥479 U/L), IL-6 (≥28.6 pg/mL), C-reactive protein/albumin (CRP/ALB) ratio (≥1.78), D-dimer (≥237 ng/mL), and fibrinogen (≥425 mg/dL). The majority of patients admitted in the second wave were older and had severe disease, increased fatality, and significantly deranged laboratory parameters than first wave patients.ConclusionOur findings suggested that several biomarkers are crucial for both severe disease and mortality in COVID-19 patients. Ferritin, LDH, IL-6, A/G ratio, fibrinogen, and D-dimer are important biomarkers for both severity and mortality, and when combined, they provide valuable information for patient monitoring and triaging. In addition to these, older age, INR, chloride, and procalcitonin are also significant risk factors for mortality. For severe COVID-19, TBIL, CRP/ALB, albumin, neutrophil percentage, lymphocyte percentage, ALC, and AEC are also important biomarkers. According to the study, the majority of the baseline laboratory parameters associated with COVID-19 mortality and severe disease were significantly higher during the second wave, which could be one of the possible causes for the high mortality rate in India during the second wave. So, the combination of all these parameters can be a powerful tool in emergency settings to improve the efficacy of treatment and prevent mortality, and the planning of subsequent waves should be done accordingly.