Prediction of mortality and prioritisation to tertiary care using the 'OUR-ARCad' risk score gleaned from the second wave of COVID-19 pandemic-A retrospective cohort study from South India

Abstract

Background: Judicious utilisation of tertiary care facilities through appropriate risk stratification assumes priority, in a raging pandemic, of the nature of delta variant-predominated second wave of COVID-19 pandemic in India. Prioritisation of tertiary care, through a scientifically validated risk score, would maximise recovery without compromising individual safety, but importantly without straining the health system.

Methods: De-identified data of COVID-19 confirmed patients admitted to a tertiary care hospital in South India, between April 1, 2021 and July 31, 2021, corresponding to the peak of COVID-19 second wave, were analysed after segregating into 'survivors' or 'non-survivors' to evaluate the risk factors for COVID-19 mortality at admission and formulate a risk score with easily obtainable but clinically relevant parameters for accurate patient triaging. The predictive ability was ascertained by the area under the receiver operator characteristics (AUROC) and the goodness of fit by the Hosmer-Lemeshow test and validated using the bootstrap method.

Results: Of 617 COVID-19 patients (325 survivors, 292 non-survivors), treated as per prevailing national guidelines, with a slight male predilection (358/617 [58.0%]), fatalities in the age group above and below 50 years were (217/380 [57.1%]) and (75/237 [31.6%]), p<0.001. The relative distribution of the various parameters among survivors and non-survivors including self-reported comorbidities helped to derive the individual risk scores from parameters significant in the multivariable logistic regression. The 'OUR-ARCad' risk score components were-Oxygen saturation SaO2<94%-23, Urea > 40mg/dL-15, Neutrophil/Lymphocytic ratio >3-23, Age > 50 years-8, Pulse Rate >100-8 and Coronary Artery disease-15. A summated score above 50, mandated tertiary care management (sensitivity-90%, specificity-75%; AUC-0.89), validated in 2000 bootstrap dataset.

Conclusions: The OUR-ARCad risk score, could potentially maximize recovery in a raging COVID-19 pandemic, through prioritisation of tertiary care services, neither straining the health system nor compromising patient's safety, delivering and diverting care to those who needed the most.

Fig 1. Kaplan-Meier analysis of the parameters significantly attributing to risk of mortality in the univariate analysis.

Kaplan-Meier mean survival estimates for the time to mortality censored at 50 days. The numbers given below denote the number of individuals who were alive at that particular time point in days, with and without the risk factor that is being evaluated. Significance was computed using the log-rank test. SaO₂ –Peripheral oxygen saturation, %—percentage, <—lesser than, mg/dL–milligram per decilitre, NLR–Neutrophil Lymphocyte Ratio, p–p value.

Fig 2. Illustrated depiction of ROC curves of important parameters used in score formulation along with biomarkers.

The relative positions in the ROC curve also provide the precision of parameters, compared to biomarkers, in predicting mortality. ROC Curve—Receiver Operating Characteristic Curve, D-dimer–D protein dimer of Fibrin degradation product, CRP- C-Reactive Protein, SaO₂—Peripheral Oxygen Saturation, NLR—Neutrophil Lymphocyte Ratio, %—percentage.

Fig 3. Decreasing oxygen saturation with corresponding levels of NLR and D-dimer for understanding the interplay of inflammation.

The rising slope of NLR precedes the rise in D-dimer above 1000 ng/mL and corresponding reduction in SaO₂, making it a perfect surrogate for inflammatory biomarkers to dictate the prophecy of COVID-19 prognosis. The cut-off of SaO₂ above 94% as stated in the WHO and national guidelines is ascertained in our cohort when the D-dimer levels are well below 500 ng/mL (negative for in situ thrombosis). NLR–Neutrophil Lymphocyte Ratio, SaO₂ –Peripheral oxygen saturation, D-dimer–D protein dimer of Fibrin degradation product, ng/mL–nanogram per millilitre, <—lesser than, >—greater than.