valuable and complex risk score based on twelve parameters, including, among others, age, gender, diabetes mellitus, hypertension, and chronic lung disease. Since knowing the risk of clinical deterioration can assist medical decisions about appropriate level of care, predictive models for COVID-19 are becoming notably frequent. However, many of them are notably biased, non-validated, or present a construction lacking in clarity [2, 3] . Moreover, they often conclude that male older patients with comorbidities are more likely to experience unfavourable outcomes [4, 5] , even when such determinants are already well-known predictors of worse result in community-acquired pneumonia [6] . Although the medical assessment of patients must always address demographics and underlying comorbidities, it is known that the evaluation of disease severity and prognosis should not only depend on the above-mentioned risk markers.
Our aim was to help clinicians rapidly identify which patients, attended for the first time in an emergency room and regardless of their age, sex, or comorbid conditions, are more likely to be transferred to the intensive care unit (ICU) or to die, and are therefore candidates for a close monitoring and for the administration of the best available therapy. Thus, we focused on the simplest and readily available hemodynamic and laboratory features to build a quick prognostic equation that, based on five independent predictors, was able to estimate the probability of ICU admission or death among adult COVID-19 inpatients.
Briefly, we conducted a prospective cohort study in Virgen del Rocío University Hospital, a Spanish tertiary-care-teaching centre, where 244 consecutive patients, diagnosed of COVID-19, were enrolled from February 21 to April 8, 2020, and followed-up for 28 days. Data were recorded at the emergency room or upon hospital admission. Primary endpoints were favourable (disease improvement, full recovery and discharge, and/or maintenance of non-critical status) and unfavourable (death and/or ICU admission) clinical outcomes. The study protocol was approved by the Ethics Committee (C.I. 0771-N-20) and complied the Declaration of Helsinki. Further information on study design, statistical approach, and internal validation is provided in the Supplementary materials text, Supplementary Table S1, and Supplementary Table   S2 .
Patients' characteristics are shown in Table 1 . One-hundred-thirty-two (54.1%) were male and median age was 64 (IQR 55-76) years. Older, institutionalized, solid organ transplant recipients, and hypertensive patients were more likely to develop an unfavourable clinical outcome. Dyspnoea, diastolic hypotension, tachycardia, tachypnoea, low peripheral capillary oxygen saturation (SpO2), chest bilateral infiltrates, high qSOFA and CURB-65 scores were also closely linked to a worse prognosis. Leucocytosis, neutrophilia, lymphocytopenia, thrombocytopenia, and high values of neutrophil-to-lymphocyte ratio, C-reactive protein (CRP), ferritin, lactate dehydrogenase (LDH), d-dimer, creatinine, and aspartate aminotransferase were more frequent in the unfavourable outcome group. Forty-three (17.6%) patients were admitted to the ICU. The occurrence of ICU transfer by age-group was: <50 years, n=6 (15.4%); 50-64 years, n=17 (20.0%); ≥65 years, n=20 (16.7%). Overall mortality rate (12.7%) and short-term mortality distribution are described in Supplementary Figure   S1 .
Twenty-three categorical variables were identified as potential independent predictors of unfavourable outcome in univariable logistic regression analysis (Supplementary Table S3 ). We found significant differences between the survival functions of SpO2 <95% (log-rank, p<0.003) and CRP ≥100 mg/L (p=0.015), and the adjusted Cox regression analysis showed that hypoxemic patients and those presenting high CRP were indeed more likely to die earlier (Supplementary Figure S2 ). The prognosis model was composed of five predictors, demonstrated as independent risk factors in the adjusted multivariable logistic regression analysis: SpO2 <95%, neutrophil count >7.5 x10 9 per L, platelet count <130 x10 9 per L, LDH ≥300 UI/L, and CRP ≥100 mg/L (Supplementary Figure S3 ). A final model description, its overall apparent performance, and the explanation on how to implement it are presented in Table 2 .
Unlike the rest of prognosis models published [1, 3, [7] [8] [9] , that included already wellestablished and globally accepted clinical predictors of severity [6], we opted for incorporating exclusively the explanatory variables that were directly related to the pathogenesis of COVID-19. In this respect, the biological plausibility of hypoxemia, thrombocytopenia, neutrophilia, and high levels of LDH and CRP, coupled with their important role in disease progression, make our selected variables of great interest for further research on SARS-CoV-2 damaging mechanisms and therapeutic targets.
Hypoxemia and high LDH, expression of tissue damage, contributed to build Ji et al., Liang et al. and Galloway JB et al. predictive tools [1, 7, 9] . Gong et al. and Galloway JB et al., like us, included CRP and neutrophil count as inflammation markers in their model, but in conjunction with other not as easily accessible predictors, like albumin [1, 3] . The low platelet count, despite its likely interlinkage with thrombosis in the pathogenesis of COVID-19, has not yet been thoroughly explored. Zhao et al. discussed the tendency of these cells to decrease in critically ill patients [10] . Our study goes one step further and offers thrombocytopenia at the moment of hospital admission as a main predictor for short-term adverse clinical outcomes.
In conclusion, we derived and validated a prognostic model, including five common features obtained in the first patient's evaluation at the emergency room, with high sensitivity and specificity to discriminate individuals that might develop critical disease or die, from those with a favourable course. This model, besides the complete clinical evaluation of the patient by the physician, could be helpful for guiding prompt decisionmaking, improve the management of COVID-19 patients, alleviate insufficiency of medical resources, and reduce mortality. 
None.
Not applicable. 
Data are available on request.
The study protocol was approved by the Ethics Committee of Virgen Macarena and Virgen del Rocío University Hospitals (C.I. 0771-N-20) and complied the Declaration of Helsinki.
All authors have approved the manuscript and its publication.
Supplementary material associated with this article can be found in the online version. 