External validation of improve-DD risk assessment model for venous thromboembolism among inpatients with COVID-19

Background : There is a need to move towards an individualized, risk-adapted approach in order to discriminate higher risk groups for venous thromboembolism (VTE) in hospitalized COVID-19 patients and inform thromboprophylaxis strategies. The IMPROVE-DD VTE risk assessment model (RAM) has previously demonstrated good discrimination in non-COVID populations. Aims : This study aimed to externally validate the IMRPOVE-DD RAM for VTE in a hospitalized, COVID-19 medical population in a large, integrated academic health center. Methods : In this retrospective cohort study, the IMPROVE-DD VTE RAM was evaluated on adult patients with COVID-19 admitted to one of thirteen Northwell Health hospitals in the New York metropolitan area between March 1, 2020 and April 27, 2020. VTE was defined as a new onset deep venous thrombosis or pulmonary embolism, as identified on Radiology Department imaging or pointof-care ultrasound and manually adjudicated by two attending radiologists. To assess the predictive value of the RAM, the receiver operating characteristic (ROC) curve was plotted, and area under the curve (AUC) was calculated. Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were calculated using standard methods. Results : Of the 9,407 patients who met the study criteria, 274 patients developed VTE with a prevalence of 2.91%. The VTE rate was 0.41% for IMPROVE-DD score 0-1 (low risk), 1.21% for score 2-3 (moderate risk), and 5.30% for score ≥ 4 (high risk) (Table 1). Approximately 45.7% of patients were classified as high VTE risk, 33.3% moderate risk, and 21.0% low risk. The RAM discrimination of low versus moderate-high VTE risk demonstrated sensitivity 0.971, specificity 0.215, PPV 0.036, and NPV 0.996. ROC AUC was 0.703 (Figure 1). Conclusions : In this external validation study, the IMPROVE-DD VTE RAM demonstrated very good degree of discrimination to identify hospitalized COVID-19 patients at low, moderate, and high VTE risk.