Predicting Venous Thromboembolism in Primary Care

Abstract

Venous thromboembolism (VTE) is diagnosed in the outpatient setting in at least 70% of the cases 1,2 and prevention of ambulatory cases might substantially contribute to a reduction of its socio-economic burden. 3,4 Notwithstanding, as we enter the second decade of this millennium, the evidence that was generated after decades of clinical research remains unable to support decision-making beyond in-hospital thromboprophylaxis. Clearly, the exposure to major risk factors for thrombosis is highest during hospitalisation, and this is when the highest absolute rates of VTE are observed. Prophylactic anticoagulation is, therefore, routinely recommended based on the usually favourable benefit-to-risk ratio in this setting. 5 On the other hand, if we turn our attention to primary VTE prevention in the non-hospitalised population, only selected patient groups with active cancer have been targeted by clinical trials in view of their substantial baseline risk of developing VTE. 6,7 Although the VTE risk of individuals without cancer might also suffice for considering primary thromboprophylaxis in primary care, current evidence falls short of quantifying this risk and reliably identifying patients who may benefit from pharmacological preventive strategies.In this issue of Thrombosis and Haemostasis, Dentali et al make a new attempt to identify predictors of VTE in primary care. 8 Their risk assessment model was derived using data from a large Italian database of more than one million adults followed by 1,100 general practitioners. After derivation and internal validation, they performed external validation in an independent cohort used by local authorities for health care assessment. The analysis was conducted as a nested casecontrol study, where VTE diagnoses were defined by a combination of International Classification of Diseases-9th Edition codes. Control patients who did not develop VTE during samelength follow-up were randomly matched to VTE cases within each risk set. The main finding of the study by Dentali et al is that patients who had recently been hospitalised, admitted to the emergency room, or had suffered fracture, stroke, acute infection, or prior VTE, had an at least twofold higher risk of suffering VTE during follow-up. To make their risk assessment model more practical and facilitate clinical decisions, the authors went further by developing a classifier for patients into the different risk categories.In a world where new clinical scores are constantly developed, published, and then frequently discarded as clinically irrelevant, the authors must be commended for scrutinising their risk assessment model by determining its discrimination, calibration and potential clinical benefit if it were to be used for thromboprophylaxis. 8 For the readers who are not familiar with these parameters, discrimination corresponds to the probability of correctly classifying patients into those who will and those who will not have the outcome, in this case VTE. Discrimination alone, however, has no clinical utility and is a p...