Decision analytic modelling to inform policy and research decisions on the use of risk assessment models to select patients at risk of venous thromboembolism for pharmacologic prophylaxis

Pharmacological thromboprophylaxis can be used to reduce the risk of venous thromboembolism (VTE), but it is costly and is associated with an increased risk of bleeding. Selecting higher-risk individuals for thromboprophylaxis using a risk-assessment model (RAM) has the potential to be cost-effective if the population selected has a more favourable balance of costs, benefits and harms.
This thesis discusses the use of decision-analytic modelling to assess the cost-effectiveness of RAM-based prophylaxis in several distinct populations: outpatients having lower limb immobilisation following injury, medical and surgical inpatients, and women who are pregnant or in the puerperium. In each population, RAM-based prophylaxis was compared against prophylaxis for all and prophylaxis for none. The RAMs modelled were those validated for use in each specific population. Where data allowed, the analyses compared alternative RAMs, alternative RAM cut-offs for prophylaxis and the optimal trade-off between RAM sensitivity and specificity in a given population. Cost-effectiveness was assessed by comparing lifetime costs and quality-adjusted life years from an NHS and personal social services perspective.
The cost-effectiveness of RAM-based prophylaxis varied across the populations considered due to differences in the risks of VTE and the differences in the prognostic accuracy of the available RAMs. In postpartum women, RAM-based prophylaxis was not cost-effective compared to no prophylaxis due to the very low risk of VTE and the poor specificity of the available RAMs. In people having lower limb immobilisation, a RAM would need to have a sensitivity of between 84% and 89% and a specificity of between 46% and 55% for RAM-based prophylaxis to be cost-effective. Whereas in medical and surgical inpatients, a RAM would need to have very high sensitivity for RAM-based prophylaxis to be more cost-effective than prophylaxis for all. The cost-effectiveness of RAM-based prophylaxis was most uncertain in high-risk antepartum women and obese postpartum women.