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Recent NICE guidance for the diagnosis of angina provides a framework for the selection of the most cost effective tests based on the level of risk a patient represents. This risk stratification approach to diagnostic test selection presents a substantial change to the current service provision in the South West of England. In current service provision, for example, the majority of patients initially undergo a exercise tolerance test (ETT) on a treadmill and based on the result and other clinical information may then go on to further testing such as invasive angiography (IA). NICE recommends that ETT is no longer used as part of a diagnostic pathway and instead the use of tests such as IA should be initially decided upon by clinical history alone.
If implemented, the impact of these changes on costs, diagnostic outcomes and adverse events (such as complications from IA) will vary depending on local population demographics, prevalence of coronary artery disease and the extent to which the NICE guidelines are implemented. In order to assess these costs and consequences some prospective evaluation of changes is required.
PenCHORD worked with the South West Peninsula Cardiac Network lead to develop a tool to compare cost, overall diagnostic accuracy, adverse events and uncertainty in these estimates between two competing diagnostic pathways. As current practice, costs, and the extent of implementation vary across the trusts in the network, the tool was designed to be generic and reusable. Users of the tool are able to enter the following parameters:
The final input parameter provides flexibility to use the cost-consequence tool in any trust. Users are able to select which first line diagnostic tests are applied to different groups of the population by risk level and which, if any, second and third line tests are applied depending on positive and negative test outcomes.
Driving the outputs of the tool is a decision tree model that pushes the same population of patients through two different diagnostic pathways. As there is considerable uncertainty in the majority of input parameters, Monte-Carlo simulation is used to quantify the likely range of costs and consequences that might be expected under the differing pathways.
To allow use of the tool by the NHS, PenCHORD implemented the tool in Microsoft Excel. Users follow a simple setup wizard to input data and run the model. The tool is also set up to work in a group meetings and provides a 'discussion mode' where users can quickly run the model, note outputs, make small changes to input variables (for example, the proportion of patients undergoing ETT as a first line diagnostic test), and quickly see the impact on the results. In this way the tool aims to provide a framework to aid users think through what data are needed to evaluate pathway changes and how different factors affect costs and consequences.