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Tuesday, October 23, 2007
P3-15
WHAT IS THE APPROPRIATE CUT-OFF FOR B NATRIURETIC PEPTIDE TESTING BEFORE ECHOCARDIOGRAPHY IN DIAGNOSIS OF HEART FAILURE?
Methods: Cost-effectiveness analysis considering investigation costs only with an outcome measure of cases detected.
A decision analytic model compares three strategies for a patient presenting with the symptoms of heart failure. The strategies are no testing, BNP testing followed by echocardiography for those with BNP above a given threshold, and immediate echocardiography.
A diagnostic algorithm based on clinical signs gives a pre-test probability (PTP) that the symptoms are truly reflective of heart failure. An algorithm based on the ROC curve for BNP level converts this to a post-test probability. Cost-effectiveness of echocardiography following the BNP test depends only on post-test probability and the cost of echocardiography.
The full model is required to determine whether it is cost-effective to use the BNP test. At a fixed PTP, the results for different cut-off values of BNP can be plotted as a curve in the cost-effectiveness plane. Comparing this curve with the points representing no investigation and immediate echocardiography determines the range of willingness to pay (WTP) per case detected at which BNP testing is cost-effective for this PTP. Varying the PTP allows one to determine the range of PTP at which BNP testing is cost-effective for a given WTP.
Results: At a PTP of 20% true heart failure, no investigation is cost-effective at a WTP of under £295 ($580) per case detected, while immediate echocardiography is cost-effective at over £2230 ($4400) per case detected. BNP testing is indicated at a WTP between these two limits. The WTP limits at which BNP testing is indicated vary with the PTP.
At an arbitrary WTP of £500 ($990) per case detected, no investigation is cost-effective at a PTP of below 9.7%, while immediate echocardiography is cost-effective at a PTP of above 45%. Between these values, BNP testing should be used, followed by echocardiography when the post-test probability exceeds 22%.
Conclusions: A simple algorithm can be used to determine a PTP of true heart failure. For high PTP, immediate echocardiography is indicated, while for very low PTP, no further investigation is cost-effective.