Cost-effectiveness of IGRAs vs TSTs in HCWs

Following on from the important work conducted by Roland Diel (here, here, here and here) comes a study by de Perio et al "Cost-effectiveness of Interferon Gamma Release Assays vs Tuberculin Skin Tests in Health Care Workers". The authors are from the Divisions of Infectious Diseases University of Cincinnati College of Medicine, Cincinnati Veterans Affairs Medical Center and Veterans Affairs Central Office Infectious Diseases Program, Washington, DC. The objective of this study was to compare the cost-effectiveness of 3 strategies for detecting LTBI in new HCWs, namely, the QFT-G, QFT-GIT, and TST.

Diel et al had previously found (in various studies, follow above links) that

screening for tuberculosis by combining tuberculin skin testing and QuantiFERON-TB Gold markedly reduces public health costs compared with tuberculin skin test screening alone. ...QFT is a more accurate indicator of the presence of LTBI than the TST and provides at least the same sensitivity for detecting those who will progress to active TB....The recommendations to use the IGRA in order to verify a positive TST only should be reconsidered.

The de Perio et al study is a Markov model based on actual staff data from the Veterans Health Administration, who conduct between 37,000 and 43,000 pre employment TB skin tests per year.

To our knowledge, this study is the first to assess the cost-effectiveness of IGRAs vs the TST for detecting LTBI in HCWs. We modeled each step of the LTBI screening process, including the probabilities of having the TST read, of needing to do a 2-step TST, and of obtaining an indeterminate QFT test result. Time costs associated with missing work were included to truly reflect a societal perspective. We used QALYs as the effectiveness measure, the standard in cost-effectiveness analyses.

de Perio et al departed from the Diel methodolgy in that they used a meta analysis of available data;

Unlike our study, which pooled sensitivity and specificity data from multiple published studies, they derived QFT-G characteristics from a single study in which the sensitivity estimate was high. Also, they estimated values for TST characteristics instead of deriving them from the literature and measured effectiveness using life expectancy unadjusted for quality.

They explain the advantage to this approach

The publication of more studies,especially regarding the test characteristics of the QFTGIT, would increase the quality and accuracy of future cost-effectiveness analyses.

Importantly, after rigorous analysis they found

that the QFT-G and QFT-GIT strategies are more effective and less costly than the TST, whether or not the HCW has been previously BCG vaccinated.

Our findings are robust and insensitive to changes across a wide range of probabilities, costs, and utility estimates.

Our sensitivity analyses indicate that the IGRA strategies are clinically and economically worthwhile among low- and high-prevalence populations. Our analysis supports the CDC recommendation of use of the QFT-G in HCW screening.

Below are their findings as to costs (click on image for FULL SIZE)