Point-Counterpoint: Should Interferon Gamma Release Test become the standard method for screening patients for Mycobacterium tuberculosis infections in the United States?

A provocative title for an important debate

The Centers for Disease Control and Prevention have recently published updated guidelines for the use of Interferon Gamma Release Assays (IGRA) to detect Mycobacterium tuberculosis. This document gives a balanced analysis of the strengths and weaknesses IGRAs. To date, these assays have not been widely adopted in the United States by clinical laboratories. In this Point-Counterpoint we have asked two experts, Thomas Alexander of Summa Health Care who has adopted an IGRA for M. tuberculosis detection in his laboratory and Melissa Miller of UNC Hospitals who evaluated one but has not chosen to adopt it to explain how each reached this decision based on their experience with the test and the data that has been published concerning IGRA.

Skipping to the end bits; Summa Health Care*

In conclusion, the advantages of IGRA tests is that they offer increased convenience, sensitivity and specificity when compared to TST. While the test is more expensive than the TST, the use of an IGRA assay in appropriate clinical situations can reduce the overall cost to the health care system and lower the potential morbidity associated with treating many patients with positive TST due to exposure to non tuberculous mycobacteria.

and UNC Hospitals

for the routine implementation of IGRAs for detecting LTBI and active TB in our low
prevalence population with low rates of BCG vaccination and for the screening of HCWs, we will await more compelling data to indicate the sensitivity and/or PPV of the IGRAs are superior to well-performed TST before investing the resources needed to replace TST with an IGRA institution-wide.

The author then lists the points of agreement, which I have abbreviated;

1. There is no diagnostic gold standard for LTBI
2. IGRA have very specific advantages over TST.
3. Both IGRA and TST have technical challenges in both performance and in interpretation
4. IGRA is more expensive for the laboratory.

and issues that need to be resolved

1. lack of good longitudinal studies with IGRA
2. Is IGRA cost justifiable in a low incident population?
3. the effect of multiple prior TST is on the accuracy of IGRAs.
4. The interpretation of IGRA in HIV infected patients with CD 4 counts of less than
200/ul appears to be as problematic as the interpretation of TST.

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It's my opinion that adopters of QFT are happy with their decision whilst those who continue with the TST continue to be dissatisfied. At the 2010 AGM Cellestis attempted to classify these customer related marketing challenges;

– Some customers are simply very slow to change
– Some will find reasons not to change
– Latent TB is not the front of mind priority for many customers
– Perception of cost remains a factor despite realities


 * Summa Health Care is a multi $Billion business