“Old rules for old tests”


I have been looking recently at the various merits of Mantoux testing versus the newer Interferon Gamma Release Assays (IGRAs) for the diagnosis of latent TB infection. Whilst the IGRAs (such as T -spot and Quantiferon Gold) are not perfect by any stretch of the imagination they still seem to have difficulty replacing the long entrenched Mantoux test.

The Mantoux test, which has been in existence for well over a hundred years suffers from various problems. False negatives due to immunocompromise, false positives after BCG, inter-observer variability in measuring the results, and the logistics of administration, just for starters.

One wonders if Mantoux were a new test invented today, whether a test with so many deficiencies and subjectivity would get anywhere near the commercial market. The validation requirements for new tests as stipulated by accreditation agencies are much stricter now than they were 100 years ago, 50 years ago, or even 20 years ago.

I think we are applying old rules for old tests to a certain extent. Mantoux testing is an institution, a tradition, and is what a lot of us are used to. However because it was acceptable testing in previous generations does not mean it is acceptable by today’s standards.

I don’t think IGRAs will need to improve too much more before Mantoux testing ends up as a historical test, and PPD is kept in museums and not laboratories….


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