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Why is there a RIBA indeterminate ?
Jun 16, 2004

Hello Dr.

I have a question that doesn't seem to be answered anywhere on the web, or in this forum. It is a general question for Indeterminate results.

Currently, the criteria for RIBA+ is 2 or more antigen need to react.

Why is there a RIBA indeterminate choice?

What could make only one antigen react?

I would assume if any react, it is positive. If none react, it is negative.

But... somehow..something made the test makers set 2 or more as the criteria.


Response from Dr. McGovern

Your question is a very good one. The answer lies in testing sensitivity and specificity as with all kinds of testing.

Whenever an assay is being tested, each marker is examined to see which ones are positive and which ones are negative in a patient who has true infection and in healthy controls without the infection. The number of markers selected is found after thorough testing of an assay. You want to identify the most patients possible with a true condition (sensitivity of a test), but you don't want to identify controls as having a condition when they don't have it (specificity of a test).

Patients can have reactivity to one band which is totally non-specific and not diagnostic of a particular condition. Therefore, you want to require that a certain number of bands be present to make an accurate diagnosis.

This concept is true for all assays, ie. the same reasoning holds true for Western blot testing for HIV.

I hope this answer clarifies things for you. Dr. McGovern

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