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Clarification please
Nov 9, 2009

Hi Dr. Bob! BTW, you are just the BEST =) My ? is this? I had a pos ELISA and Neg WB 3wks after possible exposure and I am retesting in 11 days (13 wk mark) Ive read that the ELISA is extremely sensative and the WB is a conf test, but because the ELISA is so sensative, does that mean that it can detect the HIV antibodies faster than (or sooner than the WB).

Thank you for your time Dr. Bob. Take care of yourself.

Worried76

Response from Dr. Frascino

Hello,

The ELISA test does not detect HIV antibodies faster or sooner than a Western Blot test. The terms "sensitivity" and "specificity" when referring to test accuracy can be confusing. See below for a brief discussion of differences.

Good luck with your upcoming test.



Dr. Bob

testing (SENSITIVITY VERSUS SPECIFICITY) Feb 9, 2008

On previous posts you say that the western blot test is more sensetive and other informaton that I have read says it is the more specific test. What is the difference between the western blot and the elisa test? Thank You

Response from Dr. Frascino

Hi,

You are correct. I was using the word sensitive in its generic sense. That is trying to reassure the questioner that the Western Blot was the test to rely on to confirm a positive ELISA or determine the ELISA was falsely reactive.

The technical terms sensitivity and specificity are defined below:

The specificity is the number of true negatives (disease-free) divided by the number of all negative cases in the population.

The sensitivity is the number of true positives (with disease) divided by the number of all positive cases in the population.

Consequently, using the technical definitions, what you read is correct. Western Blot (WB) tests would be more "specific." They would be able to determine "true negatives" better than an ELISA, which is more sensitive (i.e. able to determine more true positives than the WB).

Hope that helps. I know it's a bit confusing.

Dr. Bob



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