How do I undersand an out of range EIA Value for Herpes Simplex type 2?

Question

I recently went to the Dr. He told me I tested negative for Herpes Simplex type 2. However, when I look at the test results, there is nothing in the in range column, but the out of range column shows >5.0 What does this mean. When looking at the explanations of the EIA test results it says anything >1.1 is positive and a 5.00 is certainly greater then 1.1. So why would the Dr. say I was negative and did not have the herpes virus? Is there a diference between in range and out of range test results that I am not understanding?

Answer 1

It depends on how the test is made. EIA tests work by placing a sample of diluted plasma in a well with a plastic bead that is covered with the antigen found on the virus the test is looking for. If the person providing the sample is positive, the antibodies in their blood will bind to the antigen on the bead. If there are no antibodies present, nothing will happen.

Here's where it gets a little complicated. Most EIA tests are non-competitive. The sample is incubated with the bead for a while, then the bead is washed. Then a conjugate is added, which will bind to any antibodies that have bound to the bead. Again, if no antibodies were present, nothing happens. The bead is washed again, and a substrate is added. If there is a conjugate-antibody-antigen sandwich present, the whole thing turns yellow. The more of that sandwich that is there, the darker the color will be. When it is read by a spectrophotometer, the intensity of the color is given a numerical value. The higher the number, the more positive the result.

However, some EIA tests are competitive. They are basically the same as non-competitive tests, except the conjugate is added at the same time as the sample, and binds directly to the antigen instead of the antibody. If there are antibodies present, they will bind to the bead, leaving less room for the conjugate to bind. The more antibodies present, the less conjugate will bind, and when the bead is washed, if no conjugate could bind to the bead, it will all get washed away. When the substrate is added, only the conjugate will make it change color. If no conjugate is bound to the bead (because a lot of antibodies were present), no color will develop. In this kind of EIA test, a lower number indicates a positive, and a higher number indicates a negative.

Your doctor undoubtedly knows how to interpret the results of these tests, and if he said you were negative, it's likely the test was the second kind, and you were not only negative, you were *very* negative.  

Answer 2

Good question.