What is the significance of index value mentioned in hiv-1/2 & p-24 combo test? I have done a hiv testing with no exposure history ,just for premarital formality. The report clearly mentioned negative/ non-reactive. But it appeared with a index value of 0.259. I want to know what does it mean?

It means negative.

The "index value" (also called the "signal-to-cutoff ratio") is a technical term having to do with how this type of hiv-antibody test is conducted. Values less than 0.90, like yours, are definitively negative! values between 0.9 and 1.0 would be equivocal or borderline. And values above 1.0 would be preliminarily positive. These preliminarily positive (or provisionally reactive) tests require a confirmatory test before someone is told they are hiv positive (infected). However, none of this applies to you, as you are conclusively hiv negative.