[Question #7999] Reliability of EIA
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50 months ago
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UK based question. Several high risk oral-based encounters 7 years ago roughly. Thought nothing of it at the time however did have from memory a bad rash on both inner thighs which was very red and itched/burned. I also have the scar of what I thought had been a mouth ulcer on my lower lip, quite large and circular, can still feel the mark. Got a full panel ran via postal order 3 years ago (4 years after event) and came back negative for all but Syphilis positive, apparently by EIA. This was fingerpick blood. Went to GUM clinic at NHS and results came back negative, however I am not sure which test they used. Had 3 subsequent rapid point of care instant tests (Nal Von Minden NADAL tests, all came back negative. All tests taken more than several years after possible exposure. My question is do you feel the negative NHS test coupled with the negative instant tests would likely be more reliable than the previous positive? I have read that the POC tests decline in sensitivity with lower tires in later years. I have also heard that the NPV of tests are usually higher than PPV? Any advice would be greatly appreciated.
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H. Hunter Handsfield, MD
50 months ago
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Welcome to the forum. Thanks for your confidence in our services.
Collectively, the HIV blood tests -- including those using enzyme immunoassay (EIA) technology -- are among the most accurate diagnostic tests every developed, for any medical condition. Among other things, they are highly automated and have been made virtually foolproof. In addition. the NHS GUM clinics have a very strongly positive worldwide reputation for scientific quality and reliability. I am unaware of data on decline in test sensitivity (or a resulting change in the negative predictive value) with longstanding HIV infection.
In addition, you describe low risk exposures, since HIV is almost never transmitted by oral sex. Further, your symptoms are not actually very typical of HIV.
Accordingly, I am confident you can rely 100% on the negative results you have had, especially since you have had several tests by different manufacturers. There is no possibility you have HIV (unless, of course, you have had a potentially risk exposure since your last negative HIV test).
I hope these comments are helpful. Let me know if anything isn't clear.
HHH, MD
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50 months ago
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Hi Dr Handsfield, thank you very much for your reply. I’m afraid I have made an error and misled you - it was syphilis that came back positive on my mail return EIA and then subsequently negative from the NHS test and the rapid POC tests. All happening a number of years after possible exposure? Sorry for not being clear first time. Thanks again
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H. Hunter Handsfield, MD
50 months ago
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My apology! I entirely missed the syphilis business -- I scanned your question too quickly, and except for missing that part, your questions could well have applied to HIV. Apologies again -- my fault, not yours.
The EIA syphilis tests have a high rate of false positive results, and in your case, that's almost certainly what's going on. However, the rapid syphilis blood tests are not normally considered conclusive in evaluating or confirming the syphilis EIA tests, at least not in the US. Perhaps there are data -- in UK or elsewhere -- of which I am unaware. But the normal approach in someone with positive EIA, at least in the US, would be a classical "nontreponemal" test (VDRL or RPR) AND a treponema-specific test like FTA-ABS, TPPA, or a few others. It seems likely your GUM clinic is following standard procedures and recommendations, and I think there is almost no chance you have syphilis. But you might discuss this alternative approach with them. But in the meantime, I really do not think you should be worried about syphilis.
Apologies again for the misunderstanding. I'll be intersted to hear what you learn on re-discussion with your GUM clinic.
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50 months ago
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Thank you once again Dr Handsfield, your advice has really helped settle me.
Final question, if it is allowed - would you imagine the EIA is just as accurate after potentially 7+ years since exposure and is it rare to have a false negative EIA test?
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H. Hunter Handsfield, MD
50 months ago
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The syphilis EIA tests are relatively new and to my knowledge there has been no research on how long false positive results might persist. However, false negative tests are generally believed to be nonexistant. I'm unaware of any reports of persons who had syphilis and whose EIA result was negative, at any time after acquiring syphilis.
On further reflection, I really don't think you need the additional tests i mentioned. Having had several additional POC tests (which are probably equivalent to the EIA tests in performance), I think you can put syphilis out of your mind. You might still discuss additional tests (e.g. RPR, TPPA) with the GUM clinic, but if they are confident such testing isn't necessary, you should accept that advice.
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