[Question #2856] Trepenomal vs Non-Trepenomal... and false negatives

41 months ago
So here's my question:

I have unexplained unilateral hearing loss, and my ENT is ruling out a bunch of causes. He ordered a panel of tests... for autoimmune disorders, Lyme and the "Trapenoma Pallidium Confirm" test, which I presume is a Trepenomal test for Syphilis.

In December 2016 and July 2017 I tested negative for full STD panel at my local health clinic. Is it possible under ANY circumstance for both of those tests to have been false-negatives? As I understand they were non-trepenomal.

Also, can you explain the "hook effect" issue that allows for false negatives in some cases?

Around the time I took the 2016 test, I had flu-like symptoms and a rash on my hands and feet. My doctor thought it was foot-and-mouth disease and to be sure I went and had the STD panel and it was negative. Is it possible that was a false reading?


H. Hunter Handsfield, MD
H. Hunter Handsfield, MD
41 months ago
Welcome back to the forum. Sorry to hear about your hearling problem.

Indeed, your doctor has ordered a syphilis blood test. That's routine in evaluating any patient with unexplained hearing loss, especially if the problem is believed to have a neurological origin. For several reasons, however, it is unlikely syphilis is the problem. Syphilitic hearing problems usually are bilateral. They occur predominantly in people with late syphilis, i.e. more than a year in duration. While neurosyphilis can occur within weeks, it is uncommon. Cunnlingus is a low risk exposure in regard to syphilis, even though your partner was bisexual (and syphilis is common in gay men), and if you had acquired syphilis from the oral sex exposure, most likely you would have noticed the primary lesion (chancre) in the exposed area (vulva, vaginal opening, labia, etc). And your "full STD" lab panels almost certainly included syphilis blood tests.

I have never heard of the "hook effect", but googling it reveals this as an occasional name for the prozone phenomenon. (To my knowledge, it is unrleated to my colleague Dr. Hook or his father, who also was a nationally prominent infectious diseases experts.) Prozone results in false negative results with some kinds of syphilis blood tests. However, there are two reasons you can be sure your previous negative syphilis blood tests were accurate. First, syphilis testing the past decade or so has been done almost entirely by IgG ELISA, a test technology that has no prozone problem. Second, even the tests susceptible to prozone ("nontreponemal" tests like RPR and VDRL) cause no problem because almost all labs take steps to prevent it.* Also, viral infections of the sort you apparently had at the time of that STD panel are not known to affect the reliability of syphilis testing.

Having said all that, syphilis is often a mysterious disease, and atypical cases are common. So I think it was wise of your ENT to think of syphilis to evaluate your hearing loss, and there is perhaps a very slim chance syphilis is responsible. But I doubt it very much, and expect your new blood test to also be negative.

I hope these comments have been helpful. Let me know if anything isn't clear, and please return to let me know the result when your new syphilis test result is available.

HHH, MD

* I don't know how much you want to get into the weeds on test technologies. In case you're into the details, the nontreponemal tests (RPR, VDRL) are done by titer -- i.e. if positive, increasingly dilute specimens of serum are retested. If positive undiluted and at dilutions of 1:2, 1:4, and 1:8 but negative at 1:16 and above, the result is recorded as positive in a titer of 1:8. Sometimes active syphilis can give titers as high as 1:256 or even more. Prozone occurs when the undiluted specimen is negative, and yet more diluted serum samples are actually positive. Knowlegeable labs routine avoid prozone by always testing diluted as well as undiluted serum. As a result, prozone is essentially a thing of the past. I've never heard of it occurring in the past 30 years or so.
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41 months ago
Thanks so much for such a detailed response. One more for you:

I checked the urgent care where I had both tests. They confirmed the testing was non-trepenomal. Is there any likelihood I would test negative twice in a year using that nonspecific method, and then test positive in the more specific test?
H. Hunter Handsfield, MD
H. Hunter Handsfield, MD
41 months ago
Almost no chance. But let's wait for that test result before we discuss any further.---