[Question #6020] Possibility of False Positive VDRl Syphilis Test

18 months ago
Hello,

Just over a week ago I asked a question about an unprotected vaginal and oral encounter that I had with a woman that I knew from years ago but I am not sure about her STD/STI status. I am a male....Anyway my last syphilis test was at VDRL at 6 weeks and 4 days post exposure and it was negative.  I am at almost 9 weeks now since the possible exposure and I would like to test again but I am very nervous about the possibility of a false positive on my new VDRL syphilis test. I will explain why below. I very well may be overthinking this but yet again I am very nervous.

I plan on testing again soon but I am very nervous about potentially getting a false positive syphilis result on my next VDRL blood test. Yesterday I was working on a wooden dock and I suffered some lacerations on my hand from a rope being squeezed on my hand very hard. I worked through the pain and cuts but I am nervous now as my hands were a bit dirty from handling old water logged dock boards and then washing my hands in lake water and also under water from a tap that comes from an unfiltered sisturn/well. The rope also very likely was not all that clean. I am worried about tetanus getting in the small lacerations on my hand either via dirt or the water. On my ground where I was placing the boards there was also some goose dung I noticed. I was pulling nails out of the boards as well and one poked me very lightly but it did not really break the skin at all. I had a tetanus booster shot about 4 years ago but I have read that tetanus vaccine antibodies can effect a syphilis blood test result by giving false positives if they are active? Any advice on what I should do? Should I wait longer to test in case the tetanus antibodies are currently active?
Edward W. Hook M.D.
Edward W. Hook M.D.
18 months ago
Welcome back to the Forum. On this occasion I will be answering your question.  In preparation I have reviewed your interaction with Dr. Handsfield 9 days ago and agree with all that he said.  While I cannot tell you what the penile lesion you noted was, I agree that the exposure was very low risk and that your tests prove that your lesion was not syphilis. 

I do think that you are overthinking this and would add, mostly as an FYI comment that most experts suggest that  tetanus boosters are needed about every 10 years so you may have received a booster you did not need.  

I really see no need for further testing.  With respect to the possibility of a falsely positive test, anything that stimulates the immune system, i.e. another illness, a vaccination, etc. is associated with a VERY small increase in risk for a falsely positive test result however that increment is tiny and not a concern. Most typically, if there is a positive result, standard testing procedures include steps to differentiate a falsely positive test from a test reflecting a true infection.   While I see no need for further testing related to the lesion you described, if you choose to test, I would not worry about a falsely positive test.  

I hope that this information is helpful.  EWH
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18 months ago
Thank you very much Dr. Hook that is indeed helpful. I do have a few more questions though.

1.) So then even though a few days ago I suffered a number of small lacerations on my hand from a dirty rope along with getting some dirt and then quite a bit of water that was not clean filtered water that should NOT increase the chance of a false positive VDRL syphilis test result if I test in 3 days from now?

2.) The tetanus shot that I got about 4 years ago that may be currently active by creating antibodies in relation to the small lacerations on my hand that I described above in my first question should also NOT cause a false positive VDRL sysphilis test result if I test in 3 days from now?
Edward W. Hook M.D.
Edward W. Hook M.D.
18 months ago
Straight to your questions:

1.  Correct, your hand lacerations and the exposure to dirty water in no way increase your risk for a falsely positive VDRL.
2.  Your tetanus booster, recent or four years ago will not affect the results of your VDRL.

Bottom line, please take a deep breath and do your best to relax. I am confident that your follow-up VDRL will once again be negative.  At that time I hope you will be able to put your concerns behind you and move forward.  EWH   
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18 months ago
Thank you again Dr. Hook your answers to my questions are indeed helping me to relax. I do have a few more final questions though.

1.) I work full time in a Nursing Home as a Personal Support Worker and as a result I help people that are not in good health with their daily living routines. Many of them have conditions such as MRSA, Shingles and other diseases. I also clean up faces and urine frequently from incontinent individuals there. I do my best to wear PPE and gloves when needed. Is there much chance of say getting a false positive VDRL Syphilis test from working in an environment like that?

2.) Last night as I was going to bed I felt a slightky itchy and slightly burning like feeling on my leg and noticed a spot that looks like it might be a bug bite. The area in which I was working on the dock 4 days ago is an area that is known to have ticks some of which I have heard carry lyme disease. I am not sure exactly how common lyme disease is there but I have heard that it does exist. I am continuing to monitor that spot on my leg. Right now it feels at some points like it is slightly burning. It could be my mind and anxiety adding to this though. I have read that lyme disease can cause false positive syphilis test results. Say if it is a tick bite how common is it that lyme disease causes a false positive VDRL Syphilis test result?
Edward W. Hook M.D.
Edward W. Hook M.D.
18 months ago
Straight to your questions.  I think you are worrying far too  much:

1.  No, there is no association of the sorts of environmental or job-related exposures you mention and false positive serological tests for syphilis such as the VDRL.

2.  Lyme disease rarely causes falsely positive VDRL tests but this is uncommon.  I suspect the symptoms you are experiencing are due to your focus on the area rather than anything else.

As I said above, I really do think you are all too focused on this issue.   As per Forum guidelines however, I have now provided three responses,  Thus, as per Forum Guidelines, this thread will now be closed without further responses.  Take care.  Please don't worry.  EWH
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