Re: Will one still test 'reactive' to VDRL long after having been treated?

Edgar,

The VDRL is a blood test that detects antibodies in the blood to the
spirochete bacterium "treponema pallidum" which causes syphilis.

Interpreting the VDRL can be a little confusing because there are false 
positive test due to a variety of other condition as well as other spirochete 
infections. The test does not demonstrate the presence of the spirochete 
but only the antibodies against it. Furthermore, the test does not use an 
antigen made from the spirochete but a nonspecific antigen that "usually" 
is reactive with the antibody. Although it is not a specific test, it is good for 
screening large populations for syphilis because it is easy and quick and 
cheap.

In general, if a test is positive then if can be confirmed with another blood 
test called FTA, which uses a treponeme for the antigen. If it is positive 
then the possibility that the person has syphilis is more likely.

In general, the VDRL should revert to normal after treatment. The FTA, 
which is more sensitive, may remain positive for very long times.

A quantitative VDRL in which the results are reported as being reactive 
after serial dilutions of the blood is very informative. If you are infected with
syphilis the VDRL may be nonreactive until you have developed 
antibodies against it. Then the VDRL becomes positive. It becomes 
positive in greated amounts, that is, the bolood is still positive after serial 
dilutions, Positve at 1:1, 1:2, 1:4, 1:8, 1:16, 1:32, 1:64, etc. After treatment 
the titers should fall: positive at 1:64,then1:32, 1:16, 1:8, 1:4, 1:2, then 
negative.

If you have a transiently false positive test it should revert to normal, If you 
have a chronic condition it may remain positive. If you are reinfected it 
should go up with increasingly positive dilutions.

A person who was treated 10 years ago and now has a rective VDRL 
should have a FTA and a quantitative VDRL done. If the titer is only 1:4, 
then it probably does not indicate a persistent infection or a reinfection.

In general, the diagnosis of syphilis, recurrent syphilis, inadequately treated 
syphilis or a false positive test should be made on the complete clinical 
situation and if still confusing a consultation with a doctor specializing in 
infectious diseases may be necessary.

WMR