VDRL (Venereal Disease Research Laboratory) is a serological (blood) test that is mainly used in the investigation of Syphilis. Syphilis is a Veneral ( sexually Transmitted Infection) caused by Treponema pallidum. There Are stages of this disease and each stage presents with different signs and symptoms.
In primary syphilis, the chancre appears when the body is yet to produce antibodies to Treponema pallidum, so blood tests (VDRL) are usually negative/non-reactive at this stage. Laboratory confirmation can be made after collecting material from the ulcer for direct visualization of the bacteria under a microscope. This test is not always necessary, since the genital ulcers of syphilis are well characterized. Your doctor will usually start treatment based only on clinical data like sexual history, whilst waiting a week or two to confirm the laboratory diagnosis.
The diagnosis of secondary syphilis, tertiary, or primary, as in later phases, is done by two serological tests: VDRL and TPHA.However, VDRL is commonly done.
The VDRL test is the simplest and screening used. VDRL usually becomes positive between 4 and 6 weeks after contact with someone with syphilis. So if the test is done one or two days after the appearance of the lesion of syphilis, the VDRL test can give false negative.
It is However not very specific to Syphilis. As the VDRL may be positive in several diseases other than syphilis, such as lupus, liver disease, mononucleosis, leprosy, smallpox, rheumatoid arthritis, etc.
The values of the VDRL after curing fall progressively, becoming negative after some years. VDRL is usually used for disease screening and TPHA is for confirmation.
The TPHA (Treponema pallidum hemagglutination assay) test is more specific and sensitive than the VDRL. The window period is shorter, and may be positive already after a few days after the appearance of the chancre.
The TPHA also has lower rates of false positive than VDRL.
NOTE: When you test Positive for VDRL, make sure you do TPHA to confirm. These are the possible results and interpretations for your education:
1. Positive VDRL and positive TPHA test confirms the diagnosis of syphilis
2. Positive VDRL and negative TPHA indicate that there is other disease, not syphilis
3. Negative VDRL and positive TPHA test indicate very early stage syphilis or healed syphilis or syphilis in the tertiary stage
4. Negative VDRL and negative TPHA dismiss the diagnosis of syphilis (there are rare cases where the test is done too early, there may be false negative on both tests)
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