Syphilis – Part 2 – V.D.R.L (Venereal disease research laboratory test)

Sample

• This is done on the serum of the patient.

Purpose of the test (Indication)

• This is a screening test for syphilis.

Pathophysiology

1. Syphilis is a venereal disease.
2. The causative agent for syphilis is Treponema pallidum, which is a spirochete.
3. The spirochete is 8 to 15 µm in length, gram-negative organisms.

4. Spirochaetes are microaerophilic but this organism cannot be cultured in vitro.
5. This is motile with rotation around its long axis as well as flexion and extension laterally.
6. T.pallidum survives in the patient with syphilis and it has no other habitat.
7. The untreated disease has three stages and these may last for many years.
   1. Primary stage.
   2. Secondary stage.
   3. Tertiary stage.

8. This test will detect antibodies against Treponema Pallidum, and these antibodies appear in 4 to 6 weeks.
9. VDRL is a nontreponemal test that detects reagin and antibodies that act against cardiolipin as an antigen.
10. During primary and tertiary syphilis the test may be falsely negative.
11. Another nontreponemal test is Rapid plasma reagin (RPR).
12. VDRL is a screening test.
    1. VDRL may show the negative result is late syphilis.
13. Other treponemal antibody tests are:
    1. TP-PA ( particle agglutination T.pallidum ).
    2. FTA-ABS ( fluorescent treponemal antibody test.

VDRL test principle

1. This test is performed using a cardiolipin-lecithin cholesterol antigen.
2. Heat-inactivated serum from the patient is used.

3. This test can also be done on the CSF as well.
4. Advantage:
   1. This is inexpensive.
   2. This is reproducible.
5. Disadvantage:
   1. Not 100% specific for syphilis.
   2. Confirm by FTA-ABS or TP-MHA test.
   3. Run positive and negative control

NORMAL

• A negative test means that no antibody to syphilis has been detected.
• This screening test is most likely positive for Secondary and latent syphilis.

Negative VDRL

1. No syphilis.
2. Done when antibodies are still not developed.
3. In the late or inactive phase.
4. The patient has an immune deficiency.
5. Lab error.

False-positive test

1. HIV
2. Lyme disease
3. certain types of pneumonia
4. Malaria
5. Systemic lupus erythematosus.

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