VDRL Serological Test For Syphilis

Syphilis is a very dangerous veneral disease caused by Treponema pallidum. T. pallidum is a spirochaete. However, if taken out from human blood, it looses its viability. Therefore, this pathogen survives only in human population. It is transmitted from diseased to healthy persons through sexual activity. In addition, it also spreads through transplacental route to developing foetus in pregnant woman. In such cases it is called congenital syphilis.

Syphilis can be diagnosed through several serological tests such as agglutination, precipitation, complement fixation, direct fluorescent antibody (DFA) test, etc. The two most commonly used agglutination tests are VDRL (Veneral Disease Research Laboratory) test and RPR (rapid plasma reagin) card test. In both the tests precipitation reaction takes place between the serum, reagin (increased concentration of antibodies in syphilis affected patients) and cardiolipin (a soluble antigen extracted from beaf hearts).

Requirements

  • Flat clear glass slide with several paraffin rings (14 mm diameter)
  • VDRL antigen
  • Buffered saline solution
  • Serological pipette 0.2 ml capacity)
  • Positive control serum (heat inactivated syphilis serum)
  • Negative control serum (heat inactivated non-reactive serum)
  • Microscope

Procedure

  1. Take flat clear glass slide and number the rings from 1 to 5.
  2. Take clear serological pipette (0.2 ml capacity) and transfer 0.05 ml positive control serum into 1-4 paraffin rings.
  3. Take other serological pipette and transfer 0.05 ml non-reactive serum of negative control into 2-5 rings.
  4. Now, add 0.05 ml buffered saline to rings 3, 4 and 5.
  5. To rings 1, 2 and 3, add one drop of VDRL antigen
  6. Soon rotate the slide for 4 minutes on a flat surface by hand or on a rotating machine so as to make a circle 2 inches in diameter.

Results

Immediately after rotation, observe the slide using a microscope under 100X magnification (10X × 10X = 100X). Small or large sized clumps may or may not be observed. Appearance of no clumps is indication of negative test for syphilis. Large sized clumps indicates a strong reactive reaction and small sized clumps a weak reactive reaction of syphilis.

Reference:

Dr. R. C. Dubey – Practical Microbioogy

Gaurav Singh

Editor in Chief Medical Microbiology & RDT Labs - RDT Labs Magazine

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