Microbiology Test

Syphilis, Dark field examination

Dr. Nithin Jayan
Medically Reviewed by Dr. Nithin Jayan, MBBS, DNB
Last Updated on Apr 19, 2014
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Test : Syphilis, Dark field examination

Indications : The test is ordered when a single ulcerous sore, along with other symptoms and medical history, appears in a person and the doctor suspects syphilis. The test is mostly employed to diagnose the disease at its early stage.

There is no preparation that is required prior to the test. Do not wash the affected area on the day of test.

The affected site is cleaned with saline. A sample of serous fluid from the syphilis sore is taken by pressing the slide against the site. When observed through dark field, the spiral shaped bacterium, Triponema palladium which causes syphilis, appears against a black background as bright spiral objects.

This diagnostic method is a cheap and effective way of differentiating syphilis from other conditions. However, it has now been replaced by more efficient and reliable blood tests.

Tell the doctor about any antibiotic that you may be taking or applying as they may affect the test result.

Physiology : Syphilis is a sexually- transmitted disease that is spread by the bacterium Triponema pallidum. The disease is highly contagious and can affect the genital and anal regions, besides lips and mouth. Syphilis can affect both men and women.

The syphilis bacteria are very minute and cannot be viewed through an ordinary microscope but can be observed through a dark-field microscope. In this type of microscopy, light rays are not allowed to pass through the slide directly.

Normal Range : No presence of Treponema species

Interpretation : Normal - Negative

No syphilis bacteria are observed through the dark field microscopy. However a negative result does not indicate absence of syphilis.

Abnormal Positive

If characteristic spirochetes are observed through dark field microscope, it is indicative of the fact that the skin sores are due to syphilis. Triponema palladium

Bacteria are easily identified by their corkscrew shape and typical bending movements.

Once diagnosed, the patient will have to be administered antibiotics right away.

Whether the result is positive or negative a blood test may be carried out to confirm the diagnosis.

Sample : Moist serum from lesions, chancre, condyloma.

Test Method : Dark field microscopy

Related Tests : Automated Reagin Test, RPR, VDRL



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