Syphilis is a venereal disease caused by the spirochaete organismTreponema palladium. This disease develops 3 stages over several years, separated by asymptomatic stages during which diagnosis can only be made by serological tests. As this organism cannot be cultured on artificial media, the diagnosis of Syphilis depends on the correlation between the clinical data and the serological test results.
Antibodies become detectable at bout 3-4 weeks following exposure, and may remain at detectable levels for long periods after treatment. Two groups of antibodies are formed: non-treponemal antibodies which react with nonspecific antigens (VDRL or RPR test); treponemal antibodies which react with the specific antigens to T. palladium (TPHA test). Antibodies specific to non-treponemal antigens are found in active disease and the levels decrease after successful treatment. Specific antibodies persist long after the infection has been treated. It is necessary to test both groups of antibodies since non-treponemal antibodies may arise for reasons other than Syphilitic infection.
The titre of the antibodies detected by the RPR test is a rather exact reflection of the age of the disease and its response to the treatment.
RPR test is a serologic cardiolipid and non-treponemic test for the quick detection of Syphilis. The reagent consists of a suspension of cardiolipin/lecithin/cholesterol and carbon particles in order to improve the visual reading.
Cardiolipid antigens react with the antibodies (reagin) present in the sample and form macroscopically visible black dumps.
Qualitative test (A semi-quantitative approach is also available, please refer to the insert):
Allow the reagents to reach room temperature (20-25°C).
Dispense 1 drop (50µL) of the sample onto a test circle of a reaction slide.
Spread the sample over the entire area of the test circle using the flat end of the plastic stirrer. Use different stirrers for each sample.
Dispense one free-falling drop (16µL) of the antigen suspension with the dispensing bottle/Needle or a pipette.
Rotate the slide at 100 r.p.m. during 8 minutes on an automatic rotor.
Examine immediately the presence or absence of visible agglutination under a good light.
Note: Do not read after 8 minutes.
Easy-to-read and easy-to-intrepret results
Strong positive: Average and large black aggregates generally widespread on all the surface of the test zone. Weak positive: Fine dispersed black aggregates. Negative result: Homogeneous carbon aggregates in the center of the test zone or a gray suspension on all the surface of the test zone.
The negative control should not present any agglutination after 8 minutes.
The positive control should have a positive result after 8 minutes.
If the controls or known samples of patient do not give the expected results, the test must be considered invalid.
Reagents and material
Cholesterol/lecithin/cardiolipin suspension with carbon particules
Quantity: 1×2 ml
Serum containing antibodies
Quantity: 1×0.5 ml
Serum free of antibodies
Quantity: 1×0.5 ml
Dispensing bottle for the reagent:
Needle for the dispensing bottle:
Storage and stability
When stored at 2-8°C and protected from light, the reagent and the controls are stable until the expiry date stated on the label. Do not freeze any of the reagents.
After opening the kit, store the reaction slides at room temperature.
No prozone effect (Hook) was detected up to 1/128.
RPR test has been evaluated in 1995 by the Syphilis reference center in the UK on 675 samples.Results are the following:
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