Syphilis Tests (RDR, VDLR) Flashcards
Reagin
antibody produced by infected patient against cardiolipin, an antigen of the spirochete
RPR
Rapid Plasma Reagin
VDRL
Venereal Disease Research Laboratory
MHA-TP
Microhemagglutination-T. pallidum
TP-PA
T. pallidum-particle agglutination
FTA-ABS
fluorescent treponemal antibody absorption
RPR principle.
Patient serum is mixed with antigen reagent. If reagin antibodies are present, they will flocculate with cardiolipin in the reagent. The charcoal particles co-flocculate with the reagent for visualization.
Purpose of ingredients of RPR reagent:
- choline chloride
- lecithin
- cardiolipin
- charcoal
- choline chloride: inactivates complement
- lecithin: stabilizes reagent
- cardiolipin: acts as antigen
- charcoal: allows macroscopic reading of flocculation
Describe 1st stage of syphilis.
Primary. Chancre nodule appears; painless ulcer; heals spontaneously.
Lasts 1-6 weeks.
25% progress to secondary.
Determine which nontreponemal tests are more sensitive and/or specific during various stages of syphilis.
RPR
- 13-41% NR in primary stage.
- Almost all reactive by secondary stage.
- NR by tertiary stage.
VDRL
- Used for early detection of CNS involvement (secondary stage)
- Highly specific, lacks sensitivity (NR in 30-50% neurosyphilis)
- NR by tertiary stage.
Specimen requirements for RPR and VDRL.
RPR: Serum or EDTA plasma if collected within 24 hours.
VDRL: CSF, centrifuged.
Compare and contrast reagents for RPR and VDRL.
VDRL reagent lacks choline chloride (no complement in CSF) and charcoal (microscopic reading).
5 causes for a biological false positive RPR result.
- SLE
- mononucleosis
- leprosy
- malaria
- other autoimmune disease
Ag-Ab reactions that occur in FTA and MHA tests.
FTA: T. pallidum from rabbit testicles + patient serum. Incubate with anti-IgG conjugate with fluorescence.
MHA: Sheep RBCs coated with T. pallidum antigen + patient serum. Read for agglutination.
Quality control requirements for RPR.
- Room temperature at 19-33° C
- Rotator speed at 100±2 RPMs
- Controls should show expected results.
- Antigen dispensing needle should dispense 60±2 drops/mL.
- New antigen lot numbers tested alongside current lot numbers before being put into use.
Contrast clinical utility of non-treponemal vs treponemal tests.
Non-treponemal tests are screening tests. Prone to false positives. Positives should be confirmed with the treponemal confirmatory tests, which are specific to T. pallidum.
WHO’s protocol for syphilis testing.
Traditional standard testing algorithms include screening with a nontreponemal test such as the RPR; a reactive specimen is then confirmed as a true positive with a treponemal test, such as the FTA-ABS. Confirmatory testing is necessary due to the potential for a false-positive screening test result. However, it is highly unlikely that any one patient will have false positive tests using both reagin and treponemal techniques; therefore, any person with a reactive nontreponemal test and a reactive treponemal test has presumptive syphilis.
Describe 2nd stage of syphilis.
Secondary. Systemic. 6-8 weeks after initial chancre.
Generalized rash, lymphadenopathy, malaise, fever, pharyngitis; CNS involvement may occur.
30% of reported cases still have lesion.
Describe 3rd stage of syphilis.
Latent. Rash resolves spontaneously. Clinical sx absent.
1/3 go on to develop tertiary form.
After 18th week, pregnant mothers transmit tremponeme to fetus.
Describe 4th stage of syphilis.
Tertiary. Gummas form on bones, skin, SQ.
Occurs months or 10-30 years after secondary stage.
CV involvement; CNS involvement (neurosyphilis). Irreversible neuro effects.
Quality control requirements for VDRL.
- Needle precision should be checked for delivery of 100±2 drops antigen per mL.
- Room temperature at 23-29° C.
- Rotator should be checked daily and set to 180±2 RPMs.
- Controls should show expected results.
2 major spirochetal diseases
syphilis
lyme
syphilis incubation
10-90 days
syphilis CV involvement
aorta inflammation and destruction of aortic elastic tissue
sx of neurosyphilis
- meningitis (in first 2 years of infection)
- degeneration of lower spinal cord
- general paresis
- chronic progressive dementia
infant syphilis sx
clear or hemorrhagic rhinitis
rash on mouth, palms, soles of feet
Immune response to syphilis
T cells and macrophages are protective
Antibody formed is not protective
RPR false positive rate
1-2%
may be better than VDRL, but not fully standardized
PCR
5 treponemal tests
- direct fluorescent antibody
- FTA-ABS
- MHA-TP
- TP-PA
- EIA
Nontreponemal tests are more sensitive in ….. cases
congenital and neurosyphilis
Treponemal tests are more sensitive in …. cases
latent and tertiary