Serology

VDRL (Veneral Disease Research Laboratory)

April 14, 2025 by Olivia R

VDRL (Venereal Disease Research Laboratory) is a blood screening test to detect non-specific antibodies produced by the body in response to syphilis infection (Treponema pallidum)

A. Definition & Function

• Definition
1. A non-treponemal laboratory test that detects antibodies (reagins) against lipids released when syphilis bacteria damage host cells
2. Used as an initial screening test for syphilis


• Clinical uses
1. Screening for syphilis infection (primary, secondary, latent)
2. Monitoring the success of treatment (decreasing antibody titer)
3. Diagnosis of neurosyphilis (with cerebrospinal fluid/CSF samples)

B. Working Principle

• Detection target
1. Reagin Antibody : Not a specific antibody against T. pallidum, but rather an antibody that reacts to lipids (cardiolipin) released when bacteria damage host cells
2. Antigens Used: A mixture of cardiolipin, lecithin, and cholesterol (acts as an artificial antigen)


• Flocculaion reaction
1. Serum samples are mixed with cardiolipin-lecithin-cholesterol antigens
2. If reagin antibodies are present, a clot (flocculation) will form which is visible under a microscope
3. If there are no antibodies: The antigen remains evenly distributed (no flocculation)


• Non-treponemal vs Treponemal
1. VDRL/RPR: Non-treponemal test (screening, can be false positive)
2. FTA-ABS/TPPA: Treponemal test (confirmatory, specific for T. pallidum)

C. Difference between non-treponemal and treponemal

• Definition & detection target



Criteria	Non-Treponemal Test (VDRL/RPR)	Treponemal Test (FTA-ABS/TPHA/TPPA)
Target	Antibodies against lipids (cardiolipins) released when host cells are damaged by T. pallidum	Antibodies are specific to Treponema pallidum bacterial proteins
Examples	VDRL, RPR	FTA-ABS, TPHA, TPPA, CIA (Chemiluminescence) Tests

Analogies:

• Non-treponemal = Detection of "scars" (the body's response to infection)
• Treponemal = Detection of "direct cause" (the bacteria itself)


• Differences in working principles



Aspects	Non-Treponemal	Treponemal
Principle	Flocculation reaction of cardiolipin antigen with reagin antibody	Immunological reaction (agglutination/fluorescence) with treponemal antigen
Method	Manual (microscopic) Automatic (RPR)	ELISA Immunofluorescence (FTA-ABS) Agglutination (TPPA)

Example procedure

• VDRL: Serum + cardiolipin antigen → observe flocculation
• FTA-ABS: Serum + T. pallidum antigen → fluorescence detection


• Clinical Application



Purpose	Non-Treponemal	Treponemal
Initial Screening	✅ (Cheap, fast)	❌ (Usually for confirmation)
Confirmation	❌ (High false positive)	✅ (Specific)
Therapy Monitoring	✅ (Titer drops if successful)	❌ (Antibodies persist for life)
Neurosyphilis	✅ (VDRL in CSF)	✅ (FTA-ABS in CSF)



• Advantages & Disadvantages



Parameters	Non-Treponemal	Treponemal
Advantages	Cheap Fast For therapy monitoring	Specific Low false positive Early stage detection
Disadvantages	High false positive Non-specific	Expensive Persistent antibodies (cannot distinguish active/old infection)

Examples of Non-Treponemal False Positives:

• Pregnancy, HIV, lupus, malaria, vaccination.


• Syphilis diagnostic pathway
1. Initial Screening: Non-treponemal (VDRL/RPR)
2. Reactive Result: Confirmation with treponemal (FTA-ABS/TPPA)
3. Special Cases:
• Neurosyphilis: VDRL in CSF + FTA-ABS CSF
• Infant: IgM treponemal test (to differentiate maternal antibodies)

D. Sample Procedure

• Sample preparation
1. Sample: Serum or CSF (for neurosyphilis)
2. Heat Inactivation: Serum is heated to 56°C for 30 minutes to inactivate interfering components


• Examination Steps
1. VDRL antigen is mixed with phosphate buffer (pH 6.0)
2. Serum is dropped onto a perforated slide
3. Add antigen, then rotate (180 rpm, 4 minutes)
4. Observe under the microscope (100x) for flocculation


• Results
1. Reactive: Flocculation is present (possible syphilis)
2. Non-Reactive: No flocculation


• Interpretation of Results

Result	Meaning	Action
Reactive	Antibody detected (possible syphilis or false positive)	Confirm with FTA-ABS/TPHA
Non-Reactive	No active infection* (or very early/late latent stage)	Further clinical evaluation



• Quantitative results
1. Reported as titers (examples: 1:2, 1:4, 1:8, 1:16)
2. Titer drops 4x after treatment = Therapy is effective

E. Common Weaknesses & Problems

1. False Positive
• Causes: Pregnancy, HIV, lupus, malaria, vaccination
2. False Negative
• Causes: Very early stage (<:3 weeks), prozone effect (excessive antibodies)
3. Solutions
• Confirmation with treponemal test
• Repeat test if false negative is suspected

F. Comparison with RPR

G. FAQ

Q: Can VDRL diagnose syphilis for sure?

A: No, screening only. Reactive results must be confirmed with treponemal test (FTA-ABS)

Q: How long after infection is VDRL positive?

A: Usually 1–2 weeks after chancre appears (primary stage)

Q: Can VDRL be used after treatment?

A: Yes, to monitor titer decline, but not for diagnosis of reinfection

H. Latest technologies

1. Automated RPR/VDRL: Devices such as the AIX-1000 for faster results
2. Point-of-Care Tests: Example: SD Bioline Syphilis 3.0 (results in 15 minutes)

Conclusion

VDRL is a sensitive but nonspecific syphilis screening test. Results should always be confirmed with treponemal testing and correlated with clinical symptoms