VDRL Testing Procedure for Syphilis Diagnosis
The Venereal Disease Research Laboratory (VDRL) test is a nontreponemal test that should be performed in conjunction with treponemal-specific tests for accurate diagnosis of syphilis, as no single test alone is sufficient for definitive diagnosis. 1, 2
VDRL Testing Procedure
- VDRL detects nonspecific antiphospholipid antibodies produced by the host in response to phosphatidylcholine taken up from mammalian tissue by Treponema pallidum 3
- Results should always be reported quantitatively as titers, which correlate with disease activity 3, 2
- A fourfold change in titer (equivalent to two dilutions) indicates a clinically significant difference when monitoring treatment response 3, 2
- For cerebrospinal fluid (CSF) testing, the VDRL-CSF is the standard serologic test for neurosyphilis diagnosis 1
Diagnostic Algorithm
- Initial screening should include both nontreponemal (VDRL or RPR) and treponemal-specific tests (FTA-ABS, TP-PA) 3, 2
- When lesions are present, darkfield examinations and direct fluorescent antibody tests of lesion exudate should be prioritized as definitive diagnostic methods 2
- Sequential serologic tests should be performed using the same testing method (e.g., VDRL or RPR), preferably by the same laboratory 1, 2
VDRL vs. RPR Comparison
- VDRL and RPR are equally valid assays, but their quantitative results cannot be compared directly 1, 4
- RPR titers often are slightly higher than VDRL titers 1, 4
- For neurosyphilis diagnosis, CSF-VDRL is more sensitive than CSF-RPR (71.8% vs. 56.4%) 1, 5
- CSF-VDRL has a specificity of 98.3% for neurosyphilis diagnosis 1, 5
Neurosyphilis Diagnosis
- No single test can diagnose all cases of neurosyphilis 1
- Diagnosis typically requires a combination of:
- Reactive serologic test results
- Abnormal CSF cell count (>5 WBCs/mm³) or protein
- Reactive VDRL-CSF 1
- CSF-VDRL may be nonreactive when neurosyphilis is present 1, 6
- Some experts recommend performing an FTA-ABS test on CSF, which is less specific but more sensitive 1, 7
Sensitivity and Specificity
- VDRL sensitivity varies by stage of syphilis: approximately 88.5% in primary syphilis, 100% in secondary syphilis, 82-100% in latent early syphilis, and 61-75% in latent late syphilis 3
- For neurosyphilis, CSF-VDRL has a sensitivity of 71.8% and specificity of 98.3% 1, 5
- Treponemal tests like TP-PA have higher sensitivity (86%) than VDRL (71%) for primary syphilis diagnosis 8
Important Considerations and Pitfalls
- False-positive VDRL results can occur in various conditions, including HIV infection, hepatitis B, hepatitis C, autoimmune diseases, and pregnancy 3, 4
- HIV-infected patients may have abnormal serologic test results (unusually high, low, or fluctuating titers) 1
- Nontreponemal tests usually become nonreactive after treatment, but some patients develop a "serofast reaction" with persistent low titers 1, 4
- Treponemal tests typically remain reactive for life regardless of treatment or disease activity 1, 2
- Using only one type of test (either nontreponemal or treponemal) can lead to misdiagnosis 2