Serologic study of specimens with borderline FTA-ABS test reactivity.

Area of Science:

• Medical Laboratory Science
• Immunology
• Serology

Background:

• The fluorescent treponemal antibody absorption (FTA-ABS) test is a key diagnostic tool for syphilis.
• Inconclusive or borderline results in FTA-ABS testing present challenges in accurate syphilis serodiagnosis.
• Understanding the causes of borderline FTA-ABS reactions is crucial for refining laboratory practices.

Purpose of the Study:

• To analyze sera with borderline reactivity in the FTA-ABS test.
• To determine if additional serological tests can resolve ambiguous FTA-ABS results.
• To investigate potential causes of false-positive or atypical fluorescence in FTA-ABS testing.

Main Methods:

• Reviewed 23,807 sera tested with FTA-ABS, identifying 479 (2%) with borderline results.
• Performed Treponema pallidum microhemagglutination (MHA-TP) tests on borderline FTA-ABS specimens.
• Conducted fluorescent antinuclear antibody (FANA) tests on borderline FTA-ABS specimens to assess for antinuclear antibody interference.

Main Results:

• Only 1% of borderline FTA-ABS sera showed non-specific hemagglutination with MHA-TP.
• 82.5% of borderline FTA-ABS sera yielded negative results with the MHA-TP test.
• 1.5% of borderline FTA-ABS sera were reactive by FANA, indicating antinuclear antibody was not a major cause of inconclusive results.

Conclusions:

• Borderline FTA-ABS results are infrequent and difficult to resolve with MHA-TP or FANA testing.
• Antinuclear antibodies do not appear to be a significant factor contributing to atypical FTA-ABS fluorescence.
• The study highlights the ongoing challenges in interpreting borderline results within syphilis serology.