What is the Difference Between Treponemal and Nontreponemal Test

The key difference between treponemal and nontreponemal test is that treponemal test detects antibodies directed against proteins of Treponema pallidum during infection, while nontreponemal test detects antibodies directed against both lipoidal materials released from host cells early in an infection and lipids from the cell surface of the treponeme itself.

Syphilis is caused by the spirochete bacterium  Treponema pallidum. The common manifestations of this include genital ulcers, skin lesions, meningitis, aortic disease, and neurologic syndromes. Diagnosis of syphilis is made through different tests performed based on the disease stage. Treponemal and nontreponemal tests are two serological tests usually performed in the laboratory to detect Treponema pallidum infection.

CONTENTS

1. Overview and Key Difference
2. What is Treponemal Test
3. What is Nontreponemal Test
4. Similarities – Treponemal and Nontreponemal Test
5. Treponemal vs Nontreponemal Test in Tabular Form
6. Summary – Treponemal vs Nontreponemal Test

What is Treponemal Test?

Treponemal test is a test that detects antibodies directed against proteins of Treponema pallidum during infection. It is a type of diagnostic test. A popular treponemal test for syphilis is the fluorescent treponemal antibody-absorption (FTA-ABS) test. In this test, the absorbed serum of the patient is layered on a microscope slide that contains fixed Treponema pallidum species. If the patient’s serum contains specific antibodies like IgG and IgM antibodies against Treponema pallidum in the slide, the antibodies will coat the treponeme. In the next step of this test, fluorescein isothiocyanate (FITS) labelled antihuman immunoglobulins are added to the microscope slide. Fluorescein isothiocyanate (FITS) labelled antihuman immunoglobulins combine with the patient’s IgG and IgM antibodies that adhere to Treponema pallidum. This results in a visible test reaction when examined by fluorescence microscopy. However, the FTA-ABS test should not be used as a primary screening procedure. The sensitivity of this test is 85% for detecting primary syphilis, 100% for detecting secondary syphilis, and 98% for detecting late syphilis.

Patients can still test positive for treponemal antibodies after completing syphilis treatment. This typically means the treponemal test cannot distinguish between a current and past syphilis infection.

What is Nontreponemal Test?

Nontreponemal test is a test that detects antibodies directed against both lipoidal materials released from host cells early in infection and lipids from the cell surface of the treponeme itself. The nontreponemal test is usually used as an initial screening test. A positive nontreponemal test should be confirmed with another type of test.

Venereal disease research laboratory (VDRL) test is a type of nontreponemal test. It measures antibodies that are often produced within one to two weeks after a patient develops an initial sore. This test can be performed on blood or spinal fluid. Syphilis leads to the production of non-specific antibodies that react to cardiolipin. Cardiolipin is an important component of the inner mitochondrial membrane. Cardiolipin constitutes 20% of the total lipid composition. Moreover, it can be found in animals, plants, and bacteria. Venereal disease research laboratory (VDRL) test detects non-specific antibodies that react to cardiolipin during the initial infection period. Furthermore, the rapid plasma regain (RPR) test is another nontreponemal test that can be used to detect the above non-specific antibodies.

What are the Similarities Between Treponemal and Nontreponemal Test?

• Treponemal and nontreponemal tests are two serological tests usually performed in the laboratory to detect Treponema pallidum infection (syphilis).
• Both tests detect antibodies.
• Nontreponemal test is always followed by a treponemal test.
• Both tests are performed in clinical laboratories by skilled technicians.
• They are usually inexpensive tests.

What is the Difference Between Treponemal and Nontreponemal Test?

Treponemal test detects antibodies directed against proteins of Treponema pallidum during infection, while nontreponemal test detects antibodies directed against both lipoidal materials released from host cells early in infection and lipids from the cell surface of the treponeme itself. Thus, this is the key difference between treponemal and nontreponemal test. Furthermore, treponemal test is a diagnostic test. On the other hand, nontreponemal test is an initial screening test.

The below infographic presents the differences between treponemal and nontreponemal test in tabular form for side by side comparison.

Summary – Treponemal vs Nontreponemal Test

Syphilis is a sexually transmitted disease caused by Treponema pallidum. Diagnosis of syphilis can be made through different serological tests such as treponemal and nontreponemal tests. Treponemal test detects antibodies directed against proteins of Treponema pallidum during infection, while nontreponemal test detects antibodies directed against both lipoidal materials released from host cells early in infection and lipids from the cell surface of the treponeme itself. So, this summarizes the difference between treponemal and nontreponemal test.

Reference:

1. Henao-Martínez, Andrés F, and Steven C Johnson. “Diagnostic Tests for Syphilis: New Tests and New Algorithms.” Neurology. Clinical Practice, U.S. National Library of Medicine, Apr. 2014.
2. “Syphilis Test.” Encyclopædia Britannica, Encyclopædia Britannica, Inc.

Image Courtesy:

1. “Treponema pallidum-Partikelagglutinationstest” By Copacopac – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “VDRL slide 1” By Netha Hussain – Own work (CC BY-SA 3.0) via Commons Wikimedia