What is the Difference Between VDRL and RPR

The key difference between VDRL and RPR is that VDRL is a nontreponemal test that needs a microscope to diagnose syphilis, while RPR is a nontreponemal test that does not need a microscope to diagnose syphilis.

Syphilis is a sexually transmitted bacterial infection. It is caused by Treponema pallidum. There are two main tests to detect this bacterium. They are nontreponemal and treponemal tests. Nontreponemal tests detect non-specific treponemal antibodies, while treponemal tests detect specific treponemal antibodies.

CONTENTS

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

What is VDRL (Venereal Disease Research Laboratory)?

Venereal Disease Research Laboratory (VDRL) is a nontreponemal test to detect syphilis infection. This test does not look for the bacterium that causes syphilis. It checks for non-specific antibodies that the body makes in response to antigens produced by cells damaged by the bacterium. Therefore, doctors can diagnose whether patients have syphilis or not by testing for these non-specific antibodies. Doctors perform this test if people have early symptoms such as one small, painless sore, swelling in the lymph nodes near the sores, and skin rash that does not itch.

In a VDRL test, the patient’s serum or cerebrospinal fluid, which contains non-specific antibodies, is placed on a glass slide containing a mixture of cardiolipin (antigens solution). Moreover, the serum is inactivated by heating in order to remove non-specific inhibitors such as complements. This reaction causes flocculation or clumping on the glass slide, which can be detected through a microscope. Furthermore, VDRL is a qualitative test for screening syphilis. The results indicate reactive if clumping occurs or non-reactive if there is no clumping. VDRL test is the only test that can be done using cerebrospinal fluid. However, VDRL is less effective than RPR.

What is RPR (Rapid Plasma Regain)?

Rapid plasma regain (RPR) is a modified version of the VDRL non-treponemal test for syphilis infections. RPR has the same antibody-antigen reaction as VDRL. But RPR contains carbon or delicately divided charcoal particles that allow the visualization of the reaction (flocculation) between specimen (serum containing antibody) and antigen without the aid of a microscope. The results of the RPR test can be seen by the naked eye without a microscope. Moreover, this is the most preferred syphilis test done by many. It is very easy to use and can be readily purchased in a kit form when compared to VDRL.

Furthermore, when performing RPR, the specimen is needed to be heated. In addition to that, cerebrospinal fluid cannot be used in the RPR test as in VDRL.

What are the Similarities Between VDRL and RPR?

• VDRL and RPR are two types of nontreponemal tests to detect syphilis infection.
• Both tests are types of serological tests.
• They detect non-specific treponemal antibodies.
• Both tests use serum as the specimen.
• These tests are normally non-expensive.

What is the Difference Between VDRL and RPR?

VDRL is a nontreponemal test that detects syphilis with the aid of a microscope, while RPR is a nontreponemal test that detects syphilis without the aid of a microscope. Thus, this is the key difference between VDRL and RPR. Furthermore, VDRL is less effective than RPR.

The below infographic presents the differences between VDRL and RPR in tabular form for side-by-side comparison.

Summary – VDRL vs RPR

Syphilis is a sexually transmitted disease that causes skin sores in various parts of the body. The bacterium, Treponema pallidum, causes this disease, and it can be diagnosed through two different tests: nontreponemal and treponemal tests. Nontreponemal tests detect non-specific treponemal antibodies. There are two main types of nontreponemal tests used commonly in laboratories. They are VDRL and RPR. VDRL test needs a microscope to diagnose the infection, while RPR test does not need a microscope to diagnose the infection. So, this is the key difference between VDRL and RPR.

Reference:

1. Holm, Gretchen. “VDRL Test: Purpose, Procedure, and Results.” Healthline, Healthline Media.
2. “RPR Test: Why Is It Used, What to Expect, and Related Tests.” WebMD.

Image Courtesy:

1. “VDRL slide 1” By Netha Hussain – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “Rapid plasma reagin” By Jameswalker yu – Own work (CC BY-SA 3.0) via Commons Wikimedia