Rapid Plasma Reagin refers to a type of test that looks for non-specific antibodies

Antibody

An antibody, also known as an immunoglobulin, is a large Y-shaped protein used by the immune system to identify and neutralize foreign objects such as bacteria and viruses. The antibody recognizes a unique part of the foreign target, termed an antigen...

 in the blood of the patient that may indicate that the organism (Treponema pallidum

Treponema pallidum

Treponema pallidum is a species of spirochaete bacterium with subspecies that cause treponemal diseases such as syphilis, bejel, pinta and yaws. The treponemes have a cytoplasmic and outer membrane...

) that causes syphilis

Syphilis

Syphilis is a sexually transmitted infection caused by the spirochete bacterium Treponema pallidum subspecies pallidum. The primary route of transmission is through sexual contact; however, it may also be transmitted from mother to fetus during pregnancy or at birth, resulting in congenital syphilis...

 is present. The term "reagin" means that this test does not look for antibodies against the actual bacterium, but rather for antibodies against substances released by cells when they are damaged by T. pallidum.

In addition to screening for syphilis, an RPR level (also called a "titer

Titer

A titer is a way of expressing concentration. Titer testing employs serial dilution to obtain approximate quantitative information from an analytical procedure that inherently only evaluates as positive or negative. The titer corresponds to the highest dilution factor that still yields a positive...

") can be used to track the progress of the disease over time and its response to therapy.

Accuracy

The RPR test is an effective screening test, as it is very good at detecting people without symptoms who are affected by syphilis. However the test may suggest that people have syphilis who in reality do not (i.e., it may produce false positives). False positives can be seen in viral infections (Epstein-Barr, hepatitis

Hepatitis

Hepatitis is a medical condition defined by the inflammation of the liver and characterized by the presence of inflammatory cells in the tissue of the organ. The name is from the Greek hepar , the root being hepat- , meaning liver, and suffix -itis, meaning "inflammation"...

, varicella, measles

Measles

Measles, also known as rubeola or morbilli, is an infection of the respiratory system caused by a virus, specifically a paramyxovirus of the genus Morbillivirus. Morbilliviruses, like other paramyxoviruses, are enveloped, single-stranded, negative-sense RNA viruses...

), lymphoma

Lymphoma

Lymphoma is a cancer in the lymphatic cells of the immune system. Typically, lymphomas present as a solid tumor of lymphoid cells. Treatment might involve chemotherapy and in some cases radiotherapy and/or bone marrow transplantation, and can be curable depending on the histology, type, and stage...

, tuberculosis

Tuberculosis

Tuberculosis, MTB, or TB is a common, and in many cases lethal, infectious disease caused by various strains of mycobacteria, usually Mycobacterium tuberculosis. Tuberculosis usually attacks the lungs but can also affect other parts of the body...

, malaria

Malaria

Malaria is a mosquito-borne infectious disease of humans and other animals caused by eukaryotic protists of the genus Plasmodium. The disease results from the multiplication of Plasmodium parasites within red blood cells, causing symptoms that typically include fever and headache, in severe cases...

, endocarditis

Endocarditis

Endocarditis is an inflammation of the inner layer of the heart, the endocardium. It usually involves the heart valves . Other structures that may be involved include the interventricular septum, the chordae tendineae, the mural endocardium, or even on intracardiac devices...

, connective tissue disease

Connective tissue disease

A connective tissue disease is any disease that has the connective tissues of the body as a target of pathology. Connective tissue is any type of biological tissue with an extensive extracellular matrix that supports, binds together, and protects organs...

, pregnancy

Pregnancy

Pregnancy refers to the fertilization and development of one or more offspring, known as a fetus or embryo, in a woman's uterus. In a pregnancy, there can be multiple gestations, as in the case of twins or triplets...

, autoimmune diseases, intravenous drug abuse, or contamination. It can also occur naturally in the elderly. As a result, these two screening tests should always be followed up by a more specific treponemal test. Tests based on monoclonal antibodies

Monoclonal antibodies

Monoclonal antibodies are monospecific antibodies that are the same because they are made by identical immune cells that are all clones of a unique parent cell....

 and immunofluorescence

Immunofluorescence

Immunofluorescence is a technique used for light microscopy with a fluorescence microscope and is used primarily on biological samples. This technique uses the specificity of antibodies to their antigen to target fluorescent dyes to specific biomolecule targets within a cell, and therefore allows...

, including Treponema pallidum hemagglutination assay (TPHA) and Fluorescent Treponemal Antibody Absorption (FTA-ABS

FTA-ABS

FTA-Abs is a treponemal test for syphilis. Using antibodies specific for the Treponema pallidum species, such tests are more specific than non-treponemal testing such as VDRL. In addition, FTA-Abs turns positive earlier and remains positive longer than VDRL. Other treponemes, such as T...

) are more specific and more expensive. Unfortunately, false positives can still occur in related treponomal infections such as yaws

Yaws

Yaws is a tropical infection of the skin, bones and joints caused by the spirochete bacterium Treponema pallidum pertenue...

 and pinta

Pinta (disease)

Pinta is a human skin disease endemic to Mexico, Central America, and South America. It is caused by infection with a spirochete, Treponema pallidum carateum, which is morphologically and serologically indistinguishable from the organism that causes syphilis.-Presentation:Pinta is thought to be...

. Tests based on enzyme-linked immunoassays are also used to confirm the results of simpler screening tests for syphilis.

Alternatives

Another test often used to screen for syphilis is the Venereal Disease Research Laboratory VDRL

Venereal Disease Research Laboratory test

The Venereal Disease Research Laboratory test or VDRL is a blood test for syphilis and was developed by the former Venereal Disease Research Laboratory, now the Treponemal Pathogenesis and Immunology Branch, of the United States Public Health Service...

slide test. However, the RPR test is generally preferred due to its ease of use.

Other types of tests are currently being evaluated as possible alternatives to, or as replacements for, the rapid plasma reagin test. One of these alternatives is an immunochromatographic strip test. A study published in February 2006 found that this test outperformed the RPR test in values of sensitivity and specificity, and it does not require a laboratory to process the results.

Fluorescent Treponemal Antibody Absorption Test is the most specific test for syphilis. If this is positive it confirms the diagnosis.