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It is time to shed light on a diagnostic cornerstone often used in the fight against a globally persistent infection.
Syphilis is a sexually transmitted infection that is caused by the bacterium Treponema pallidum, and it has been a significant public health issue for a long time. Early diagnosis is essential to prevent serious health problems and to ensure effective treatment. The TPHA (Treponema pallidum Hemagglutination Assay) test is one of the most reliable methods for diagnosing syphilis. This instrument is vital for the confirmation of a syphilis infection and also for the determination of the treatment to be used.
The TPHA test for syphilis, or Treponema Pallidum Hemagglutination Assay, is a blood test that detects antibodies generated by the immune system of the body to the bacterium Treponema pallidum, which is the cause of syphilis. Unlike other tests at Mahajan Imaging & Labs that detect the presence of bacteria, TPHA is used to determine whether the bacteria have contacted the body and whether a specific immune response has developed.
The test is treponemal, meaning it detects antibodies that bind to components of the bacterium Treponema pallidum. It recognises the hemagglutination concept: if the patient's serum contains the relevant antibodies, these antibodies will trigger clumping of red blood cells (agglutination), which is then specifically treated (sensitised) with syphilis antigens. A TPHA positive or 'reactive' result is a strong indication of an infection with syphilis, either at present or in the past.
The TPHA test has essential functions in the detection and treatment of syphilis:
1. Confirming Diagnosis: The primary role is to confirm the antibodies specific to Treponema pallidum in a patient's serum. Basically, VDRL (Venereal Disease Research Laboratory) and RPR (Rapid Plasma Reagin) tests, which are non-treponemal, may give false-positive results due to other diseases. As a result, the TPHA test for syphilis should be performed as a follow-up test to verify these initial findings. It allows the physician to be sure of the diagnosis before the start of therapy.
2. Identifying Asymptomatic Condition: Syphilis, an infectious disease, follows the sequence of primary, secondary, latent, and tertiary stages. At the stage of latent or tertiary syphilis, symptoms may not be present or can be very vague; thus, it is hard to make a diagnosis clinically. The TPHA test is instrumental at this time, as it detects antibodies that are highly specific and typically persist for a long time after infection; therefore, it enables diagnosis of latent syphilis that may require treatment to prevent progression to severe tertiary disease.
3. Differentiating True Infection: To differentiate a real case of syphilis infection from a biologic false positive, which can happen with non-treponemal tests, e.g. in autoimmune diseases, certain acute infections or leprosy, the TPHA test for syphilis detects the antibodies that are specific to the causative organism.
4. Helping Decision-Making on the Treatment: The treponemal test confirmation is what will help the doctors to make accurate diagnoses and proper plans for the treatment. This is especially true for latent or tertiary syphilis, where the intervention should be done on time to avoid serious complications in the long run such as those affecting the heart, brain, and other organs.
The TPHA test is a simple lab test which basically involves a blood sample:
Sample Collection: A medical professional will take a small amount of blood from a vein in your arm, most probably, through a venipuncture method. After that, the sample is sent for analysis to a laboratory.
Serum Separation: The laboratory receives the blood sample for centrifugation. This process at Mahajan Imaging & Labs separates the liquid portion of blood serum, which contains antibodies.
Serum Dilution: Multiple wells of a microtitre plate receive different concentrations of serum. This is a measure of antibody concentration (titer) if a quantitative result is requested.
Antigen Sensitisation and Mixing: Some special red cells (usually bird) are covered or "sensitised" with Treponema pallidum antigens. Patient serum at different dilutions is added to these sensitised red blood cells.
Incubation: The mixture is incubated at room temperature for approximately 1 hour. During this period, if antibodies to Treponema pallidum are present in the serum, they will bind to antigens on red blood cells.
Observation (Agglutination): The laboratory technician examines the wells under a microscope for agglutination (red blood cell clumping) traces. Clumping is a positive or 'reactive' result as antibodies have linked the sensitized red blood cells together.
The classification of TPHA test for syphilis results depends on whether there is a visible agglutination and the pattern of such agglutination, which is then compared with the control samples:
A reactive TPHA test indicates that the patient has syphilis, at least once in the past. However, because these treponemal antibodies persist in the body even after treatment, a positive TPHA test cannot distinguish between an active, untreated infection and a previously treated infection. For this reason, it is combined with non-treponemal tests such as RPR or VDRL, whose titers indicate disease activity and treatment response.
While the TPHA test is a particular and reliable treponemal test, it has minor limitations that should be taken into account when diagnosing:
Inability to Differentiate: The test cannot distinguish between a past infection and an active infection, because antibodies can persist in the blood for a lifetime.
Window Period: There is a 'window period' in the very early primary stage of syphilis before the immune system produces enough antibodies for detection. A TPHA test performed too early may yield a false-negative result even if the infection is present.
False Positives: Although the test at Mahajan Imaging & Labs is particular, false-positive results may occur, for example, in individuals with specific conditions such as autoimmune diseases (e.g., lupus), infectious mononucleosis, or infection with non-venereal treponemal diseases (e.g., yaws).
Not for Treatment Monitoring: The TPHA test for syphilis is not a tool for monitoring a patient's treatment progress, as is the case with non-treponemal tests (RPR/VDRL), because the antibody levels are usually detectable for life.
A syphilis identification is usually based on the use of two sets of serological tests that are treponemal (specific) and non-treponemal (non-specific/screening).
It is the two-test approach that constitutes the clinical standard: a positive RPR/VDRL (screening) result is confirmed by a specific treponemal test, such as TPHA. Such a pairing is an effective way to ensure the highest accuracy while facilitating treatment monitoring.
The TPHA test for syphilis is mainly used as a confirmation, follow-up test, but certain groups, however, should undergo syphilis screening first, which may result in a TPHA:
Individuals with Reactive Non-Treponemal Tests (RPR/VDRL): In case a person gets a positive result in a first syphilis screening test, a TPHA is necessary for confirmation.
Individuals with Syphilis Symptoms: Those whose symptoms are compatible with syphilis (e.g., painless sores/chancres, rash, swollen lymph nodes).
High-Risk Groups: Persons with risk factors, among which men who have sex with men (MSM), people with multiple sexual partners, individuals having unprotected sex, and persons diagnosed with other sexually transmitted infections (STIs) or HIV, are the most notable.
Pregnant Women: It is imperative to perform a routine screening during pregnancy to prevent vertical transmission of congenital syphilis that may result in serious complications for the baby.
Partners of Syphilis Patients: The sexual partners of the individuals who have been diagnosed with syphilis.
The TPHA test for syphilis is one of the most specific, and therefore, it constitutes the central element in the worldwide program aimed at the control of this STIs that keeps coming back. As it detects in a very reliable manner the immunological response of the body to the Treponema pallidum bacteria, it is the indispensable second step - the confirmation - after a positive screening test.
Healthcare professionals need to know the tpha test for syphilis, including its method and how to interpret the results. Infected persons testing without delay, especially when it is recommended as a consequence of a positive screen or a risky exposure, is the only way for the first and most efficient route of treatment to be opened, thus avoiding the development of devastating tertiary syphilis.
Would you like to know more about the treatment options available for syphilis once the TPHA test is confirmed at Mahajan Imaging & Labs? Contact us to learn more.
Also Read: How Regular Testing Can Detect Hidden Health Issues Early
