What are the tests for each STD and how do they work?

Hepatitis B Surface Antigen with Confirmation by Neutralization
HIV-1 Antibody Screen With Reflex to Western Blot Confirmation
Syphilis - RPR (Diagnosis) with Reflex to Titer and Confirmatory Testing
Herpes Simplex Virus 1 and 2 IgG, Type Specific Antibody (HerpeSelect®)
Hepatitis C Antibody
Chlamydia trachomatis by Amplified Detection (APTIMA®)
Neisseria gonorrhoeae by Amplified Detection (APTIMA®)

Doesn't every STD testing company use the same tests?

No. They don't. And there are important differences.

While just about every expert in public health or private medicine agrees on which seven STDs pose a threat and should be regularly screened for, there is quite a bit of debate on which tests should be used to screen for these seven STDs.

Even before tSTD's first year (2004), we constructed our first "comprehensive STD test panel". And when spoke with the lab companies and the infectious disease experts and doctors, were surprised to see how many different tests there were for each STD. For example, there are over a dozen tests for HSV-2 (genital herpes) at each laboratory we use.

We put a lot of care into selecting the tests we run. Not just to make sure that we minimize the possibility of a false positive, but also to make absolutely sure that reflex testing is automatically ordered and run to eliminate any delay in reporting a final result to you. This is not necessarily the cheapest way to order testing, but it is the best way to make sure that you can rely on your results report. And get you final results as quickly as possible.

We want to make sure you understand exactly what the tests you order do and how they work. In some cases, each lab does things a little differently. But we have 8 years of experience running and reporting on STDs from the major labs and we’ve learned a lot about which ones work best.

Aren't all the tests "FDA-Approved"?

Yes. Virtually all of the major lab tests are approved by the FDA. However, FDA approval does not mean it is the right test for you or your situation. And some tests, like the PCR test for HIV, are FDA approved for some applications, but not for others

The FDA, like the laboratories themselves, rely on the ordering physician (in this case, that means the testing company such as tSTD) to make sure that they are ordering the right test for the right situation. At tSTD, we have nine years of experience working with both laboratories on full STD panels and we know these tests well.

Hepatitis B Surface Antigen with Confirmation by Neutralization

Methodology: Enzyme immunoassay (EIA)

Hepatitis B surface antigen is the earliest indicator of the presence of acute infection. Also indicative of chronic infection. Test is useful in the differential diagnosis of hepatitis. Hepatitis B virus (HBV) is a DNA virus with a protein coat, the surface antigen (HBsAg) and a nucleic acid core, the core antigen (HBcAg). There are eight different serotypes. Early in infection, HBsAg, HBV DNA, and DNA polymerase can all be detected in serum.

Surface antigen usually appears in the serum after an incubation period of 1 to 6 months following exposure and peaks shortly after onset of symptoms. It typically disappears within 1 to 3 months. HBsAg presence does not reflect the level of active virus, nor does it differentiate between acute and chronic infection or between mild and severe disease. False-positive results are uncommon, but when they occur they are generally due to technical limitations of the test. In low-risk populations, the HBsAg confirmation test can help verify a repeatedly reactive result as a true positive.

If this antigen is detected, a person has HBV infection. A person who has HBsAg in his or her blood can pass HBV to others. A person who has HBsAg in his or her blood for 6 months or longer has chronic HBV infection.

Limitations: Patients who are negative for HBsAg may still have acute type B viral hepatitis. There is sometimes a "core window" stage when HBsAg has become negative and the patient has not yet developed the antibody (anti-HBs). On such occasions, both tests for anti-HBc are usually positive and anti-HBc, IgM is the only specific marker for the diagnosis of acute infection with hepatitis B. In cases with strong clinical suspicion of viral hepatitis, serologic testing should not be limited to detecting HBsAg, but should include a battery of tests to evaluate different stages of acute and convalescent hepatitis.

HBsAg can be detected 1-7 weeks before liver enzyme elevation or the appearance of clinical symptoms. Three weeks after the onset of acute hepatitis about 50% of the patients will still be positive for HBsAg, while at 17 weeks only 10% are positive. The best available markers for infectivity are HBsAg and HBeAg. The presence of anti-HBs is frequently associated with noninfectivity. The chronic carrier state is indicated by the persistence of HBsAg and/or HBeAg over long periods (6 months to years) without seroconversion to the corresponding antibodies. Such a condition has the potential to lead to serious liver damage, but may be an isolated asymptomatic serologic phenomenon.

HIV-1 Antibody Screen With Reflex to Western Blot Confirmation

Methodology: Enzyme Immunoassay (EIA)

It can take up to 6 months from the time you become infected with HIV for the antibodies to be detected in your blood. This is commonly called the "window period," or seroconversion period. During the window period, you are contagious and can spread the virus to others. If you think you have been exposed to HIV but you test negative for it, you should be tested again within 6 months after your last suspected exposure to HIV.

If screen is positive, confirmation by Western Blot will be performed. The etiological agent of acquired immunodeficiency syndrome (AIDS) has been recognized as a retrovirus; human immunodeficiency virus (HIV-1). The virus is believed to be transmitted by sexual contact, blood transfusion, feto-maternal transmission, breast feeding and intravenous drug abuse. The presence of circulating antibodies to the virus indicates prior exposure of the individual to viral antigen(s). The presence of antibody to HIV is not in itself diagnostic of AIDS. Likewise, a non-reactive test result does not exclude the possibility of exposure to or infection with HIV.

Detection of HIV-1 antibodies is the most common and efficient method of determining whether an individual has been infected with the virus. Currently available enzyme immunoassays (EIAs) have analytical sensitivities and specificities that exceed 99% and 98%, respectively. Because of the possibility of false-positive results and their implications, it is important to repeat reactive EIA results and to confirm these results with the Western blot assay. False-negative results can occur when the tests are performed before seroconversion, when the patient is immunosuppressed, and rarely late in the course of AIDS. Western blotting or immunoblotting is used to confirm the presence of antibodies to HIV-1 and/or HIV-2 in a sample that is repeatedly reactive by EIA. It also identifies the antibodies directed against specific HIV-1 and/or HIV-2 proteins. Western blotting is more complex, time-consuming, subjective, expensive, and specific than EIA, and has a lower positive predictive value when performed alone. The positive predictive value of Western blotting performed sequentially with EIA exceeds 99% with samples from low- or high-risk populations.

The Western blot is interpreted as positive, indeterminate, or negative on the basis of the banding pattern (number and type of bands) on the assay strip. The Western blot usually is considered positive if it exhibits antibody reactivity with at least 2 of the p24 (gag region core protein), gp41, or gp120/160 (env region envelope glycoproteins) bands. Indeterminate results may be resolved by DNA PCR or by follow-up testing in 3 to 6 months.

Syphilis - RPR (Diagnosis) with Reflex to Titer and Confirmatory Testing

RPR Methodology: Agglutination; FTA-ABS Methodology: Immunofluorescent Assay (IFA)

The RPR is a screening test for syphilis. False positive results may occur due to systemic lupus erythematosus, malaria, mononucleosis, infectious hepatitis, leprosy,brucellosis, atypical pneumonia, typhus, yaws, pinta, or pregnancy. Positive results will be confirmed with the more specific FTA-ABS. Rapid plasma reagin (RPR) test. The RPR test also detects reagin and is commonly used as a screening test. The RPR test is done on a sample of blood. It is not done on spinal fluid.

A reactive FTA-ABS test confirms the presence of treponemal antibodies but does not indicate the stage or presence of active infection. The FTA-ABS does not distinguish between syphilis and other treponemal infections. Once the FTA-ABS becomes positive, it remains so for long periods, regardless of therapy. False positive reactions have been associated with diseases with increased or abnormal globulins, patients with lupus erythromatosus, positive Anti-Nuclear Antibodies (ANA) and during pregnancy.

Fluorescent treponemal antibody absorption (FTA-ABS) test. The FTA-ABS test is more difficult to do and is not used as a screening test. It may be used to confirm a syphilis infection after a positive screening test. This test detects antibodies to the bacteria that cause syphilis and can be used to detect syphilis in all stages (except for the first 3 to 4 weeks). The test can be done on a sample of blood or spinal fluid. Positive antibody results may be due to current or previous B burgdorferi infection as well as other spirochete-caused diseases such as syphilis, yaws, pinta, leptospirosis, and relapsing fever. Syphilis and Lyme disease may be differentiated by VDRL and RPR tests, both of which are negative in Lyme disease and positive in syphilis. Patients with autoimmune disorders (e.g., lupus erythematosus and rheumatoid arthritis), mononucleosis, rickettsia, Ehrlichia and bacterial infections (eg, Helicobacter pylori) may also have a positive antibody test. A positive IgM result, in conjunction with a negative IgG result, is presumptive evidence of early infection, unless obtained on a specimen collected more than one month following onset. A positive IgM result on a specimen collected more than one month following onset is likely to be a false positive when the IgG result is negative. A positive IgG result with a positive or negative IgM result is presumptive evidence of late infection.

Herpes Simplex Virus 1 and 2 IgG, Type Specific Antibody (HerpeSelect®)

Herpes Simplex Type 1, Herpes Simplex Type 2

Methodology: Immunoassay

Herpes Simplex Virus (HSV) is responsible for several clinically significant human viral diseases, with severity ranging from inapparent to fatal. Clinical manifestations include genital tract infections, neonatal herpes, meningoencephalitis, keratoconjunctivitis, and gingivostomatitis. There are two HSV serotypes that are closely related anti-genically. HSV type 2 is more commonly associated with genital tract and neonatal infections, while HSV type 1 is more commonly associated with infections of non-genital sites. Specific typing is not usually required for diagnosis or treatment. The mean time to seroconversion using the type specific assay is 25 days.

We use the Focus Technologies’ HerpeSelect® 1 and 2 ELISA IgG tests for qualitatively detecting the presence or absence of human IgG class antibodies to HSV-1 and HSV-2 in human sera. The Focus Technologies’ HerpeSelect® 2 IgG test is indicated for testing sexually active adults or expectant mothers for aiding in the presumptive diagnosis of HSV infection. The performance of this assay has not been established for use in a pediatric population, for neonatal screening, or for testing of immunocompromised patients.

Hepatitis C Antibody

Methodology: Immunoassay

Indications: The EIA test is the initial test to determine if an individual has antibodies to HCV Limitations: A negative result may be due to specimen collection.during the seroconversion window period. A negative result may be observed in individuals who are immunosuppressed. A positive result does not differentiate current active from past infection.

Clinical Significance: Hepatitis C Virus (HCV) is a major cause of hepatitis.

Approximately 1% of blood donors are seropositive for anti-HCV. The clinical symptoms of an HCV infection are variable. The presence of HCV establishes a chronic infection in 50 to 80% of cases. The "window" between infection and seroreactivity is highly variable; up to 12 months.

Normal: The blood sample does not contain HCV antibodies. This doesn't always mean you don't have hepatitis C. HCV antibodies can take from several weeks to months to develop. People who have weakened immune systems, such as those who have HIV, end-stage kidney disease, or have had an organ transplant, may not be able to produce HCV antibodies even though they are infected. If your doctor still suspects that you have hepatitis C virus infection even though the antibody test is negative, you will need to take the test again in a few weeks. More than 90% of people develop HCV antibodies within 3 months of becoming infected with the virus. If the test has not already been done, the doctor probably will use an HCV RNA test to look for active infection.

Abnormal: The blood sample contains HCV antibodies. The test cannot distinguish between an active infection, a cured infection, or a past infection with HCV. Your doctor probably will do another test to confirm that you have hepatitis C.

What To Think About: False-positive test results are possible and may be more likely in a person who does not have risk factors for HCV infection. If your test result is positive but you don't have any of the typical risk factors for hepatitis C, your health professional probably will do another blood test to confirm the result. Because your health professional will not be able to tell whether you are capable of spreading HCV to others based on a positive antibody test, you need to take precautions against spreading the virus as long as your blood tests remain positive for antibodies.

Chlamydia trachomatis by Amplified Detection (APTIMA®)

Methodology: Target Amplification Nucleic Acid Probe

The GEN-PROBE APTIMA Combo 2 Assay utilizes the technology of transcription mediated amplification (TMA) to amplify C. trachomatis and N. gonorrhoeae ribosomal RNA (rRNA) for the qualitative detection of these organisms. Clinical specimens are transported in solutions that release and preserve rRNA. DNA-coated magnetic beads are used to purify and concentrate rRNA, removing substances that are potentially inhibitory to amplification (TMA). Amplicon products are detected by hybridization to unique DNA probes labeled with different acridinium esters that specifically target CT and GC nucleic acid sequences in a process call dual kinetic assay (DKA). The presence of multiple copies of target rRNA in each NT and GC organism greatly enhances the sensitivity of the assay. Culture is recommended as the standard for Chlamydia trachomatis detection in suspected sexual abuse and for suspected failure of therapy.

There is a high frequency of co-infection with NG and CT (~40 percent); therefore, sensitive and specific assays with the capability of detecting both CT and GC are especially effective tools for reducing the burden of these STDs. The GEN-PROBE APTIMA Combo 2 Assay is FDA approved for the detection of C. trachomatis and N. gonorrhoeae in endocervical and male urethral specimens and in female and male urine specimens. Clinical trials have documented a greater than 94 percent sensitivity, and this rises to greater than 97 percent for approved specimen types.

Clinical Significance: Chlamydia trachomatis (CT) and Neisseria gonorrhoeae (NG) are two of the most common sexually transmitted diseases (STD) in the United States and worldwide. Each may cause asymptomatic infection, compounding the problem of diagnosis and contributing to the spread of disease. The application of sensitive and specific screening methods for the diagnosis of CT and GC is an important tool for controlling the spread of these organisms and reducing the serious complications of untreated disease.

Nucleic acid amplification tests (NAAT) have consistently exceeded the sensitivities of non-NAAT methods (direct probe, EIA, culture) in the detection of these organisms. The CDC, therefore, recommends use of a NAAT to screen for genitourinary infections with Chlamydia trachomatis and/or Neisseria gonorrhoeae.

Because approximately 75 percent of women and 50 percent of men are asymptomatic, CT may easily spread within at-risk populations. However, screening programs to identify carriers for treatment have proven effective in reducing the incidence of disease. The CDC has recommended screening for all sexually active females under 20 years of age at least annually, and annual screening of women ages 20 and older with one or more risk factors for chlamydia.

The demonstrated increased sensitivity and excellent specificity of nucleic acid amplification tests (NAAT) for the detection of CT has contributed to the effectiveness of these screening programs and of laboratory diagnosis of CT in general. The ability to use specimen types such as urine for analysis, rather than endocervical or vaginal swabs for women or urethral swabs for men, has also contributed to the patient's acceptance of laboratory testing.

Neisseria gonorrhoeae by Amplified Detection (APTIMA®)

Methodology: Target Amplification Nucleic Acid Probe

The GEN-PROBE APTIMA Combo 2 Assay utilizes the technology of transcription mediated amplification (TMA) to amplify C. trachomatis and N. gonorrhoeae ribosomal RNA (rRNA) for the qualitative detection of these organisms. Clinical specimens are transported in solutions that release and preserve rRNA. DNA-coated magnetic beads are used to purify and concentrate rRNA, removing substances that are potentially inhibitory to amplification (TMA). Amplicon products are detected by hybridization to unique DNA probes labeled with different acridinium esters that specifically target CT and GC nucleic acid sequences in a process call dual kinetic assay (DKA). The presence of multiple copies of target rRNA in each NT and GC organism greatly enhances the sensitivity of the assay. Culture is recommended as the standard for Chlamydia trachomatis detection in suspected sexual abuse and for suspected failure of therapy.

There is a high frequency of co-infection with NG and CT (~40 percent); therefore, sensitive and specific assays with the capability of detecting both CT and GC are especially effective tools for reducing the burden of these STDs. The GEN-PROBE APTIMA Combo 2 Assay is FDA approved for the detection of C. trachomatis and N. gonorrhoeae in endocervical and male urethral specimens and in female and male urine specimens. Clinical trials have documented a greater than 94 percent sensitivity, and this rises to greater than 97 percent for approved specimen types.

Clinical Significance: Chlamydia trachomatis (CT) and Neisseria gonorrhoeae (NG) are two of the most common sexually transmitted diseases (STD) in the United States and worldwide. Each may cause asymptomatic infection, compounding the problem of diagnosis and contributing to the spread of disease. The application of sensitive and specific screening methods for the diagnosis of CT and GC is an important tool for controlling the spread of these organisms and reducing the serious complications of untreated disease.

Nucleic acid amplification tests (NAAT) have consistently exceeded the sensitivities of non-NAAT methods (direct probe, EIA, culture) in the detection of these organisms. The CDC, therefore, recommends use of a NAAT to screen for genitourinary infections with Chlamydia trachomatis and/or Neisseria gonorrhoeae.

Because approximately 75 percent of women and 50 percent of men are asymptomatic, CT may easily spread within at-risk populations. However, screening programs to identify carriers for treatment have proven effective in reducing the incidence of disease. The CDC has recommended screening for all sexually active females under 20 years of age at least annually, and annual screening of women ages 20 and older with one or more risk factors for chlamydia.

The demonstrated increased sensitivity and excellent specificity of nucleic acid amplification tests (NAAT) for the detection of CT has contributed to the effectiveness of these screening programs and of laboratory diagnosis of CT in general. The ability to use specimen types such as urine for analysis, rather than endocervical or vaginal swabs for women or urethral swabs for men, has also contributed to the patient's acceptance of laboratory testing.

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