How Accurate Are STD Tests?
Modern STD (Sexually Transmitted Disease) tests have become very good. However, it is important to note that there is no existing test that is going to be ~100% accurate every single time. This has to do with the both the sensitivity and specificity of the test. Sensitivity refers to how good a test is at identifying an infection, while specificity refers to how good the test is at identifying who doesn’t have an infection. These are the two factors that determine how effective any given STD test is.
Depending on these characteristics, tests can be classified as screening or diagnostic tests, depending on its sensitivity and specificity values (accuracy), and can be used as first or as last tests.
Over time, we’ve seen massive improvement in tests as part of the fight against the spread of STDs. That said, it should be noted that STD tests aren’t infallible, meaning that there is always the possibility of getting a false-positive or false-negative result, this will depend on various external factors, as well if the test is a Blood Test, a Rapid STD Test, or even an online test.
These values are important, as false positives and false negatives can be obtained from the test. A false positive occurs when someone who doesn’t have an STI (Sexually Transmitted Infection) or STD takes a test and receives a positive result. Instead, a false negative occurs when someone who does have an STI or STD takes a test and receives a negative result.
Besides not every test offers the same reliability or accuracy, the truth is that most tests work very well. In fact, when checking different testing procedures for reliability and accuracy, we’ll find that most offer sensitivity and specificity values around ~90% or higher, especially those used for diagnostic.
Is important to understand as well that, generally, traditional in-lab tests and home-to-lab tests will be more accurate than online-only tests and that the lest type of tests are just a supportive “screening” tools which can be used at first, but no conclusions should arise from them.
How accurate are the tests?
Chlamydia and Gonorrhea
The accuracy of a chlamydia test depends on the kind of test used and the type of sample that’s collected. In the case of chlamydia and gonorrhea, these STDs are tested by using a Nucleic Acid Amplification Test (NAAT) which amplifies the genetic material associated with the bacteria or virus and allows the doctor to identify it. This test has been evidenced to be very accurate and is the gold standard (top choice) for the diagnostic of chlamydia, being ~95% accurate in picking up chlamydia. As said, no test is ~100% accurate.
Trichomoniasis is caused by an infection with a parasite that can infect you without presenting minimal or no symptoms in most cases. Trichomoniasis is tested with the NAAT technique, which is considered highly sensitive and accurate for this disease.
The herpes simplex virus or HSV, is an infection that causes herpes. When sores are present, polymerase chain reaction (or PCR) is considered the test of choice for diagnosing HSV infections, this type of test can detect the presence of the virus in over ~80% to ~90% of the cases. Another preferred option is Cell Culture, this test uses discharges from a sore in order to create a culture or perform a blood test for the antibodies associated with the virus.
Syphilis is usually checked with a blood test to screen for an infection with the bacterium Treponema pallidum, which causes syphilis. This test is called the Venereal Disease Research Laboratory Test (VDRL) test. This test is more accurate (sensitive) during middle stages, reaching almost ~100% values, however, values between 78-86% are estimated for detecting primary syphilis.
Human Papilloma Virus (HPV) is the most common sexually transmitted disease, with millions infected just in the U.S. HPV infections can be classified primarily between two groups, high risk and low risk. The HPV test is only available for women, and consists on a screening test for cervical cancer, instead, detects the presence of HPV, the virus that causes cervical cancer in the system. It is important to note that, certain types of HPV (including type 16 and 18) do increase cervical cancer risk.
HIV is mainly tested with 3 types of blood/saliva tests, including nucleic acid tests (NATs), antibody tests and antigen tests. Generally, HIV are very specific tests with ~99.6% values, this means that most of the people who obtain a negative result won’t have HIV (false-positive HIV test results).
Finally is important to note that, the only 100% guaranteed methods of preventing any STD or STI are either not having any kind of sexual contact or having it inside a monogamous relationship with a non-infected person. In case you are outside one of these two groups, please consider you are at risk of developing an STD or STI, in this case, if you experience any symptoms, a visit to your doctor and receiving an STD test can be the first steps to take.
Written by Tommy Gonzales on March 4, 2020
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