How Accurate Are STD Tests?
Table of Contents
- Written by Tommy Gonzales - Updated on August 2, 2021
- Medically reviewed by Dr Andrea Pinto Lopez, M.D.
Modern STD (sexually transmitted disease) tests have become super accurate, 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 and specificity are related but different concepts. According to Cochrane UK, sensitivity is a test’s ability to accurately determine when someone has the condition that is being tested without producing false negatives, while specificity refers to its ability to determine when a patient doesn’t have the condition without producing false positives. Together, these concepts determine a test’s validity and accuracy.
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 during different stages of the diagnostic process.
Sensitive tests are typically used to screen for initial screening, while more specific tests can be used to ultimately confirm the diagnosis.
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.
Despite the fact that different tests have varying degrees of accuracy, most of the diagnostic tests that are currently in use work very well. If we review the accuracy percentages for different modern testing procedures we’ll find that most of them have sensitivity and specificity values that hover around ~90% or higher, including tests used to diagnose STDs.
As the NHS reminds us, self-administered test kits can be used as supportive screening tools, but they should never replace a proper consultation with a healthcare professional.
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 an infection caused by a parasite. It can be completely asymptomatic in many cases, but other people can experience symptoms such as:
- Genital pain, burning, and/or itching
- Pain during intercourse and/or urination
- Yellow-green, frothy, foul smelling vaginal discharge
- Lower abdominal pain
The NAAT technique is considered to be the gold standard for trichomoniasis, since it has the higest sensitivity.
However, other methods such as saline microscopy and microbial culture are also used. These tests offer a lower sensitivity, but they’re also cheaper and more accesible, particularely for remote or underserved populations.
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.
An HPV test is performed very similarly to a Pap smear. During the test, a healthcare provider gently removes a small sample from a woman’s cervix in order to analyze them and identify the presence of HPV.
According to the American Cancer Society, an HPV can actually be performed simultaneously with a Pap smear, which is another diagnostic test that looks for changes in the cells of the cervix that can be precancerous or cancerous.
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.
1. Advantages and Accuracy of Rapid STD Tests - erywellhealth.com
2. Chlamydia Testing - labtestsonline.org
6. Final Evidence Review for Genital Herpes: Screening - uspreventiveservicestaskforce.org
7. VDRL test - mountsinai.org
8. Syphilis Workup - emedicine.medscape.com
10. Human Papillomavirus (HPV) Test - medlineplus.gov
11. Human Papillomavirus (HPV) Test - medlineplus.gov
12. HPV test - mayoclinic.org
13. HIV Basics - cdc.gov
14. False-Positive HIV Test Results - cdc.gov
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