If you’re concerned about possible exposure to an STD, then your next step is to seek an STD test. There are a few different ways to test for STDs. The most common method is to use a urine sample, but many people wonder whether blood tests can also be used.
Will a blood test show STDs? Can all STDs be detected by a blood test? We would like to answer the most frequently asked questions about blood tests for STDs.
Can you find STDs in a blood test?
Some STDs can be found by a blood test. In fact, there are some STDs that can only be found by a blood test. However, there are also others that generally can’t be found on a blood test. For these STDs, a urine test or a swab test (of the vagina or the urethra) is the only way to look for the infection. In addition, for certain STDs, either type of test (urine test or blood test) can be used. Whether a blood test is a good way to check for an STD depends on the specific STD that you’re looking for.
What STD requires a blood test?
There are certain STDs that can only be detected by a blood test. These include:
- HIV (the virus that causes AIDS)
- Hepatitis B
- Hepatitis C
All three of these are viruses that are found in the bloodstream. They can be sexually acquired, or they can enter the bloodstream in other ways, such as through sharing needles. HIV infects certain cells of the immune system, while hepatitis B and C both infect liver cells. Because these viruses are found in other parts of the body rather than infecting the genital or urinary tracts, blood tests are the only way to find these particular STDs.
Can a blood test detect all STDs?
There are also some STDs that cannot be detected by a blood test. These include:
- Gonorrhea
- Chlamydia
- Trichomoniasis
- HPV (human papillomavirus)
The organisms that cause these diseases generally don’t enter the bloodstream. Instead, they stay within the genital and urinary tracts. Because of this, a blood test is not the right type of test for these diseases. For HPV, testing generally uses a swab of the cervix, which is the entrance to the uterus. This swab is known as a Pap smear, and is usually performed as part of your regular gynecologist check. For the other diseases on this list, a urine test is most common, and a vaginal or urethral swab test can also be used.
It is possible to do a blood test for antibodies to these diseases. Antibodies are proteins that are produced by your immune system in response to an infection. However, this type of test would only indicate that you have been exposed at some point in the past, but doesn’t indicate whether you have a current infection. For example, if you have antibodies to the bacteria that cause gonorrhea, this means you have been exposed to gonorrhea at some point, but it doesn’t mean that you currently have gonorrhea. Because of this, the antibody test is not very useful, and this type of test for these STDs is rarely performed.
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What STD can be detected by blood test or urine test?
There are also some STDs that can be detected either way. They can be found by a swab or urine test, or by a blood test. These include:
- Syphilis
- Herpes
For syphilis, if there is a sore or ulcer on the genitals or in the anus or throat, then a swab of this lesion can be performed to look for syphilis. However, with this disease, the sore will heal on its own after a few weeks, but the bacteria still remain in the body and can cause serious long-term damage. If the sore has already healed, then a blood test is the only way to detect syphilis.
The blood test for herpes will only show whether you have been exposed to the virus. It will not show whether you currently have an outbreak, or where the virus is located in your body. In most cases, the virus that causes herpes will enter into nerve cells and remain there for life. It can reactivate from time to time and cause outbreaks. Because of this, if you’ve been exposed to the virus, then it’s likely dormant somewhere in your body, but the blood test for herpes doesn’t show where it is (in the mouth, genitals, or anus), or whether it’s causing a current outbreak. If you currently have blisters or sores that might be a result of a herpes outbreak, then a swab of fluid from the area can be used to look for the herpes virus.
Do normal blood tests show STDs?
When you visit your regular doctor for your annual checkup, you will often get some standard blood tests to screen for common health conditions. In most cases, screening for STDs is not included in these tests. Instead, they are generally looking for issues like high cholesterol, liver problems, thyroid problems, and other common conditions.
If you engage in sexual behavior that could put you at risk for STDs, then your doctor may include testing for certain diseases along with your normal blood tests. Make sure that you’re completely honest with your doctor about the activities that you normally engage in, including how many sexual partners you’ve had recently and whether you always used protection. It’s important that your doctor understands your level of risk, in order to know whether STD screening should be included with your normal blood tests.
Can a blood test detect STDs if you’re asymptomatic?
In many cases, STD testing is used for screening. This means testing a person who is not currently having any symptoms of an STD. It’s very common for most STDs not to cause symptoms in many people who are infected, especially in the early stages.
Many people choose to get screening by both blood and urine tests, in order to look for all of the common STDs. Screening for HIV, hepatitis B and C, syphilis, and herpes can be performed by a blood test, while a urine test can be used to look for diseases like gonorrhea and chlamydia. If you choose to have home STD testing, then only a very small blood sample is needed in order to do the blood test. This can be obtained by a fingerprick.
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Sources
Easterbrook PJ, Roberts T, et al. Diagnosis of viral hepatitis. Curr Opin HIV AIDS 2017 May;12(3):302-314. doi: 10.1097/COH.0000000000000370
Lowhagen GB. Syphilis: test procedures and therapeutic strategies. Semin Dermatol 1990 Jun;9(2):152-9.
Screening Recommendations and Considerations Referenced in Treatment Guidelines and Original Sources. Centers for Disease Control and Prevention (2021). https://www.cdc.gov/std/treatment-guidelines/screening-recommendations.htm. Accessed 27 January 2022.
Sexually Transmitted Diseases (STDs). Mayo Clinic (2021). https://www.mayoclinic.org/diseases-conditions/sexually-transmitted-diseases-stds/diagnosis-treatment/drc-20351246. Accessed 27 January 2022.
Stevens DR, Vrana CJ, et al. A Global Review of HIV Self-testing: Themes and Implications. AIDS Behav 2018 Feb;22(2):497-512. doi: 10.1007/s10461-017-1707-8
Workowski KA, Bachmann LH, et al. Sexually transmitted infections treatment guidelines, 2021. MMWR Recomm Rep. 2021;70(4):1-187. doi:10.15585/mmwr.rr7004a1
