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STD Blood Tests: Which Infections Need One

By Richard D. Porter, Patient Advocate Updated

Quick answer

Blood tests are used to find HIV, syphilis, hepatitis B, hepatitis C and herpes antibodies. They are not used for chlamydia or gonorrhea, which are found with urine or swabs. Each infection has its own timing, and a blood test taken too soon after exposure can miss it. If you may have been exposed to HIV in the last 72 hours, go to urgent care or an ER now and ask about PEP before you test.

The test you need

HIV: Antigen/antibody lab testReliable by day 45

Syphilis: Blood testsRetest if negative before day 49

Hepatitis C: Antibody testReliable by day 77

Too earlyMay detect; retest if negativeReliable

Counted from your most recent exposure. CDC gives no single window for chlamydia, gonorrhea, trich or syphilis; the cautious date uses the NHS "up to 7 weeks". Work out your own dates

Test
Blood tests for HIV, syphilis, hepatitis B and C, and herpes antibodies
Sample
Blood drawn from a vein, or a finger-stick for some rapid tests
When
HIV: lab antigen/antibody test 18 to 45 days after exposure, antibody tests 23 to 90 days, NAT 10 to 33 days (CDC). Herpes antibodies: repeat at about 12 weeks if tested early (CDC).
Results
Rapid HIV tests: 30 minutes or less (CDC). Lab tests take longer. STDCheck says its results are ready in 1 to 2 days.

Blood tests answer a specific set of questions. Some infections can only be found this way, while others can’t be found this way at all.

Which STDs are found with a blood test?

Five infections are tested with blood in most settings:

  • HIV. Options include antibody tests, antigen/antibody tests and nucleic acid tests (NAT), per the CDC.
  • Syphilis. The CDC says diagnosis uses two lab serologic tests, because one type alone is insufficient.
  • Hepatitis B. The CDC says your doctor orders blood tests that look for signs of hepatitis B.
  • Hepatitis C. First an antibody test. If it is reactive, an RNA test checks whether the infection is current.
  • Herpes. Type-specific antibody tests look for HSV-1 and HSV-2 antibodies.

Chlamydia, gonorrhea and trichomoniasis are tested with urine or swabs. Our urine test guide covers those.

How soon can a blood test detect HIV?

The CDC gives these windows after exposure, which differ by test type:

  • NAT: 10 to 33 days (blood from a vein)
  • Antigen/antibody lab test: 18 to 45 days (blood from a vein)
  • Rapid antigen/antibody test: 18 to 90 days (finger stick)
  • Antibody tests: 23 to 90 days

If you test negative within these windows, the CDC says to test again after the window period for the test you used. You can use the window-period calculator to see your dates.

How accurate is a herpes blood test?

Less exact than most people expect. The CDC says glycoprotein-based tests detect HSV-2 antibodies with 80% to 98% sensitivity, and some herpes antibody tests give false positives at low index values, so a confirmatory test may be advised. A test taken too soon can also be a false negative.

The CDC doesn’t recommend herpes testing for people without symptoms in most situations. If you do want one, talk through the result with a clinician. See our herpes blood test accuracy guide for more.

Do hepatitis B and C need blood tests?

Yes. The CDC recommends hepatitis B screening at least once for all adults 18 and older and during each pregnancy. It recommends hepatitis C testing at least once in a lifetime for all adults 18 and older and during each pregnancy.

A reactive hepatitis C antibody test may not mean the infection is current. An RNA test shows whether it’s current.

What can’t a blood test tell me?

  • Where an infection is. A positive herpes antibody test doesn’t say which body site is involved.
  • Whether a sore is herpes. A swab of the sore is the more sensitive test, according to the CDC.
  • Anything it doesn’t include. Ask which tests are in the order.

Can I take a blood STD test at home?

Some. The CDC says FDA-approved self-tests exist for HIV and syphilis, and that you can collect your own blood from a finger prick for self-testing. In 2024 the FDA authorized an at-home, over-the-counter syphilis antibody test, with results in about 15 minutes. The FDA says a positive result should be followed by lab testing through a health care provider. The CDC says the same for a positive HIV self-test.

Who should get a blood test even without symptoms?

Many infections cause no symptoms, which is why screening exists. The CDC says everyone aged 13 to 64 should get at least one HIV test, all adults 18 and older should be screened for hepatitis B and C at least once, and pregnant people should be screened early in pregnancy. For syphilis, screening is recommended for people at increased risk, and at least yearly for sexually active men who have sex with men.

How do I get a blood STD test?

You can ask a clinician, visit a lab, or order online. STDCheck, for example, says its 10-test panel uses blood for HIV, herpes and hepatitis, and urine for chlamydia and gonorrhea. Because a blood draw covers several infections with different windows, plan a repeat test if you test early. The test finder can help you pick.

Get care now if

  • You may have been exposed to HIV in the last 72 hours: go to an ER or urgent care now and ask about PEP
  • You have a rash, new sores, a fever or feel unwell after a possible exposure: see a clinician or urgent care
  • You are pregnant: tell your prenatal clinician. The CDC says pregnant people should be screened for syphilis, HIV, hepatitis B and C early in pregnancy.

Call 911 for a medical emergency. Otherwise, an urgent care clinic, sexual health clinic or your doctor can see you.

When to test

  1. Within 72 hours of a possible HIV exposureGo to an emergency room or urgent care now and ask about PEP. The CDC says PEP must be started within 72 hours and is for emergencies only. Test afterward.
  2. After a possible exposure to HIVChoose the test by how many days have passed. A NAT can detect HIV soonest (10 to 33 days). If you test negative, the CDC says to get tested again after the window period for the test you took.
  3. About 12 weeks after a possible herpes exposureThe CDC says false-negative herpes antibody results are more frequent early on, and advises retesting about 12 weeks after the likely exposure if recent infection is suspected.
  4. If you may have been exposed to hepatitis C in the past 6 monthsThe CDC says your doctor should order an RNA test (NAT) instead of the antibody test.

Common questions

Does a standard blood test check for STDs?

Not necessarily. The CDC says herpes blood tests, for example, may or may not be part of the tests your provider gives you. Ask which infections you are and aren't being tested for, and why.

Can a blood test find chlamydia or gonorrhea?

No. The CDC recommends NAATs on urine or swabs for these infections. A blood test is used for HIV, syphilis, hepatitis B and C, and herpes.

Will a herpes blood test show where the infection is?

No. The CDC says HSV-1 serology can't distinguish oral from genital infection. Routine herpes blood screening in people without symptoms isn't recommended.

How long do STD blood test results take?

It depends on the test. The CDC says rapid HIV tests take 30 minutes or less, while NAT and antigen/antibody lab tests can take several days. STDCheck says its results are ready in 1 to 2 days.

Next: Blood tests for HIV, syphilis, hepatitis B and C, and herpes antibodies.

Blood drawn from a vein, or a finger-stick for some rapid tests. HIV: lab antigen/antibody test 18 to 45 days after exposure, antibody tests 23 to 90 days, NAT 10 to 33 days (CDC). Herpes antibodies: repeat at about 12 weeks if tested early (CDC).

Read next

Sources

This guide is general information written by a patient advocate using public health sources. It is not a diagnosis. Only a clinician or a lab test can tell you whether you have an infection. Read how we write and check our guides.