This page is general health information, not medical advice. It cannot tell you whether you have an infection. A clinician can, and the testing options on this site are a good place to start.

If you are in San Antonio and worried about a recent encounter, the first question is usually about timing. A test taken too early can miss an infection that a later test would find.

This guide walks through how to plan your testing. It covers the HIV window period, what the std window period means for other infections, and when a short deadline for PEP applies. It also lists free and low-cost places to test in San Antonio.

A window period is the time between an exposure and the point when a test can reliably detect an infection. A clinician or a test result can tell you about your health. This article cannot.

What You Need Before You Start

A rough date of the exposure. An estimate is fine. Write down the date and the type of contact, such as vaginal, anal or oral sex, or shared needles.
A note of any symptoms and when they began. Many infections cause no symptoms, so a lack of symptoms does not settle anything.
A photo ID, if you plan to use the Metro Health clinic. It requires a current photo ID and does not test anonymously.
A list of any medicines you take, and any earlier test results you have.
Your calendar, so you can book a second visit later.

Step 1: Check Whether You Are Within 72 Hours

Start with the clock. The CDC says post-exposure prophylaxis (PEP) for HIV should begin as soon as possible and no later than 72 hours after a possible exposure. PEP is a course of medicine that a clinician prescribes.

If you are inside that window, contact a clinician first and plan your testing second. Testing is still useful, but it does not need to come before the call.

The Alamo Area Resource Center lists PEP among its services. Its number is (210) 625-7200.
Kind Clinic at 730 Isom Road lists PEP as a service. Its general support line is 833-937-5463, and it does not list a location-specific number.
An emergency department can also be asked about PEP outside clinic hours.

Call ahead and say plainly that you may need PEP. Clinic pages do not publish how quickly each site can prescribe it, so confirm that by phone.

Step 2: Learn the Window Period for Each Test

The CDC publishes clear window periods for HIV, and they differ by test type. The table below uses those CDC figures. The window period counts from the most recent possible exposure.

Infection and test type	CDC window period after exposure
HIV: nucleic acid test (NAT)	About 10 to 33 days
HIV: antigen/antibody test, blood drawn from a vein	About 18 to 45 days
HIV: antigen/antibody test, fingerstick	About 18 to 90 days
HIV: antibody test (rapid or self-test)	About 23 to 90 days
Chlamydia, gonorrhea, syphilis, trichomoniasis, herpes, hepatitis C	The CDC treatment guidelines do not give one universal window. A clinician sets the timing based on the infection, the test and the exposure.

That last row matters. You may see a single number for every infection on other websites. The CDC does not publish one for all of them, so the safest plan is to ask a clinician when a specific test is likely to be informative for you.

The CDC also notes that most people will have detectable HIV by the early end of each range, but the later number is the point at which a result is most dependable. A result within the window period is less certain than one after it.

Step 3: Decide on Testing Now, Later, or Both

Many people ask how soon you can test for STD infections after a single exposure. For HIV, the answer depends on the test. A nucleic acid test has the shortest window in the CDC table, but it is not the usual first-line test at every site. Ask what the clinic uses.

A practical approach is to test twice:

Test now. This gives a baseline. It can find an infection you had before this exposure, and it gets care started if something is found.
Retest later. Schedule a second test after the window period for the test type your clinic uses. For HIV, the CDC range for your test type tells you when a later result is more reliable.

Do not wait for symptoms before you test. The CDC notes that many STIs, including chlamydia, gonorrhea and HIV, often cause no symptoms at first. For more on signs worth noticing, see this guide to STD symptoms, when to test and where in San Antonio.

Step 4: Choose Where to Test in San Antonio

You have several free and low-cost choices. The full local list is on our San Antonio clinic list. For a longer walk-through, see STD testing in San Antonio: where to get tested. These are the options most relevant to timing questions.

Metro Health STI Walk-In Clinic

The San Antonio Metropolitan Health District runs this clinic at 512 E. Highland, Suite 150, San Antonio, TX 78210. The phone number is 210-207-8830. Metro Health lists STI and HIV testing, treatment and counseling.

Cost: Metro Health lists a $15 office visit administrative fee. Other fees vary by service.
Hours: Monday to Thursday, 7:45 a.m. to 4:30 p.m., with the latest check-in at 3 p.m. Friday, 7:45 a.m. to 12:00 p.m., with the latest check-in at 10:30 a.m. Check-in may close early when the clinic is at capacity.
Who it serves: Residents of San Antonio and Bexar County, and people with no other way to get STI services. A photo ID is required.

San Antonio AIDS Foundation

SAAF is at 818 E. Grayson Street, San Antonio, TX 78208, phone (210) 225-4715. It lists rapid HIV, syphilis, gonorrhea and chlamydia testing, and says screening is free with no appointment needed. SAAF says gonorrhea and chlamydia results take 7 to 10 days through the state lab.

SAAF hours are Monday 8:30 to 4:00, Tuesday 12:00 to 8:00, Wednesday and Thursday 8:30 to 4:00, Friday 9:00 to 1:00, and Saturday 11:00 to 3:00. It is closed Sunday. SAAF also lists PrEP and doxy-PEP.

Alamo Area Resource Center

AARC is at 303 N. Frio, San Antonio, TX 78207, phone (210) 625-7200. It lists free testing for HIV, hepatitis C, syphilis, gonorrhea and chlamydia, with rapid fingerstick tests for HIV, syphilis and hepatitis C. Walk-ins are listed Monday to Friday, 8 a.m. to 4:30 p.m., and Wednesday until 8 p.m.

Kind Clinic

Kind Clinic, run by Texas Health Action, is at 730 Isom Road, San Antonio, TX 78216. It lists free walk-in HIV and STI testing, STI treatment, PrEP and PEP. Its published clinic hours are Monday, Tuesday and Friday 9 a.m. to 5 p.m., Wednesday and Thursday 9 a.m. to 8 p.m., and the 2nd and 4th Saturdays 9 a.m. to 2 p.m. The clinic notes that walk-in testing hours differ, so confirm before you go. Kind Clinic says doxy-PEP is available to its own patients only.

Other options

CommuniCare Apollo Wellness Clinic (6511 W Loop 1604 N, Ste. 105; (726) 224-3438) lists STD and HIV testing. It offers a sliding fee discount for self-pay patients with family income under 200% of federal poverty guidelines. Its page does not say whether walk-ins are accepted.
BEAT AIDS (210.212.2266) lists free, confidential HIV and STI testing. Its site does not say which location does the testing, so call first.
Test for Texas, a Texas Department of State Health Services program, offers free mailed at-home kits for HIV, syphilis, gonorrhea and chlamydia to anyone in Texas aged 13 or older. DSHS says results arrive in a secure portal seven business days after the sample reaches the lab.
gettested.cdc.gov is the CDC's locator for testing sites by ZIP code.

Step 5: Go to Your Visit and Ask the Right Questions

Tell the clinician the date of your exposure. That date lets them pick the test and the timing. A few questions are worth asking:

Which test do you use for HIV, and what is its window period?
Which tests are most informative today, and which should wait?
When should I come back for a second test?
Do I need testing at more than one body site, such as the throat or rectum?

Be open about the details. Clinicians hear these questions every day, and the information helps them choose the right tests. Nothing about your question needs an apology.

Step 6: Follow Up on Your Results

Write down when and how results will reach you. Some tests give a result at the visit. Others, such as gonorrhea and chlamydia at SAAF, take days.

If an infection is found, a clinician can discuss treatment. Bacterial infections like chlamydia, gonorrhea and syphilis, and trichomoniasis, are curable with treatment from a clinician. HIV, herpes and HPV are not curable, but they are treatable or manageable with care from a clinician.

The CDC STI Treatment Guidelines (2021) recommend retesting about three months after treatment for chlamydia and gonorrhea, because reinfection is common. A clinician can tell you whether that applies to you.

Texas also requires reporting. According to the Texas DSHS notifiable conditions list for 2026, chlamydia, gonorrhea, syphilis and HIV are reportable conditions. Clinicians and labs make those reports to public health, which is a routine part of care.

Tips and Common Mistakes

Mistake: testing once, too early, and stopping. A test inside the window period may not reflect an infection. Plan a second test.
Mistake: waiting for symptoms. Many infections cause none, as the CDC notes.
Mistake: missing the 72-hour PEP window while waiting for the "right" time to test. Call first if you are within three days.
Mistake: assuming one test covers everything. An HIV test does not check for syphilis or chlamydia. Ask which infections are included.
Tip: use protection and talk with partners while you wait for a later result. A clinician can explain what makes sense in your case.
Tip: ask about expedited partner therapy. The CDC says Texas has no EPT statute, but administrative rules let clinicians prescribe for partners of established patients.
Tip for teens: Texas Family Code Sec. 32.003 lets a minor of any age consent to care for reportable infectious diseases, which covers reportable STIs and HIV. The statute also allows a physician to tell a parent, so do not assume a provider will never do so. Ask about privacy first.

What to Expect From Your Results

A result taken after the full window period for your test is more likely to be accurate than one taken earlier. No test is perfect, and a clinician is the right person to interpret what yours means for you.

A negative result after the window period suggests that the test did not detect that infection. It may be reasonable to talk with a clinician about how often to test going forward.
A negative result inside the window period may not be the final answer. Your clinician may suggest repeating the test.
A positive result is usually followed by a confirmatory test and a conversation about treatment or care options.

For context, the San Antonio region has real numbers behind this advice. Texas DSHS reported 5,983 gonorrhea cases and 500 primary and secondary syphilis cases in Bexar County in 2022. CDC data show 373 new HIV diagnoses in Bexar County in 2024. Regular testing is part of how those numbers come to light and get treated.

Your Next Step

Pick the closest option from the list above, or use gettested.cdc.gov to find another site. If you are inside 72 hours, call a PEP-offering site first. If not, test now and mark a date for your second test.

When to Get Tested After Exposure: STD Window Periods Explained