How to prepare for an STI test: do you need to fast?

4 hours ago

3 min read

You don't need to fast for an STI test: you can have breakfast as usual. What matters is not peeing for at least 1–2 hours beforehand if you are giving a urine sample, avoiding vaginal douches, pessaries or creams the day before, and telling us if you have recently taken antibiotics. You only need to fast if, at the same visit, you are having other blood tests that require it, such as glucose or cholesterol.

Do you need to fast for an STI test?

No. Sexually transmitted infection tests, whether on blood (HIV, hepatitis B and C, syphilis) or on urine or swabs (chlamydia, gonorrhoea, mycoplasma, trichomonas, etc.), are not affected by food. You can eat and drink water as usual.

The exception is if you use the visit for a general blood test: some markers, such as glucose or lipids, usually require 8–12 hours of fasting. If that's your case, ask us beforehand.

If you are giving a urine sample

Many bacterial infections are detected by PCR in urine. For a reliable sample:

Don't pee for at least 1–2 hours before collection.
Collect the first part of the stream, which carries the most material from the urethra (we'll explain this at the lab).
It doesn't need to be your first urine of the morning.
Avoid drinking large amounts of water just before, as it dilutes the sample.

Book a test · No appointment needed at C. del Dos de Maig, 283 (Eixample, Barcelona). Same-day results if the sample is taken before 16:00.

If you are having a genital swab

Avoid vaginal douches, pessaries, creams or lubricants in the 24–48 hours before.
As a rough guide, it is best not to have sex in the previous 24 hours.
If you are on your period, let us know: depending on the test, it may be better to wait until it ends.
Your usual hygiene with water is enough; no special washing is needed.

Antibiotics and other medication

If you have taken antibiotics in the last few weeks, let us know: they can make a bacterial infection give a false negative result. Don't stop any medication prescribed by your doctor in order to get tested; just mention it at your visit.

Choosing the right time

More than preparation, what most affects the result is when you get tested. Each infection has its own window period, the time it takes to become detectable:

Chlamydia and gonorrhoea: as a rough guide, from 1–2 weeks after contact.
HIV: between 2 and 6 weeks depending on the technique, with later confirmation if needed.
Syphilis and hepatitis: may require several more weeks.

If you have symptoms, don't wait: get tested as soon as possible.

What to expect on test day at Sermed

No appointment needed: Monday to Friday from 10:00 to 20:00 and Saturdays from 10:00 to 18:00, at C. del Dos de Maig, 283 (Eixample, Barcelona).
The visit lasts about 20 minutes at most; sample collection takes just a few minutes.
Depending on the test, the sample is blood, urine or a genital swab.
If the sample is taken before 16:00, you get your result the same day, online, through a personal, secure link.
The packs include interpretation of the results by a doctor.

If you're not sure which test to choose or have questions about preparation, message us on WhatsApp (+34 603 993 693).

Frequently asked questions

Can I drink coffee before the test?

Yes, it's fine for STI tests. Just try not to pee in the hour or two before if you will be giving a urine sample.

Can I get tested on my period?

Blood and urine tests generally yes. For a vaginal swab, let us know beforehand and we'll tell you whether it's better to wait.

Do I need to bring anything?

If you have previous related reports or results, it can be useful to bring them. For the test itself you don't need to prepare anything special.

How long does the result take?

The same day if the sample is taken before 16:00.