STI PCR Panel in Bangkok: What Is Actually Tested, and When to Test

Sexual health testing guide — start here · 2026

Multiplex PCR panels test for a dozen or more organisms at once. Knowing which results matter clinically is what stops a panel becoming a source of unnecessary antibiotics.

By MedEx · Updated September 2026 · Approx. 10-minute read

Quick answer

A multiplex STI PCR panel in Bangkok uses real-time PCR to detect the genetic material of several organisms from a single urine sample or swab. The panels sold locally typically cover Chlamydia trachomatis, Neisseria gonorrhoeae, Mycoplasma genitalium, Trichomonas vaginalis, herpes simplex 1 and 2, Treponema pallidum, and a group of organisms that are frequently part of normal genital flora — Ureaplasma species, Mycoplasma hominis, Gardnerella vaginalis and Candida. The clinical value depends entirely on separating those two groups. PCR is highly sensitive but detects genetic material rather than active infection, and it cannot replace blood tests for HIV, syphilis staging or hepatitis.

In this guide

1. What PCR does and does not tell you
2. The distinction that matters most
3. Choosing the right sample
4. When to test after exposure
5. Choosing a panel without over-testing

What PCR does and does not tell you

PCR amplifies a target sequence of organism DNA or RNA until it is detectable. That gives it very high sensitivity — it can find a handful of organisms where older culture methods would report nothing — and it works on non-invasive samples such as first-void urine.

Two limitations follow directly from that sensitivity. First, PCR detects genetic material, not viable organisms, so it can remain positive for a period after successful treatment. This is why a test of cure is timed deliberately rather than done immediately. Second, when a panel includes organisms that live harmlessly in many people, a positive result does not necessarily mean disease.

Panels also cannot substitute for serology. HIV, hepatitis B, hepatitis C and syphilis staging require blood tests, which is why a complete screen combines PCR with bloods — see the MedEx STD and STI testing service for how the panels are structured.

The distinction that matters most

The bottom row is the one that generates unnecessary treatment. International guidance does not recommend screening asymptomatic people for Ureaplasma or M. hominis, because these organisms are carried by a large share of sexually active adults without causing disease. A positive result in someone with no symptoms is usually not an indication for antibiotics.

If your panel returns one of these, the useful next step is a conversation with a clinician about whether it explains your symptoms — not an automatic prescription. Book a doctor consultation to review the report.

Choosing the right sample

The sample site has to match the exposure. A urine sample will not detect a rectal or pharyngeal infection, and this is one of the most common gaps in routine screening.

• First-void urine — the first 20–30 mL of the stream, ideally at least an hour after last passing urine. Standard for urethral infection.
• Vaginal swab — self-collected vaginal swabs perform as well as clinician-collected cervical swabs for chlamydia and gonorrhoea, and are the preferred sample for women.
• Rectal and pharyngeal swabs — needed where there has been receptive anal or oral exposure. A large share of rectal and throat infections are asymptomatic and would be missed by urine testing alone.
• Lesion swab — for herpes, syphilis or chancroid, swabbing the base of an ulcer or the fluid from a blister gives the highest yield, and should be done as early as possible.

Tell the clinician about all exposure sites when booking through MedEx private testing so the correct swabs are collected.

When to test after exposure

Testing too early produces a false reassurance. Each organism has its own detection window, and PCR windows are shorter than antibody windows because they detect the organism rather than your immune response.

As a broad guide, chlamydia and gonorrhoea PCR is generally reliable from around two weeks after exposure, herpes lesion PCR is best taken while a lesion is present and fresh, and syphilis and HIV need blood tests with longer windows. The full breakdown is covered in the STI window periods guide.

If the exposure was within the last 72 hours and HIV risk is a concern, time matters more than testing: HIV post-exposure prophylaxis must be started as soon as possible and within 72 hours. See MedEx PEP and PrEP services or call the 24/7 helpline rather than waiting for a test appointment.

Choosing a panel without over-testing

Bigger is not better. A panel that adds five commensal organisms adds five opportunities for a confusing positive without adding diagnostic value.

A reasonable approach for most people:

1. Asymptomatic screening after a new partner: chlamydia and gonorrhoea PCR from the appropriate sites, plus HIV and syphilis serology. Add hepatitis B and C depending on risk and vaccination status.
2. Symptomatic urethritis or cervicitis: add M. genitalium with macrolide resistance testing, and Trichomonas vaginalis.
3. Genital ulcers: lesion PCR for HSV and syphilis, plus syphilis serology and HIV testing.
4. Vaginal discharge without exposure risk: this is more often bacterial vaginosis or candida than an STI, and is assessed differently.

Compare available panels and individual organism tests through the MedEx lab test catalogue, or ask the team to build a panel around your actual exposure history.

Frequently asked questions

What does an STI PCR panel test for?

Typically chlamydia, gonorrhoea, Mycoplasma genitalium, Trichomonas vaginalis, herpes simplex 1 and 2, and often Ureaplasma species, Mycoplasma hominis, Gardnerella vaginalis and Candida. It does not cover HIV, hepatitis B or C, or syphilis staging, which require blood tests.

Is a positive Ureaplasma or Mycoplasma hominis result an STI?

Usually not. These organisms are carried by a large proportion of sexually active adults without causing disease, and international guidance does not recommend screening asymptomatic people for them. A positive result should be discussed with a clinician rather than treated automatically.

Can a urine sample detect all infections?

No. Urine will not detect rectal or throat infections, many of which are asymptomatic. Where there has been receptive anal or oral exposure, rectal and pharyngeal swabs are needed.

How soon after exposure can PCR detect an infection?

PCR windows are shorter than antibody windows because they detect the organism directly. Chlamydia and gonorrhoea PCR is generally reliable from around two weeks after exposure, while HIV and syphilis need blood tests with longer windows.

Can PCR stay positive after successful treatment?

Yes. PCR detects genetic material rather than viable organisms, so it can remain positive for a period after treatment. This is why a test of cure is timed deliberately rather than repeated immediately.

Do I need a doctor to order the panel?

MedEx offers confidential direct booking for STI panels, with a doctor consultation available for interpreting results, arranging treatment and advising on partner notification.

Sources and further reading

1. MedEx STD and STI testing service
2. CDC Sexually Transmitted Infections Treatment Guidelines
3. BASHH UK national guidelines
4. WHO guidelines for the management of symptomatic sexually transmitted infections

Medical disclaimer: This article is general health information and does not replace medical advice, diagnosis or treatment. Laboratory reference ranges differ between laboratories and results must be interpreted alongside your symptoms, medicines and medical history. Speak with a qualified clinician before starting, stopping or changing any treatment. Service details, inclusions and prices can change — confirm them with MedEx before booking.