STI self-test in London: what home kits can tell you — and what they can't

STI self-testing has become significantly more accessible in London. You can order a free NHS kit online, buy a private postal test, or pick up a rapid test at some pharmacies. For many people — no symptoms, testing after a new partner, routine annual screening — a home kit is a practical first step.

But home kits are not the same as clinical tests. They have specific limitations: infections they miss, window periods that affect accuracy, and situations where they simply should not be used. This guide explains what a London STI self-test can and cannot reliably tell you — and when a walk-in clinic appointment is the more appropriate choice.

There are three main ways to self-test for STIs in London without attending a clinic:

• Free NHS postal kits. Ordered online through borough sexual health services or platforms such as SH:24. Primarily available to under-25s, though some boroughs extend eligibility. A kit is posted to you; you collect your sample at home and return it by post. Results arrive by text or secure portal, typically within a few days.
• Private postal kits. Available from a range of private providers. These carry no age or eligibility restrictions and often cover a broader panel than NHS kits. You pay for the test, collect your sample at home, and post it to a laboratory. Turnaround is typically 2–5 days from receipt of your sample.
• Pharmacy rapid tests. Over-the-counter HIV self-tests (such as INSTI or BioSure) are stocked at some London pharmacies. These use a finger-prick blood sample and give a result in around 15 minutes. They test for HIV antibodies only — not a full panel, and with a longer window period than a 4th-generation laboratory test.

Each route suits different circumstances. The right choice depends on what you're testing for, when the exposure occurred, and whether you have any symptoms.

One of the most common misunderstandings about home STI testing is assuming a "full" kit covers everything. It rarely does — and the gap between what a kit covers and what a clinical screen covers is clinically significant.

Every STI has a window period — the time between exposure and when a test can reliably detect infection. Testing inside this window can produce a false negative result: the test returns negative, but infection is present and simply not yet detectable.

This is one of the most clinically important things to understand before using a self-test. Testing too early is among the most common reasons home kit results are misleading or acted upon incorrectly.

A negative result obtained within the window period does not confirm you are infection-free. You should retest once the appropriate window has passed. If you are unsure when your exposure occurred, or if you have any symptoms, speak to a clinician before deciding which test to use and when.

Home kits work well in one specific scenario: asymptomatic screening, at the right time after a known exposure, testing the right sites. Outside that scenario, they have meaningful clinical gaps.

• No rectal or throat screening. If you've had anal or oral sex, infections can be present at rectal or pharyngeal sites without appearing in a urine sample or genital swab. Gonorrhoea at the throat is common and frequently asymptomatic — a standard home kit will miss it entirely. At MDC, rectal and throat swabs are available for anyone who needs them.
• No physical examination. Sores, ulcers, discharge, lesions, or genital abnormalities cannot be assessed by a postal kit. Infections including herpes, syphilis, and genital warts are diagnosed partly through examination — something no home test can replicate.
• No doctor review. Results from home kits arrive as positive or negative without clinical interpretation. If your result is positive, you still need confirmatory clinical testing before treatment. If your result is negative but you have symptoms, a negative does not rule out infection.
• Incomplete infection coverage. No standard home kit covers Mycoplasma genitalium, Ureaplasma, HPV, herpes PCR, Bacterial Vaginosis, or Candida — all of which are included in MDC's clinical profiles.
• Sample collection variability. Self-collected samples — particularly self-taken swabs — are more variable than samples collected by a clinician. Incorrect technique can produce inaccurate results without any indication that the sample was inadequate.

None of this makes home testing without value. It makes it important to understand precisely what the result means in your specific situation.

Home STI self-tests are designed for asymptomatic screening — people with no current symptoms checking their status. If you have any of the following, a clinical appointment is the appropriate next step, not a postal kit:

• Unusual vaginal or penile discharge
• Burning or pain when urinating
• Sores, ulcers, or lesions on or around the genitals
• Pelvic pain or pain during sex
• Rectal pain or discharge
• Unexplained itching or irritation
• Persistent sore throat after oral sex
• Bleeding after sex or between periods

A clinician can collect samples from the correct site, perform an examination if indicated, and interpret results in the context of what they can observe and what you describe. A postal kit cannot do any of these things. MDC offers same-day walk-in appointments Monday to Saturday at 73 Baker Street.

A positive result from a home kit is not a confirmed diagnosis. Clinical confirmatory testing is required before any treatment can be prescribed — this is standard practice across both NHS and private clinical settings. A single positive from a self-collected sample needs verification with a laboratory test on a clinically collected sample.

If your home kit returns a positive result:

1. Do not treat the result as a confirmed diagnosis. False positives occur, particularly with self-collected samples.
2. Abstain from sexual contact until you have a confirmed result and, where appropriate, have completed treatment.
3. Book a clinical confirmatory test promptly. Both NHS walk-in sexual health clinics and private clinics including MDC can provide this.
4. Do not purchase antibiotics online without a confirmed clinical diagnosis and a prescription from a registered doctor.

At MDC, same-day confirmatory testing is available. Results return in 24–48 hours with optional doctor review to discuss next steps.

When a home kit isn't the right tool for the situation, MDC offers three clinical sexual health profiles — each covering more ground than any postal kit, with blood tests, urine tests, and PCR swabs collected by a clinician and processed to laboratory standard.

Individual tests are also available — including Herpes PCR or IgG/IgM (£93–£99), HPV mRNA or DNA typing (£99–£130), and Hepatitis A, B, and C profiles — for patients who need to add specific tests to their screen. Rectal and throat swabs are available for anyone who needs them. Westminster residents receive 20% off.