Can Routine Blood Tests Detect STDs?

A common assumption is that if your GP has run blood tests and everything came back normal, you have been screened for STIs. In most cases, that is not what happened.

Routine blood tests ordered by GPs (full blood count, liver function, kidney function, cholesterol) do not test for sexually transmitted infections unless specifically requested. STI testing requires dedicated tests, and even then, blood tests only detect some STIs. Others require urine samples or swabs.

Understanding what blood tests can and cannot detect saves you from false reassurance and ensures you get the right tests for the right infections.

"A blood test is the only way to screen for HIV, syphilis, and hepatitis. These infections cannot be detected by swab or urine. If you are having a sexual health check, blood work should always be part of it."

Dr Mohammad Bakhtiar, Sexual Health Physician, GMC 4694470

Which STDs can a blood test detect?

Blood tests can detect HIV, syphilis, hepatitis B, hepatitis C, and herpes simplex virus (HSV-1 and HSV-2). These infections trigger an immune response that produces detectable antibodies or antigens in the blood, making blood-based detection reliable after the appropriate window period.

HIV

HIV testing via blood is the most reliable method. A 4th generation test (antigen/antibody combination) detects both HIV antibodies and the p24 antigen, which appears earlier. This test is conclusive from 45 days post-exposure (BASHH, 2024) and screens positive from 28 days.

For earlier detection, HIV RNA PCR testing can identify the virus from 10 days after exposure. This is available at our clinic for £238.75, with same-day results. Standard 4th generation HIV testing is £75 with 24-hour turnaround.

Read more about HIV test accuracy and early detection.

Syphilis

Syphilis is detected by blood tests that look for treponemal antibodies (IgG/IgM). These become detectable from 3–6 weeks after exposure (BASHH, 2024). Syphilis blood testing costs £85 with results in 24 hours.

Because the initial syphilis sore (chancre) is painless and self-resolving, blood testing is often the only way the infection is discovered. Syphilis rates in England have been rising, making routine screening increasingly relevant.

Hepatitis B

Hepatitis B is detected by testing for the surface antigen (HBsAg), which appears in the blood from 3-6 weeks after infection. A hepatitis B surface antigen test costs £68.13 with results in 24 hours. A full hepatitis B profile, which includes surface antigen, core antibody, and immunity status, is £180.

Hepatitis C

Hepatitis C can be detected by antibody testing (from 4-10 weeks post-exposure) or antigen testing (from 2-3 weeks). The antibody test is £137.50; the early-detection antigen test is £85. Both return results within 24 hours.

Herpes (HSV-1 and HSV-2)

Herpes can be detected by a blood test that looks for type-specific IgG antibodies. However, reliable IgG results require 12-16 weeks after exposure for seroconversion. An IgG antibody profile costs £103.75 with 24-hour turnaround.

If you have active sores, a swab PCR is more useful and does not require waiting for seroconversion. Swab testing costs £120.63, results in 3-5 days.

Which STDs do blood tests miss?

This is the critical gap. The most common bacterial STIs in the UK are not detected by blood tests.

Chlamydia

Chlamydia is the most diagnosed STI in England, and it is not reliably detected by blood. Chlamydia requires a urine sample or swab (vaginal, throat, or rectal) tested by PCR. A chlamydia antibody blood test exists, but it indicates past or present exposure rather than current active infection, making it unsuitable for diagnosis.

If you have only had blood tests, you have not been screened for chlamydia. A urine PCR is £103.75 (combined with gonorrhoea), results in 1-3 days.

Gonorrhoea

Gonorrhoea also requires a urine sample or swab. Blood tests do not detect it. Throat and rectal gonorrhoea are particularly common and require site-specific swabs.

HPV

HPV has no blood test. It is detected by swab (PCR) from the cervix, anus, throat, or genital skin. HPV vaccination is the primary prevention strategy.

Trichomoniasis

Trichomoniasis is detected by urine or swab PCR, not blood tests.

Mycoplasma and ureaplasma

These are detected by urine or swab PCR. Mycoplasma genitalium in particular is increasingly recognised as a cause of urethritis and cervicitis, and is not included in standard blood panels.

Blood test vs comprehensive STI screen

Test method	Detects	Misses
Blood only	HIV, syphilis, hepatitis B, hepatitis C, herpes	Chlamydia, gonorrhoea, HPV, trichomoniasis, mycoplasma, ureaplasma, BV
Urine only	Chlamydia, gonorrhoea (urethral/cervical)	Throat/rectal infections, blood-borne infections
Comprehensive screen (blood + urine + swabs)	All of the above	Nothing significant

A blood-only test misses the most common STIs. A urine-only test misses the blood-borne ones. For complete coverage, you need both.

Our Bronze Screen (£250) combines blood and urine testing for chlamydia, gonorrhoea, syphilis, and HIV. The Gold Screen (£475 men, £490 women) adds hepatitis B and C, herpes, mycoplasma, trichomoniasis, ureaplasma, and Gardnerella for near-complete coverage.

"My GP said my bloods were fine"

This is a phrase we hear regularly. If your GP ordered routine bloods, they almost certainly tested your full blood count, liver function, kidney function, and possibly cholesterol and thyroid. None of these tests screen for STIs.

Even if your GP specifically requested HIV and hepatitis, chlamydia and gonorrhoea are still absent from a blood-only panel. If you want to know your STI status, you need to either ask your GP specifically for comprehensive STI testing (urine sample included) or attend a sexual health clinic.

There is no judgement in getting tested. It is a routine part of looking after your health, no different from checking blood pressure or cholesterol.

How we test

Walk-in STI testing is available seven days a week at our Harley Street clinic. No appointment or GP referral is needed. All samples processed by UKAS-accredited laboratories.

Blood results are typically available within 24 hours. Urine and swab results take 1-3 days. FAST testing returns chlamydia, gonorrhoea, syphilis, and HIV results within 6 hours (FAST Screen Simple: £350).

You do not need to use your real name, and we accept cash payment.

Frequently asked questions

Do routine blood tests check for STDs?

No. Standard blood panels (FBC, liver function, kidney function) do not include STI testing. STIs must be specifically requested, and even then, blood tests only cover some infections. Chlamydia and gonorrhoea require urine or swab samples.

Can a full blood count detect an STD?

No. A full blood count measures red cells, white cells, and platelets. It may show signs of infection (elevated white cells), but it cannot identify which infection is present or confirm an STI.

Which STDs require a blood test?

HIV, syphilis, hepatitis B, hepatitis C, and herpes are best detected by blood tests. All other common STIs require urine or swab samples.

Can I request STD blood tests from my GP?

Yes, GPs can order STI blood tests. However, many GPs do not routinely offer comprehensive STI screening, and asymptomatic patients may face longer waits for appointments. Private walk-in testing is immediate and covers all sample types in one visit.

References

• BASHH (2024). UK National Guidelines for HIV Testing.
• BASHH (2024). UK National Guidelines on the Management of Syphilis.
• NICE CKS (2024). HIV infection and AIDS — Diagnosis.
• NHS (2024). Blood tests — Overview.