Taking medicine to prevent HIV might seem a good reason to feel confident about being able or eligible to give blood, yet people on pre-exposure prophylaxis (PrEP) cannot donate while using it, and must wait for three months after their last dose before doing so. How the medicine can affect those tests is important, writes Jaid Debrah in The Conversation, whose recent research suggests a gap in donor education.
Debrah writes:
Daily pre-exposure prophylaxis is around 99% effective when taken correctly – but if someone acquires HIV while taking the anti-HIV meds, the medicine can make the infection harder to detect. And if an infected donation passed through testing undetected, it could transmit HIV to someone receiving the blood.
Research I carried out with colleagues found drugs used in PrEP in some blood donations in England. These medicines have other uses, so their presence cannot confirm why someone took them. Our findings also cannot establish whether donors understood the restrictions, and we did not demonstrate HIV transmission through donated blood.
But our findings raise a question for blood services: how can they explain the restrictions clearly while supporting people’s use of effective HIV prevention?
Why PrEP can make HIV harder to detect
If someone acquires HIV while taking PrEP, the medicine can limit the virus’ ability to multiply, reducing the amount in their blood. It can also delay or weaken the production of antibodies, proteins made by the immune system in response to infection.
Blood services test donations for signs of HIV. These include genetic material from the virus and antibodies produced by the body. Research examining blood samples from studies of PrEP shows that these medicines can make an infection harder to detect.
Someone may have HIV before the tests can reliably identify it, which is why blood services ask questions about a person’s health and medication as well as testing their blood. Those answers provide information that a test result alone cannot supply.
Under UK blood donation guidelines, people must wait three months after their last PrEP tablet before donating. For long-acting injectable PrEP, the waiting period is two years after the last jab, because this can remain in the body for months afterwards.
How donation rules have changed
Blood donation rules have become more inclusive. In 2021, the NHS introduced individual assessments after a review known as Fair (For the Assessment of Individualised Risk).
Previously, men who had sex with men faced restrictions that applied to them as a group. Under the revised approach, donors are asked the same questions about recent sexual behaviour, regardless of gender. This allows more gay and bisexual men to donate while maintaining safeguards for people receiving blood.
For example, anyone who has had anal sex with a new partner or multiple partners must wait three months after the last such contact before donating. Recent PrEP use remains a separate reason why someone must wait.
Someone taking PrEP might understandably feel reassured by its effectiveness and assume that tests on donated blood provide an additional safeguard. But explaining how the medicine can affect those tests really should be part of explaining the donation rules.
What our research found
We tested blood samples collected in 2023 from 84 male donors in England. Their blood showed evidence of current or past syphilis. Six samples, or 7.1%, contained both medicines used in a common type of PrEP tablet.
The same medicines can also be used to prevent HIV after a possible exposure, or as part of treatment for someone who already has HIV. Finding them does not establish that a donor has HIV.
Our wider analysis found that donations showing evidence of current or past syphilis increased from about four to 10 per 100 000 donations between 2018 and 2024. This does not establish that PrEP or changes to donation rules caused the increase.
Because we tested a particular group of donors, these findings cannot tell us how common PrEP use is among everyone who gives blood. Nor can they tell us whether people knowingly disregarded donation rules or misunderstood them.
Making the guidance easier to understand
The reason for the waiting period should be explained wherever people receive information about PrEP and wherever they check whether they can donate blood. Knowing how a medicine can affect test results may make the restriction easier to understand.
Blood services should also make it straightforward for people to ask questions privately.
The different waiting periods for PrEP tablets and injections make clear guidance especially important. Someone familiar with the three-month wait after taking tablets could otherwise assume that the same rule applies to injections.
People should not stop PrEP simply to become eligible to donate blood. Anyone considering a change should discuss it with their doctor or nurse at a sexual health clinic, as stopping removes its protection against HIV.
PrEP remains a major advance in HIV prevention. Explaining why people taking it need to wait before donating can help protect those receiving blood while supporting people’s use of medicine that protects their own health.
Study details
Pre-exposure prophylaxis use in blood donors in England
Jaid Debrah, Claire Reynolds, Victoria Maddox et al.
Published in Vox Sanguinis on 9 March 2026
Abstract
Background and Objectives
The For the Assessment of Individualised Risk (FAIR) framework, introduced by NHS Blood and Transplant (NHSBT) in 2021, aims to reduce stigma and improve equity in blood donor selection, particularly for gay, bisexual and other men who have sex with men (GBMSM). While pre-exposure prophylaxis (PrEP) is highly effective at preventing sexual transmission of human immunodeficiency virus, its declared use excludes individuals from blood donation. This study examined PrEP use among male blood donors with current or past syphilis in England to evaluate guideline compliance and implications for blood safety.
Materials and Methods
Residual plasma samples from syphilis-positive male blood donors collected in 2023 were tested for PrEP. These data were combined with two previous studies of syphilis-positive donors conducted between July 2018 and June 2024, incorporating demographics and reported PrEP use.
Results
The rate of syphilis-positive blood donations increased from 4.09 to 10.32 per 100,000 donations between 2018 and 2024 (p = 0.048, Mann–Kendall trend test) with a rising proportion of past syphilis cases attributed to GBMSM (18%–37%; p = 0.004, Fisher's test, p = 0.001 Mann–Kendall test); 7.1% of syphilis-positive blood samples from male blood donors tested positive for PrEP in 2023, indicating frequent non-compliance with donation guidelines.
Conclusion
Persistent PrEP use among syphilis-positive donors since 2018 suggests gaps in donor education regarding eligibility. Targeted public health interventions, particularly for younger GBMSM, are needed to strengthen sexual health education, PrEP messaging and awareness of donation criteria. Further research into other infections associated with high-risk sexual behaviour is warranted.
Jaid Debrah – PhD Candidate, Blood Safety & Virology (PrEP/GBMSM), University of Oxford, United Kingdom
Vox Sanguinis article – Pre-exposure prophylaxis use in blood donors in England (Open access)
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