Prep and HIV testing in blood donations: UK rules and new research

Pre-exposure prophylaxis (Prep) for HIV prevention can affect the safety net provided by HIV tests on donated blood. The article outlines why donation rules require a waiting period after Prep, how long the wait is for tablets versus injections, and what that means for donor eligibility and patient safety. It also summarizes a 2023 English donor study and discusses the need for clearer communication about how Prep can influence test results.

• Prep use disqualifies donation during treatment; the waiting period is three months after last tablet dose and two years after injection.
• Prep can limit HIV detectability in blood tests by reducing virus levels or delaying antibody production.
• UK donor guidelines moved to individual risk assessments in 2021, with questions about sexual behavior applied equally regardless of gender; Prep use remains a separate waiting reason for donation.
• In 2023, six of 84 donors had medicines used in Prep present in their blood samples; this does not prove HIV infection but highlights testing complexities.

Overview

The article examines how medicines used for HIV prevention, specifically Prep, interact with the testing and rules surrounding blood donation. It explains why donors who use Prep must wait before giving blood and how the waiting periods differ for tablet versus injectable Prep. The piece also considers the broader policy context and the need to communicate restrictions clearly to potential donors while continuing to protect recipients.

Why Prep can hinder HIV detection

When someone acquires HIV while taking Prep, the medication can limit viral replication in the blood, lowering viral load, and can delay or weaken the production of antibodies. Two main HIV detection approaches used in blood screening are nucleic acid tests (which look for the virus’s genetic material) and antibody tests (which detect immune responses). If Prep suppresses the virus or antibody response, a donation could test negative despite being HIV positive, which is why additional donor screening questions accompany laboratory tests.

Testing in blood donations and limitations

Blood services screen for HIV using both genetic material and antibodies. Research cited in the article notes that Prep medicines can complicate detection, meaning a donor may be HIV-positive but still yield a negative test result at the time of donation. The article emphasizes that donor health and medication history provide information not captured by a test alone, underscoring the value of questions around health and medications as part of the screening process.

Waiting periods and the differences between Prep forms

Under UK guidelines, anyone who has taken Prep tablets must wait three months after the last dose before donating. For Prep given by injection, the waiting period is two years after the last injection. Long-acting injectable Prep can remain in the body for months after stopping, and the waiting periods apply regardless of sexuality. The guidance also notes that other donor conditions must be met.

Changes to how donation guidance is delivered

Donation rules in the UK have become more inclusive, with the Fair process (For the Assessment of Individualised Risk) guiding individualized risk assessments. The revised approach asks donors about recent sexual behavior regardless of gender, enabling more gay and bisexual men to donate while maintaining safeguards for recipients. Prep use remains a separate reason for wait times, which helps ensure safe blood transfusions while supporting HIV prevention strategies.

What the research found

The authors tested blood from 84 male donors in England in 2023. Six samples (7.1%) contained both medicines used in a common Prep tablet. These medicines can also be used for post-exposure prevention or HIV treatment, so their presence does not confirm HIV infection nor do they indicate donor noncompliance with rules. The wider analysis showed that records of current or past syphilis increased from about four to ten per 100,000 donations between 2018 and 2024, but the study does not establish a causal link between Prep use or rule changes and this trend. The researchers caution that the sampled group limits generalizability to the entire donor population and cannot determine whether donors were aware of restrictions or intentionally violated them.

Implications for communication and practice

The article argues for clearer explanations of why waiting periods exist and how Prep can affect test results to improve understanding of donation rules. It also advocates for private, non-judgmental spaces where people can discuss medications and sexual health with healthcare providers. Clear, age- and situation-appropriate guidance is especially important given the different rules for tablets and injections, and the ongoing role Prep plays in HIV prevention.