Can HIV Be Transmitted Through Blood Transfusion?

HIV can be transmitted through blood transfusion, but in countries with modern screening programs, the risk has been driven extraordinarily low. In the United States during the mid-1990s, the estimated risk was roughly one infectious donation per 450,000 to 660,000 screened units, and advances since then have pushed the odds even further down. The story of how blood transfusion went from a major route of HIV transmission to one of the safest medical procedures in existence is worth understanding, especially because the safety is not uniform worldwide and depends on technologies and policies that vary dramatically from one country to another.

How Transfusion-Transmitted HIV Was Discovered

The connection between blood products and HIV emerged in the earliest years of the epidemic, before the virus even had a name. In the early 1980s, physicians reported cases of Pneumocystis carinii pneumonia in people with hemophilia A who had received clotting factor concentrate and had no other known risk factors. Then, in 1983, a case report described an infant who received multiple transfusions shortly after birth to treat rhesus disease, developed recurrent infections by six months of age, and was later linked to a platelet donor who had AIDS. These cases made it clear that whatever was causing AIDS could travel through the blood supply.¹

The problem was that for several years after those reports, there was no reliable way to test donated blood. It was not until 1985, after the virus responsible for AIDS was identified, that antibody-based screening tests were developed and rolled out for use in blood banks. That year marked a turning point: the combination of HIV antibody screening and high-risk donor deferral policies produced a steep drop in transfusion-transmitted infections.¹

The Window Period Problem

Even after antibody testing became standard, a vulnerability remained. When someone is first infected with HIV, there is a stretch of days to weeks during which they carry the virus and can transmit it, but their immune system has not yet produced detectable antibodies. This is known as the window period, and it was the main reason transfusion-transmitted HIV did not disappear entirely after 1985. A donor who gave blood during this narrow window could pass a standard antibody test and still have infectious blood.

A mid-1990s study of U.S. blood donations estimated that about one in every 360,000 donations came from a person in this window period. On top of that, roughly one in 2.6 million seropositive donations slipped through due to laboratory error. Combined, those two sources of risk meant that for every 450,000 to 660,000 units of screened blood transfused, roughly one case of HIV transmission could be expected.²

A case from Italy illustrates how subtle this problem can be. An HIV-1 RNA-positive donation was identified, yet the donor’s p24 antigen test was still negative ten days later. Full antibody seroconversion did not happen until 41 days after the donation. During that entire interval, standard antibody-only screening would have missed the infection.³

How Nucleic Acid Testing Changed the Equation

The answer to the window period problem came in the form of nucleic acid amplification technology, commonly called NAT. Instead of looking for the body’s immune response to HIV, NAT tests look for the virus’s genetic material directly. Because viral RNA appears in the blood before antibodies do, NAT can detect an infection much earlier, shrinking the window period from several weeks down to roughly a week or less.

Plasma fractionators were the first to adopt NAT in the mid-to-late 1990s, motivated by the disaster of thousands of hemophilia patients infected through contaminated clotting factor. German transfusion centers were early pioneers, running pooled NAT testing for HIV-1, hepatitis C, and hepatitis B on batches of up to 96 donor samples. Commercial automated platforms followed, making the technology accessible to blood banks worldwide.⁴

The addition of NAT to antibody screening created a layered safety system. A donation now has to evade both the antibody test and the genetic test to slip through, and the chances of that happening in a high-income country with well-maintained equipment and trained staff are vanishingly small. Current estimates in the U.S. place the per-unit risk at somewhere around one in one to two million, though the exact figure is debated and depends on modeling assumptions.

Pathogen Reduction as a Third Line of Defense

Testing catches nearly every infected donation, but a separate approach tries to inactivate any viruses that might remain. Pathogen reduction technologies treat blood products with chemicals, UV light, or other methods designed to destroy the genetic material of viruses and bacteria, rendering them unable to replicate.

For plasma-derived products like clotting factor and immunoglobulin, these methods have been remarkably effective. No transmission of HIV, hepatitis C, or hepatitis B through U.S.-licensed plasma derivatives has been documented since 1987.⁵ That is nearly four decades of a clean safety record for an entire category of blood products.

However, the picture is more complicated for whole blood and red blood cell concentrates. Some pathogen reduction systems, such as UVC-based methods, have shown limited effectiveness against HIV specifically, reducing viral load by only about one log (a tenfold reduction). HIV’s reverse transcriptase and genomic structure appear to give it some resistance to certain photochemical treatments.⁶ This means pathogen reduction is a useful additional layer, but it is not a substitute for testing.

Donor Screening and the Shift Toward Individual Risk Assessment

Testing blood is only part of the safety strategy. The other half involves deciding who should be allowed to donate in the first place. For decades, many countries imposed blanket deferrals on men who have sex with men, on the basis that this group faced a higher population-level risk of HIV. These policies were always controversial, balancing the statistical reality of HIV epidemiology against concerns about discrimination.

In recent years, several countries have moved toward individual risk assessment, asking all potential donors about specific recent sexual behaviors rather than categorically excluding people based on sexual orientation. Italy made this shift relatively early, switching from a permanent MSM deferral to individual risk assessment in 2001. A study comparing the periods before and after the policy change found no significant increase in the proportion of HIV-positive donors who were MSM, suggesting the new approach did not compromise safety.⁷

The United States followed more gradually, moving first from a lifetime ban to time-based deferrals and then, in 2023, to an individual risk-based approach. Modeling of the new U.S. policy predicts a relatively minor effect on overall blood safety, with any small increase in risk likely offset by gains in the donor pool.⁸ The shift reflects growing confidence in testing technology: when you can detect the virus itself in donated blood, blanket demographic exclusions become harder to justify on purely scientific grounds.

The Complication of PrEP and PEP

One relatively new wrinkle in blood safety involves people taking HIV prevention medications. Pre-exposure prophylaxis (PrEP) suppresses the virus so effectively that someone taking it could be infected with HIV yet test negative on standard screening, including NAT. The drug keeps viral levels too low for tests to pick up, creating a kind of pharmacological window period that lasts as long as the medication is in the body. Current recommendations defer donors for at least three months after the last dose of oral PrEP, or two years for long-acting injectable forms, to ensure the drug has cleared and any hidden infection would become detectable.⁹

Post-exposure prophylaxis (PEP) raises different issues. PEP involves taking antiretroviral drugs after a potential HIV exposure, typically for 28 days. Among blood donors who reported using PEP, the most common reasons were occupational exposure (such as a needlestick in a healthcare setting) and sexual assault.¹⁰ Blood banks defer these donors as well, because someone who needed PEP may have been exposed to HIV. If that exposure resulted in infection and the antiretrovirals are masking it, the donated blood could be falsely cleared by testing.

The core concern in both cases is the same: antiretroviral drugs can suppress the virus below the detection threshold of current tests. Blood centers rely heavily on donor honesty about medication use, which adds a human element to what is otherwise a largely technological safety system.

What Happens If an Exposure Occurs

If someone does receive a transfusion later found to be from an HIV-positive donor, post-exposure prophylaxis with a combination of antiretroviral drugs is the standard intervention. The regimen typically uses three drugs, and timing matters: PEP is most effective when started as soon as possible after exposure, ideally within hours. Special consideration is needed for pregnant recipients, where drug selection must account for fetal safety.¹¹

Hospitals and blood services also maintain systems called lookback and traceback programs to catch these situations. A lookback program starts when a donor is found to be HIV-positive and works forward to identify every recipient of that donor’s previous donations. A traceback program works in the opposite direction: when a transfusion recipient is diagnosed with HIV and names transfusion as a possible source, investigators work backward to identify the donor responsible. These programs link blood banks to HIV clinics and depend on patient consent and good record-keeping to function.¹²

Blood Safety Is Not the Same Everywhere

Everything described so far reflects the situation in well-resourced countries where antibody screening, NAT, and quality assurance are standard. In many low- and middle-income countries, the reality is different. NAT remains expensive and logistically difficult to implement in settings with unreliable electricity, limited trained staff, and tight budgets. Many developing countries still rely on antibody-only screening, which leaves the full window period unaddressed.¹³

Infrastructure problems compound the testing gap. A study of transfusion safety in Kenya identified inconsistent refrigeration, data entry errors, equipment failure, and the absence of quality assurance programs as factors that contributed to transfusion risk in hospitals.¹⁴ Even the best screening test is only as reliable as the cold chain that preserves the blood, the technician who runs the assay, and the data system that flags a positive result before the unit reaches a patient.

For these countries, the most impactful safety measure may not be a more expensive test but rather building a base of voluntary, repeat, non-paid donors. Repeat donors are tested regularly, so infections are caught early. Paid or replacement donors, who donate under social pressure or financial need, tend to carry higher rates of blood-borne infections and are less likely to disclose risk factors honestly.¹³

The Economics of Shrinking an Already Tiny Risk

One of the more uncomfortable questions in blood safety is how much money is worth spending to prevent infections that are already extremely rare. Adding NAT to existing antibody screening in the United States was estimated to cost around $1.5 million per quality-adjusted life-year gained, well above the thresholds typically considered cost-effective for medical interventions.¹⁵ Society has, in effect, decided that blood transfusion safety warrants spending far more per life saved than almost any other area of medicine. The memory of the contaminated blood scandals of the 1980s and early 1990s, which generated enormous public outrage and legal liability across multiple countries, helps explain why.

In lower-income settings the math looks quite different, but still challenging. A cost-effectiveness analysis of adding NAT in Zimbabwe estimated an incremental cost of about $17,774 per quality-adjusted life-year, which exceeded three times the country’s gross national income per capita.¹⁶ In Ghana, basic HIV antibody screening itself was cost-saving compared to no screening at all, averting significant disease burden for a modest outlay. But moving up to individual-donation NAT only became the clearly superior strategy at willingness-to-pay thresholds above roughly $12,000 per disability-adjusted life-year averted.¹⁷ These numbers reveal a stark disparity: the countries with the highest transfusion-transmission risk are also the ones least able to afford the technologies that would close the gap.

Organ and Tissue Transplants Carry Different Risks

Blood transfusion is not the only way HIV can be transmitted through medical procedures involving human biological material. Organ and tissue transplants carry their own risks, and the two are worth distinguishing because the biology is quite different. A striking case from the early 1990s made this point clearly: a single seronegative donor (whose infection was in the window period) provided organs and tissues to multiple recipients. All four organ recipients and all three recipients of unprocessed fresh-frozen bone became infected with HIV. Yet 34 recipients of other processed tissues from the same donor, including corneas, lyophilized soft tissue, ethanol-treated bone, and gamma-irradiated dura mater, tested negative.¹⁸

The difference comes down to how much living cellular material is involved and whether the tissue has been treated with methods that inactivate viruses. A vascularized organ like a kidney or liver is teeming with immune cells that harbor HIV, making transmission nearly certain if the donor is infected. Processed tissues, on the other hand, go through decontamination steps that can eliminate the virus. This case reshaped tissue banking protocols and reinforced the idea that processing methods matter as much as screening tests.

Rapid Tests and Their Limitations

Outside of blood banking, rapid HIV tests have become a widely used tool in clinical settings and community screening. These tests offer results in minutes rather than days, but they are not interchangeable with the laboratory-based assays used in transfusion medicine. An evaluation of several commercially available rapid tests found that their sensitivity for detecting rarer HIV variants was highly variable and sometimes poor. For HIV-1 group O, an uncommon variant found primarily in West and Central Africa, some rapid tests detected the virus in as few as 20% of known positive samples.¹⁹

This matters for blood safety because travelers and immigrants may carry strains not well detected by the diagnostic tools used in their destination country. Blood banks in high-income countries generally use more sensitive fourth-generation laboratory assays combined with NAT, which mitigates this issue. But the existence of less detectable variants is a reminder that HIV is not a single uniform target, and testing strategies need to account for viral diversity.