Screening blood donors for infection (note)

For educational purposes only. Check the current guidelines. Do not use this note to make clinical decisions.

Author: microregistrar
Updated: 6 November 2026
Scope: UK blood donation screening, with a comparison of tissue and stem-cell donation requirements.

Educational study note for microbiology and FRCPath revision. This is not a clinical guideline, a donor-eligibility tool or a laboratory standard operating procedure. Clinical decisions must follow current JPAC donor-selection guidance, national blood-service procedures and the relevant tissue or transplant standards.

Overview

Infection safety depends on donor selection, assessment of relevant exposures, laboratory screening, appropriate component processing and haemovigilance. A negative screening result does not eliminate infection risk: infection may be too early to detect, and not every potentially transmissible organism is included in routine screening.

The main UK source for laboratory screening requirements is the JPAC Red Book, Chapter 9. Blood, tissue and stem-cell donation requirements are not interchangeable. In particular, hepatitis B core antibody (anti-HBc) has different classifications and release pathways in blood and tissue/cell donation. [web:28]

How to interpret the categories

Mandatory: an absolute requirement before release. The basis may be legislation, regulation or a national policy requirement.
Additional, also called discretionary: performed because of an identifiable donor or recipient risk or a particular regulatory requirement. When indicated, the result forms part of the release criteria; “additional” does not mean unimportant.
Optional: used in particular tissue-donation pathways. For example, donation-sample HIV, HBV and HCV nucleic acid testing may replace 180 days of quarantine and follow-up serology in an applicable pathway. [web:28]

A test can be routinely performed without being independently mandated throughout the UK. HIV RNA and HBV DNA are important examples because they are included in commercial triplex nucleic acid testing systems. [web:28]

1. Blood donation screening

Infectious agent	Screening test and classification	Important qualification
HIV-1/2, including group O	Anti-HIV-1/2/O or combined HIV-1/2/O antigen/antibody: mandatory. HIV RNA is routinely included in triplex NAT.	HIV RNA is specifically mandated in Scotland, but is not independently mandatory in most of the UK. Validated molecular pools may contain up to 24 donations.
Hepatitis B virus	HBsAg: mandatory. HBV DNA is routinely included in triplex NAT. Anti-HBc, with anti-HBs assessment where relevant: classified as additional in the published table.	All blood donors are nevertheless to undergo anti-HBc screening at the specified points described below. HBV DNA molecular pools may contain up to 24 donations.
Hepatitis C virus	Anti-HCV and HCV RNA: both mandatory.	Validated HCV RNA pools may contain up to 24 donations.
Syphilis	Anti-treponemal antibodies: mandatory.	Treponemal antibody screening, not a non-treponemal test alone.
HTLV-I/II	Anti-HTLV-I/II: mandatory in specified circumstances.	Required for previously untested donors and donations intended for non-leucodepleted products. Screening may be individual or in validated pools of up to 24 donations.
Hepatitis E virus	HEV RNA: mandatory.	Validated molecular pools may contain up to 24 donations.
Cytomegalovirus	Anti-CMV: additional.	Ideally IgG and IgM; IgG alone is considered sufficient by JPAC.
Malaria	Anti-Plasmodium falciparum/vivax: additional.	Apply the relevant donor-selection and geographical-risk guidance.
Trypanosoma cruzi	Anti-T. cruzi: additional.	Risk-based screening for Chagas disease.
West Nile virus	WNV RNA: additional.	Maximum validated pool size: 16 donations.
Hepatitis A virus	HAV RNA: additional.	Relevant to particular donation/product requirements; validated pools of up to 96 donations. Do not interpret this as universal routine testing of all blood components.
Human parvovirus B19	B19 DNA: additional.	Relevant to particular donation/product requirements; validated pools of up to 96 donations. Do not interpret this as universal routine testing of all blood components.

Source: JPAC Red Book, section 9.2, Table 9.1. Pool sizes are validated maxima in the cited table, not an instruction to use that pool size for every service or assay. [web:28]

Hepatitis B: anti-HBc screening schedule

All blood donors should be screened for anti-HBc:

At their first donation, or their first donation after the introduction of anti-HBc screening.
Again after a lapse in donation of more than two years.
Again if a new HBV risk is identified. [web:28]

UK anti-HBc screening was rolled out in 2022 to reduce the risk from occult HBV infection. This risk is not captured by residual-risk estimates that consider acute window-period infection alone. [web:5]

Can an anti-HBc-positive blood donation be released?

A confirmed anti-HBc-positive blood donation may be considered suitable for release if:

HBsAg is negative;
individual-donation HBV DNA is negative; and
anti-HBs is greater than 100 mIU/mL, measured within the preceding 24 months by a UK Blood Service. [web:28]

Do not use an anti-HBs concentration above 100 mIU/mL as a stand-alone release criterion. The HBsAg result, individual-donation NAT result and timing of the anti-HBs measurement also matter.

The published blood-donation criterion uses >100 mIU/mL. Tissue/cell wording and pathways differ; do not interchange the thresholds or release rules. These are donation-release criteria, not hepatitis B vaccination-response criteria. [web:28]

2. Residual risk after blood donation screening

Residual risk is the estimated probability that a potentially infectious donation made during the infectious window period escapes screening and may enter the blood supply. It is not the same as the probability that a recipient acquires infection. [web:5]

Latest verified UK estimates

The September 2025 JPAC position statement uses UK whole-blood donation data for 2022–2024. The following are estimates for all donors combined, expressed per million donations tested. [web:5]

Virus	Screening strategy assumed	Assumed infectious window period	Potentially infectious window-period donations not detected per million donations
HBV	HBsAg and HBV DNA NAT	30 days	1.09; 95% CI 0.63–3.35
HCV	Anti-HCV and HCV RNA NAT	4 days	<0.01
HIV	Combined HIV antigen/antibody testing and HIV NAT	9 days	0.10; see confidence-interval qualification below

All molecular screening in the model was performed on pools of 24 donations. These window periods are modelling assumptions for the stated strategies, not universal diagnostic window periods for clinical testing. [web:5]

The source has an internal inconsistency in the HIV confidence interval: the narrative reports 0.04–0.28 per million, whereas Table 1 reports 0.04–0.17 for all donors. The point estimate is consistently 0.10 per million. The discrepancy should be retained as a qualification rather than silently selecting one interval. [web:5]

Interpretation and limitations

HBV has the highest modelled window-period residual risk among these three viruses.
The HBV estimate covers acute infections only and excludes occult HBV infection. Anti-HBc screening addresses an additional source of risk.
No HCV seroconversions were detected in the 2022–2024 dataset. The reported estimate is <0.01 per million, not zero.
The figures are estimates of missed potentially infectious donations, not observed transfusion-transmission rates.
The 2022–2024 estimates are specifically for whole-blood donations. Donations of convalescent plasma and plasma for medicines are excluded and follow different testing and processing requirements.
HEV risk is not routinely estimated with the same rolling incidence/window-period method because its window period is uncertain and incidence fluctuates. Its absence from the table does not imply absence of risk. [web:5]

3. Tissue and stem-cell donation screening

The following summarises the published JPAC section 9.2 tissue/stem-cell table. It does not replace product-specific donor-selection guidance or transplant standards. Requirements for deceased tissue, living tissue, cord blood and haematopoietic progenitor cells need to be checked separately. [web:28]

Infectious agent	Tissue-donation screening	Stem-cell qualification
HIV	Anti-HIV-1/2/O or combined antigen/antibody: mandatory. HIV RNA: optional in the general tissue table.	The table specifies “as for blood donors” for HIV RNA.
HBV	HBsAg and anti-HBc: mandatory. Anti-HBs and HBV DNA have roles in the applicable assessment/release pathway.	HBsAg and HBV DNA: as for blood donors. Anti-HBc remains mandatory.
HCV	Anti-HCV: mandatory. HCV antigen and/or combined antigen/antibody, and HCV RNA: optional in the general tissue table.	The table specifies “as for blood donors” for HCV RNA.
Syphilis	Anti-treponemal antibodies: mandatory.	Mandatory.
HTLV-I/II	Anti-HTLV-I/II: mandatory, except that it is not mandatory for avascular tissues, although it may be good practice.	Apply the relevant stem-cell requirements.
HEV	HEV RNA: additional.	Apply the applicable donation-specific requirements.
CMV	Anti-CMV: additional. Ideally IgG and IgM; IgG alone is considered sufficient.	Apply the relevant transplant programme’s requirements.
Malaria	Malaria antibodies and, in specified pathways, malaria DNA: additional.	Certain tissues and cord blood from antibody-positive donors may be releasable if the relevant guidance permits and malaria DNA is not detected.
T. cruzi	Anti-T. cruzi: additional.	Risk-based.
WNV	WNV RNA: additional.	Risk-based.

Source: JPAC Red Book, section 9.2, Table 9.2 and its footnotes. “Optional” in a general tissue pathway must not be read as permission to omit a test required by a stem-cell standard or a particular transplant programme. [web:28]

Anti-HBc-positive tissue and stem-cell donations

The published table contains different release routes from the blood-donation pathway. In particular, anti-HBc-reactive tissue and stem-cell donations do not require an anti-HBs concentration of at least 100 mIU/mL to be considered suitable for release if both HBsAg and individual-donation HBV NAT are negative. [web:28]

The stem-cell donor-selection guidance also states that anti-HBc testing remains a regulatory requirement and that anti-HBs is not required where HBsAg and HBV DNA are negative. Some international registries may have additional requirements. [web:31]

Individual testing and pooling

All screening of deceased tissue donations should be performed on individual samples.
Anti-HTLV-I/II screening of surgical tissue/stem-cell donations may use validated pools of up to 24 samples.
HEV RNA screening of surgical tissues may use validated pools of up to 24 samples.
The specified maximum validated WNV RNA pool size is 16 donations.
Individual-donation HBV NAT is required for the anti-HBc-positive release pathway described above. [web:28]

Do not retain the old blanket statement that HIV/HCV RNA and anti-HTLV testing of all surgical tissue/stem-cell donations can be performed in pools of 24. The applicable test, donation type and current product-specific requirements must be distinguished.

Quarantine and follow-up testing

For applicable tissue-donation pathways, genomic screening for HIV, HCV and HBV on the original donation sample can replace 180 days of quarantine and follow-up serology. This is not a universal quarantine rule for all tissues or stem-cell collections. [web:28]

Deceased neonatal and infant tissue donors

JPAC specifies:

Full microbiology screening of a maternal sample is always required.
For stillbirths and neonates up to 28 days after birth, microbiology screening of the neonate is not required.
For infants more than 28 days after birth, full microbiology screening of an infant sample is also required. [web:28]

Additional transplant-related tests

Other tests, such as EBV or toxoplasma testing, may be required because of an identifiable risk, recipient requirements or product-specific standards. Exported products may also have additional end-user requirements. [web:28]

JPAC recommends Toxoplasma gondii IgG and IgM screening for haematopoietic stem cells, donor lymphocyte infusions and specified other therapeutic-cell products. Use of IgM-positive donors should be avoided. Isolated toxoplasma IgM reactivity should be confirmed because of recognised specificity limitations. [web:28]

4. What happens when a screen is reactive?

Screen-reactive is not synonymous with confirmed infection. Donation suitability and donor diagnosis are related but separate decisions. [web:28]

Blood-donation serology

For a donation initially reactive for the first time:

Repeat the sample in duplicate using the same screening assay.
The donation can be considered suitable for clinical use only if both repeat tests are negative and all other release requirements are met.
If either repeat test is reactive, the donation is unsuitable for transfusion and must be labelled appropriately as a biological hazard/not for transfusion.
Investigate the reactivity through the designated reference-laboratory pathway. [web:28]

For donors already investigated and shown to have non-specific reactivity, JPAC permits a defined alternative-assay screening pathway using an assay of at least equal sensitivity. This is not an ad hoc means of overriding a reactive result. [web:28]

Tissue and stem-cell serology

Initially reactive samples are retested in duplicate using either the same assay or an appropriately evaluated alternative of at least equal sensitivity, ideally using different antigens, antibodies or principles.

A donation non-reactive in both repeat tests may be considered suitable for use. Repeat-reactive tissue/stem-cell donations may sometimes be usable in defined clinical circumstances, depending on confirmatory results and the relevant guidance. This is not the routine blood-donation pathway. [web:28]

Molecular screening

Initially reactive NAT pools must be resolved to identify the reactive donation or donations. Other non-reactive donations may be considered suitable for release if all other requirements are satisfied.

Individual NAT-reactive blood donations are unsuitable for transfusion. Stem-cell donations from known infected individuals may occasionally be used in specific clinical circumstances under the applicable transplant pathway. [web:28]

Confirmation and donor follow-up

Reactive mandatory or additional serological/molecular screens require confirmatory testing at a designated reference laboratory; anti-CMV is excluded from this general confirmatory requirement. Confirmed positive results require arrangements to inform and appropriately advise the donor. [web:28]

JPAC’s published section 9.2 describes temporary exclusions of six months after a confirmed HEV, HAV or WNV RNA-positive donation, and four weeks after a confirmed B19 DNA-positive donation. Actual reinstatement must follow current section 9.4 and the relevant service procedure; these intervals are not a substitute for donor assessment. [web:28]

5. Assay performance and quality assurance

Use the current JPAC section 9.3 and the validated assay’s instructions for target-specific performance requirements. Donation screening is not simply interchangeable with routine diagnostic testing: the intended use, validation, quality control and any dilution from pooling matter. [web:28]

The previous version of this note contained a misaligned sensitivity table: it placed the HCV NAT statement against the wrong targets and also listed HCV RNA as having no specified minimum sensitivity. That table should not be retained.

A complete current section 9.3 could not be retrieved for this update. Numerical assay-sensitivity specifications have therefore deliberately not been reproduced as verified current requirements. This is a source-verification limitation, not a statement that no such requirements exist.

6. Travel-related and emerging infection risks

Use current JPAC donor-selection guidance and the Geographical Disease Risk Index when assessing travel and geographical exposure. Do not rely on a static country list in a revision note: the applicable risk classifications and donor requirements change. [web:17]

Additional testing must be interpreted together with the applicable eligibility rules. A negative test is not, by itself, permission to disregard a required deferral. The relevant donation type must also be identified: whole blood, tissue, cord blood and stem-cell rules may differ. [web:28]

7. Examination-focused summary

Point	Remember
Core blood-donation screens	HIV serology/combined antigen-antibody, HBsAg, anti-HCV plus HCV RNA, syphilis antibodies and HEV RNA; HTLV screening is mandatory in the specified circumstances.
HIV RNA and HBV DNA	Routinely included in triplex NAT; independent mandatory status is not identical throughout the UK. HIV RNA is mandated in Scotland.
Anti-HBc in blood donors	First donation/first donation after introduction; repeat after a lapse >2 years or a new HBV risk.
Anti-HBc-positive blood release	HBsAg negative, individual-donation HBV DNA negative, anti-HBs >100 mIU/mL measured by a UK Blood Service within 24 months.
Anti-HBc in tissue/stem-cell donors	Mandatory; the blood anti-HBs release rule must not be applied automatically.
HEV	Mandatory RNA screening for blood; additional in the cited tissue/stem-cell table.
HTLV	Blood: previously untested donors and non-leucodepleted products. Tissue: mandatory except the stated avascular-tissue exception.
Residual risk	Risk of an undetected potentially infectious donation, not the same as recipient transmission risk.
Highest modelled HBV/HCV/HIV window-period risk	HBV, in the verified 2022–2024 estimates.
Reactive screen	Requires the defined screening/confirmation pathway; does not establish infection by itself.

Screening summary: JPAC section 9.2. Residual-risk summary: JPAC September 2025 position statement. [web:28][web:5]

Source and currency notes

This update follows the published JPAC section 9.2 PDF retrieved for review, generated 12 March 2025, and the September 2025 residual-risk position statement. The live JPAC website showed later 2026 change notifications, but its section 9.2 HTML route did not expose the chapter text during retrieval. Accordingly, this document must not be described as verification of every screening-policy change through November 2026. The latest complete screening table that could be verified is the cited published PDF. [web:28][web:17]

JPAC Board minutes from November 2025 described work towards separate living-tissue, deceased-tissue and stem-cell screening tables. A proposed change or meeting discussion must not be treated as an implemented release requirement. Product-specific current guidance should be checked before clinical use. [web:8]

The latest residual-risk statement verified for this update is September 2025, using 2022–2024 data. It should be replaced when a later verified statement becomes available. [web:5]

Primary guidance links

The inline source markers identify the evidence used in preparing this update. The primary guidance links above provide portable source access when this Markdown document is used outside the original conversation.