Board Prep: Overview of Donor Infectious Disease Eligibility

Donor infectious disease eligibility is one of those topics that feels straightforward until you’re asked to explain why a donor with negative testing still isn’t eligible — or why some pathogens get NAT, others don’t, and some only get tested once.

This post walks through donor eligibility the way the boards expect you to understand it: as a risk-assessment framework, not just a checklist of tests.

What Is Donor Infectious Disease Eligibility?

Donor eligibility is the assessment of a donor’s risk of transmitting infectious disease to a recipient. Its purpose is recipient protection and it is based on two pillars:

1. Donor history

2. Laboratory testing

   
   

This is distinct from donor suitability, which focuses on donor safety (for example, hemoglobin thresholds or procedural tolerance). A donor can be suitable but not eligible — and vice versa.

How Donor Eligibility Is Determined

The Donor History Questionnaire (DHQ)

The DHQ evaluates risks that laboratory testing alone cannot fully capture, including:

• Symptoms of infection

• Behavioral risk factors

• Travel and residence history

• Exposure history (blood, needles, sexual contact)

  
  

Testing does not eliminate window-period risk, and emerging pathogens may not yet have validated screening assays. As a result, negative testing does not equal eligibility when exposure risk is recent.

The Window Period (Why History Still Matters)

The window period is the time between infection and when that infection becomes detectable by testing.

Even with modern NAT-based screening, window periods still exist. This is why donor history remains a critical component of eligibility determination.

Infectious Disease Screening: The Tests (What We Use and Why)

All allogeneic donors undergo infectious disease screening using serologic testing, nucleic acid testing (NAT), or both. The strategy used for each pathogen reflects its biology: duration of viremia, durability of antibody response, prevalence, and the clinical consequences of transmission.

HIV-1/2

Serology

• HIV-1/2 antibody

• HIV-1 p24 antigen

NAT

• HIV-1 RNA

Window Period

• NAT: 9–11 days

• Serology: 15–20 days

Notes

Layered NAT and Ag/Ab screening minimizes window-period transmission, making residual transfusion-transmitted HIV risk extremely low. However, there is no licensed HIV-2 NAT test in the U.S., so HIV-2 detection relies entirely on serology.

Hepatitis B Virus (HBV)

Serology

• HBsAg

• Anti-HBc

NAT

• HBV DNA

Window Period

• NAT: 20–22 days

• Serology: 30–38 days

Notes

HBV has the longest residual transfusion risk among routinely screened viral infections due to low-level, intermittent viremia. Triple-layer testing mitigates occult and low-level infection but does not eliminate risk entirely.

Hepatitis C Virus (HCV)

Serology

• Anti-HCV

NAT

• HCV RNA

Window Period

• NAT: 3–5 days

• Serology: 50–70 days

Notes

Universal NAT has nearly eliminated window-period HCV transmission. Anti-HCV testing is notorious for false positives, which is why donor re-entry policies matter.

HTLV-I/II

Serology

• Anti-HTLV-1/2

NAT

• Not performed

Window Period

• Serology: 45–60 days

Notes

HTLV infection is chronic with a durable antibody response, enabling serology-only screening. HTLV-1 is associated with adult T-cell leukemia/lymphoma. The screening strategy reflects low prevalence, not a short window period.

West Nile Virus (WNV)

Serology

• Not performed

NAT

• WNV RNA

Window Period

• NAT: 6–10 days

Notes

Short viremia necessitates NAT-only, seasonally adaptive screening. Serology is not useful for donor screening in acute infection.

Syphilis (Treponema pallidum)

Serology

• Treponemal antibody test

• Non-treponemal test

NAT

• Not performed

Window Period

• Serology: 10–30 days

Notes

T. pallidum survives poorly in refrigerated blood, making transfusion transmission rare but documented. Treponemal antibodies persist long after infection and treatment, which is why syphilis is a key context for donor re-entry.

Trypanosoma cruzi (Chagas Disease)

Serology

• Antibody testing only

NAT

• Not performed

Window Period

• Serology: 3–8 weeks

Notes

Chronic infection with durable antibodies enables one-time serologic screening. Transmission is rare but serious and linked to donors with residence in endemic areas.

Babesia

Serology

• Not performed

NAT

• Babesia DNA

Window Period

• NAT: 7–14 days

Notes

Persistent asymptomatic parasitemia necessitates regional NAT screening. Babesia is a leading cause of fatal transfusion-transmitted infection in the U.S., with required testing in endemic regions including the Northeast and Upper Midwest.

Deferrals: Temporary vs Indefinite

• Temporary deferrals apply when risk decreases with time

• Indefinite deferrals apply when risk does not meaningfully decrease

Examples include:

• Temporary: recent tattoo, recent exposure, acute illness

• Indefinite: HIV, chronic HBV, HCV, HTLV, vCJD risk

  
  

High-Yield Deferral Periods (Boards Love These)

Some deferrals are particularly high yield because they test whether you understand current, risk-based policy rather than outdated rules.

Malaria

• Travel to endemic area (no illness): 3-month deferral

• Residence in endemic area or prior malaria: 2-year deferral

  
  

High-Risk Sexual Behavior or Injection Drug Use

• Universal 3-month deferral

• Applies regardless of gender or sexual orientation

  
  

Incarceration

• >72 hours: 12-month deferral

• <72 hours: No deferral

  
  

Tattoos

• State-licensed facility: No deferral

• Non-state-licensed facility: 3-month deferral

  
  

vCJD-Related Risks

• Residence in Great Britain or Europe: No deferral

• Use of bovine growth hormone: Indefinite deferral

• Cadaveric dura mater transplant: Indefinite deferral

  
  

Donor Eligibility Potpourri (The Real-World Stuff)

Donor Re-Entry

Donor re-entry allows individuals with false-positive screening tests to become eligible to donate again. This process:

• Is pathogen-specific

• Is regulated by the FDA

• Requires repeat testing on a subsequent donation

  
  

Confirmed infections generally preclude re-entry, with syphilis (after full treatment) being the main exception.

Product Look-Backs

Product look-backs occur when a donor is later found to have a positive infectious disease test. All donations during a defined prior period must be investigated to determine:

• Whether products were transfused

• Whether recipient notification or testing is required

  
  

For boards:

• Look-backs are mandated for HIV-1/2 and HCV

• The required look-back period is 12 months prior to the positive test

  
  

Special Donor Populations

Directed Donors

• Must meet the same infectious disease eligibility criteria

• No relaxation of standards

• If unused, products may be returned to general inventory

  
  

Autologous Donors

• Minimum hemoglobin: >11 g/dL

• Collection must occur >72 hours before surgery

• Requires physician order

• Infectious disease testing may vary by institutional policy

• If unused, products are discarded

  
  

Regulatory Oversight: Who Sets the Rules?

• FDA

  • Establishes laws and regulations

  • 21 CFR 630 governs donor infectious disease testing

• AABB

  • Interprets FDA regulations into operational standards

  • Maintains the Donor History Questionnaire

    
    

Understanding who regulates what matters — especially when policies change.

Consolidated Board Pearls

The Basics

• Define the window period → Time between infection and detection

• What does DHQ stand for? → Donor History Questionnaire

  
  

Infectious Disease Screening

• Name 3 pathogen classes not directly tested → Most bacteria, most parasites, prion diseases

  
  

Screening Tests

• Most common fatal transfusion-associated infection? → Babesia

• HIV-1/2 NAT window period? → 9–11 days

• Virus with longest residual transfusion risk? → HBV

  
  

Deferrals

• Universal deferral period for high-risk behavior? → 3 months

• Deferral for incarceration <72 hours? → None

• Deferral for cadaveric dura mater transplant? → Indefinite

  
  

Eligibility Potpourri

• Mandated look-back period for HIV? → 12 months

• What is donor re-entry? → Process allowing donors with false-positive tests to donate again

• If a directed unit is unused, must it be discarded? → No, it may enter general inventory