Donor infectious disease testing

10 DOH Abu Dhabi (HAAD) lab licensing practice questions on Donor infectious disease testing, part of Blood Banking. The first 10 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

1. Question 1 · Medium

   Donor results: HBsAg nonreactive; total anti-HBc reactive; IgM anti-HBc nonreactive; HBV DNA detected at a low level. These results fit best with:

   1. AResponse to hepatitis B vaccination
   2. BOccult hepatitis B infection
   3. CEarly infection, before HBsAg appears
   4. DResolved infection with immunity

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   Answer: B · Occult hepatitis B infection

   HBV DNA in the blood without detectable HBsAg, outside the early window period, defines occult hepatitis B infection. Anti-HBc shows past exposure, and the negative IgM anti-HBc argues against a recent acute infection. Such donations can transmit HBV, which is why anti-HBc testing and sensitive NAT are used. The unit is discarded, and the donor is deferred and referred for follow-up.

   • A: Vaccination gives anti-HBs only, not anti-HBc or HBV DNA.
   • C: In early infection anti-HBc is not yet present, and HBsAg soon follows HBV DNA.
   • D: A fully resolved infection would not have HBV DNA in the blood.

2. Question 2 · Easy

   HTLV-I and HTLV-II are passed on by transfusion mainly through:

   1. ACellular components with live lymphocytes
   2. BFresh frozen plasma from single donors
   3. CCryoprecipitate pooled from several donors
   4. DFractionated albumin and immunoglobulin

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   Answer: A · Cellular components with live lymphocytes

   HTLV lives inside T lymphocytes and is cell-associated, so it is transmitted by red cells, platelets and whole blood that contain viable lymphocytes. Cell-free plasma products such as FFP and cryoprecipitate have not been shown to transmit it. Leukocyte reduction and longer storage lower the risk further. Donors are screened for anti-HTLV-I/II, since HTLV-I can cause adult T-cell leukemia/lymphoma and a myelopathy.

   • B: Fresh frozen plasma is essentially cell-free and does not transmit HTLV.
   • C: Cryoprecipitate is a cell-free plasma product.
   • D: Fractionated products are cell-free and treated during manufacture to inactivate viruses.

3. Question 3 · Hard

   In a donor population, HIV incidence among repeat donors is 4 per 100,000 person-years. With NAT, the infectious window period is about 9 days. Using residual risk = incidence × window period, the estimated risk per donation is about:

   1. A1 in 145,000
   2. B1 in 1,000,000
   3. C1 in 33,000
   4. D1 in 2,800

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   Answer: B · 1 in 1,000,000

   Convert the window period to years: 9 ÷ 365 = 0.0247 year. Multiply by the incidence: 0.00004 per year × 0.0247 year = about 0.00000099, or about 1 in 1,000,000 donations. The model estimates the chance that an infected donor gives blood during the window, when the tests are still negative. Shorter window periods (more sensitive NAT) and lower incidence both reduce the residual risk.

   • A: 1 in 145,000 comes from dividing the 9 days by 52, as if they were weeks.
   • C: 1 in 33,000 comes from dividing by 12, as if the window were 9 months.
   • D: 1 in 2,800 comes from multiplying by 9 days without converting them to years.

4. Question 4 · Easy

   Many blood services screen donors for syphilis with a treponemal antibody immunoassay. Which test, also treponemal, is often used to confirm a reactive screen?

   1. ARPR (rapid plasma reagin)
   2. BVDRL (slide flocculation)
   3. CUSR (unheated serum reagin)
   4. DTPPA (particle agglutination)

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   Answer: D · TPPA (particle agglutination)

   Treponemal tests detect antibody to Treponema pallidum antigens, while RPR, VDRL and USR are nontreponemal tests that detect antibody to cardiolipin. A reactive treponemal screen is usually checked with a second, different treponemal test such as TPPA, often with an RPR to judge activity. Treponemal antibodies usually stay positive for life, even after treatment. Syphilis testing also serves as a marker of sexual risk in donors.

   • A: RPR detects antibody to cardiolipin, not to treponemal antigens.
   • B: VDRL is a nontreponemal cardiolipin test.
   • C: USR is a nontreponemal test like the RPR.

5. Question 5 · Medium

   A donor is anti-HCV repeat reactive, but HCV RNA is not detected by NAT on the same sample. Which interpretation fits?

   1. AProtection from earlier HCV vaccination
   2. BAcute HCV infection in the window period
   3. CResolved past infection or a false-positive antibody
   4. DChronic HCV infection with ongoing viremia

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   Answer: C · Resolved past infection or a false-positive antibody

   A reactive antibody with no detectable RNA means either a past infection that has cleared, which happens in roughly 15 to 45% of infected people, or a false-positive screening result. A supplementary test, such as a different antibody assay, helps to tell these apart. The unit is discarded either way, and the donor is deferred and counselled according to the centre's algorithm. In window-period infection the pattern is the reverse: RNA positive and antibody negative.

   • A: There is no licensed HCV vaccine.
   • B: In the window period RNA is positive and antibody is still negative.
   • D: Chronic infection with viremia would show HCV RNA.

6. Question 6 · Easy

   A fourth-generation HIV combination immunoassay used for donor screening detects:

   1. AHIV-1 RNA and HIV-1 proviral DNA
   2. BHIV-1/2 antibodies and HIV-1 p24 antigen
   3. CHIV-1 p24 antigen but not antibodies
   4. DHIV-1 antibodies but not HIV-2 antibodies

   Answer and explanation in LearnFree account

7. Question 7 · Hard

   A first-time donor has these results: HIV-1/2 antigen/antibody combination assay nonreactive; HIV-1 RNA reactive by individual-donation NAT, and reactive again on repeat; HBsAg, anti-HCV and syphilis tests nonreactive. The most likely explanation is:

   1. APast HIV-1 infection that has since resolved
   2. BHIV-2 infection missed by the combination assay
   3. CEarly HIV-1 infection, before p24 antigen or antibody appear
   4. DAn expected result after HIV vaccination

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8. Question 8 · Easy

   After infection with hepatitis B virus, which marker becomes detectable in a donor's blood first?

   1. AIgM anti-HBc
   2. BHBV DNA
   3. CAnti-HBs
   4. DHBsAg

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9. Question 9 · Medium

   A minipool of 16 donor samples is reactive for HCV RNA by NAT. What happens next?

   1. AThe units are released if anti-HCV is nonreactive
   2. BAll 16 units are discarded and their donors deferred
   3. CThe pool is retested and released if then nonreactive
   4. DEach sample in the pool is tested individually

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10. Question 10 · Hard

    A 38-year-old repeat donor gives whole blood at a UAE blood service. Today's results: HCV RNA reactive by individual-donation NAT after a reactive minipool, viral load 3.2 × 10^6 IU/mL; anti-HCV nonreactive; HBsAg, HIV-1/2 antigen/antibody, HBV DNA and HIV-1 RNA nonreactive; ALT 96 U/L (reference below 45). His earlier donations, with all tests nonreactive: 11 weeks ago, red cells transfused 9 weeks ago and plasma still frozen in stock; 3 years ago, all components transfused. The service's lookback covers donations made in the 12 months before a donor's last nonreactive test. Besides discarding today's unit and deferring the donor, what should be done?

    1. ATrace and notify recipients of both earlier donations
    2. BNo lookback; both earlier donations tested nonreactive
    3. CWait for anti-HCV to turn reactive, then start lookback
    4. DQuarantine the 11-week plasma; trace the red cell recipient

    Answer and explanation in LearnFree account