A patient's screen and autocontrol are negative. One of four units is 2+ incompatible in the AHG crossmatch; the others are compatible. Which test should be done first?

A DAT on the incompatible donor unit's cells

A slow infusion of the unit to watch for reactions

An eluate from the patient's red cells

A repeat screen incubated at 4 °C

A patient with anti-K needs 2 red cell units. The crossmatch must:

Use K-negative units, tested to the AHG phase

Be electronic, with K-negative units

Use any units, tested at immediate spin

Be skipped entirely if the units are K-negative

A trauma patient known to have anti-K is bleeding heavily. The physician requests blood before compatibility testing can be finished. What is best?

Group O, K-negative units now; crossmatch later

Any group O units, with no record kept

No blood until a full crossmatch is complete

Group AB units, as they lack K antigen

Which conditions allow an electronic (computer) crossmatch?

No history of significant antibodies; two ABO checks

A serologic crossmatch done within the last 30 days

A negative DAT on the current sample

A group O patient's immediate-spin crossmatch is 3+ with one group O unit and compatible with three others. The antibody screen is negative. What is the most likely cause?

The unit's ABO group is mislabeled

A cold autoantibody in the patient

A low-prevalence antibody in the patient

Routine tests: crossmatch

7 ASCP MLS practice questions on Routine tests: crossmatch, part of Blood Banking. The first 7 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

Question 1 · Hard
A patient's screen and autocontrol are negative. One of four units is 2+ incompatible in the AHG crossmatch; the others are compatible. Which test should be done first?
1. AA slow infusion of the unit to watch for reactions
2. BAn eluate from the patient's red cells
3. CA DAT on the incompatible donor unit's cells
4. DA repeat screen incubated at 4 °C
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Answer: C · A DAT on the incompatible donor unit's cells
If the donor's own red cells are coated with IgG, they react with anti-human globulin in any crossmatch, whatever the patient's plasma contains. A positive DAT on a segment from the unit confirms this; the unit is not used and the supplier is told. If the donor DAT is negative, an antibody to a low-prevalence antigen on that unit is the next explanation. Either way, another compatible unit is chosen.
- A: An incompatible unit should not be transfused.
- B: The patient's autocontrol is negative, so an eluate is not useful.
- D: Clinically significant antibodies are not found at 4 °C.
Question 2 · Medium
A patient with anti-K needs 2 red cell units. The crossmatch must:
1. AUse K-negative units, tested to the AHG phase
2. BBe electronic, with K-negative units
3. CUse any units, tested at immediate spin
4. DBe skipped entirely if the units are K-negative
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Answer: A · Use K-negative units, tested to the AHG phase
When a patient has, or has had, a clinically significant antibody, red cells must lack the antigen and be compatible in an antiglobulin crossmatch. The AHG crossmatch can also catch an antibody not yet identified. K-negative units are easy to find, because about 91% of donors are K-negative. The units' antigen-negative status is confirmed with antisera when available.
- B: Electronic crossmatch is not allowed when a significant antibody is present.
- C: Immediate spin does not detect IgG anti-K.
- D: An antiglobulin crossmatch is still required.
Question 3 · Hard
A trauma patient known to have anti-K is bleeding heavily. The physician requests blood before compatibility testing can be finished. What is best?
1. AGroup O, K-negative units now; crossmatch later
2. BAny group O units, with no record kept
3. CNo blood until a full crossmatch is complete
4. DGroup AB units, as they lack K antigen
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Answer: A · Group O, K-negative units now; crossmatch later
In an emergency, the physician signs for uncrossmatched blood, and the blood bank gives the safest units available. Group O red cells avoid ABO problems, and K-negative units protect against the known anti-K. Compatibility testing is completed afterwards, and the physician is told at once of any incompatibility. Delaying blood in massive bleeding is more dangerous than these remaining risks.
- B: Emergency release must be documented, and the known antibody should be respected when possible.
- C: Waiting for a full crossmatch can be fatal in massive bleeding.
- D: K antigen is unrelated to ABO group, and group AB red cells cannot go to every patient.
Question 4 · Medium
Which conditions allow an electronic (computer) crossmatch?
1. AA serologic crossmatch done within the last 30 days
2. BA negative DAT on the current sample
3. CGroup O red cells being issued
4. DNo history of significant antibodies; two ABO checks
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Answer: D · No history of significant antibodies; two ABO checks
An electronic crossmatch replaces serologic testing only when the patient has no clinically significant antibodies, now or in the past. The patient's ABO group must be confirmed by two determinations, one on the current sample and another by retesting, a second sample or a record. The computer system must be validated and must alert on ABO incompatibility between unit and patient. Donor units must have had their ABO group confirmed.
- A: An earlier crossmatch does not replace the current requirements.
- B: A negative DAT is not a requirement for electronic crossmatch.
- C: Electronic crossmatch is used for group-specific units, not only group O.
Question 5 · Hard
A group O patient's immediate-spin crossmatch is 3+ with one group O unit and compatible with three others. The antibody screen is negative. What is the most likely cause?
1. AAnti-A1 in a group O patient
2. BThe unit's ABO group is mislabeled
3. CA cold autoantibody in the patient
4. DA low-prevalence antibody in the patient
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Answer: B · The unit's ABO group is mislabeled
The immediate-spin crossmatch is mainly a check for ABO incompatibility, and a strong reaction with one unit suggests the unit is not group O. The unit is quarantined, retyped and reported to the supplier. A cold autoantibody would react with every unit and the autocontrol. An antibody to a low-prevalence antigen is possible but is a less likely cause of a strong immediate-spin reaction.
- A: Group O patients have anti-A and anti-A1, which do not react with genuine group O cells.
- C: A cold autoantibody would react with all units and the autocontrol.
- D: Possible, but a strong immediate-spin reaction with a group O unit points first to an ABO error.
Question 6 · Hard
A 61-year-old group A, D-positive woman with leukemia received two group O apheresis platelet units over the past 24 hours because group A platelets were not available. Today both group A red cell units crossmatched for her are incompatible (immediate spin 1+, antiglobulin 2+), while two group O units are compatible. Her red cells react 4+ with anti-A and with anti-A1 lectin; in the reverse grouping, A1 cells react 1+ and B cells 4+. The antibody screen is negative, and the DAT is weakly positive with anti-IgG. What is the most likely cause?
1. AAnti-A1 made by an A2 patient
2. BAntibody to a low-prevalence antigen
3. CWarm autoantibody with A specificity
4. DPassive anti-A from the platelet plasma
Answer and explanation in LearnFree account
Question 7 · Easy
When the antibody screen is negative, what is the immediate-spin crossmatch mainly a check for?
1. AABO incompatibility between donor and patient
2. BClinically significant IgG antibodies
3. CPlatelet antibodies
4. DRh antibodies only
Answer and explanation in LearnFree account