Compared with an immediate-spin crossmatch, an antiglobulin (AHG) crossmatch also detects:

IgG antibodies to antigens on the donor red cells

ABO incompatibility between patient and donor

IgM cold antibodies such as anti-M and anti-P1

Antibodies in the donor plasma against the patient

What is mixed in the tube for an immediate-spin crossmatch?

Patient plasma with donor red cells

Donor plasma with patient red cells

Patient red cells with anti-A and anti-B

Patient plasma with group O screening cells

A group A patient's antibody screen (37 °C and AHG readings only) is negative. Immediate-spin crossmatches are 2+ with units 1 and 3 and negative with units 2 and 4; all are negative at 37 °C and AHG. All four units retype as group A, the autocontrol is negative, and the reverse grouping is negative with A1 cells. The most likely cause is:

A cold alloantibody such as anti-M

An IgG alloantibody such as anti-Jka

A cold autoantibody such as anti-I

Why is the minor crossmatch (donor plasma with patient red cells) no longer part of routine compatibility testing?

Donor plasma is screened for unexpected antibodies

Antibodies in donor plasma are always IgM

Patient red cells lack the antigens it detects

Donor red cells are always group O

When a validated computer system is used, an electronic crossmatch replaces which test?

The serologic immediate-spin crossmatch

The AHG crossmatch for patients with antibodies

Compatibility testing and crossmatch

18 DOH Abu Dhabi (HAAD) lab licensing practice questions on Compatibility testing and crossmatch, part of Blood Banking. The first 18 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 · Easy
Compared with an immediate-spin crossmatch, an antiglobulin (AHG) crossmatch also detects:
1. AABO incompatibility between patient and donor
2. BIgM cold antibodies such as anti-M and anti-P1
3. CIgG antibodies to antigens on the donor red cells
4. DAntibodies in the donor plasma against the patient
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Answer: C · IgG antibodies to antigens on the donor red cells
The AHG crossmatch incubates patient plasma with donor cells at 37 °C, washes them and adds antiglobulin reagent. This detects IgG antibodies, such as anti-Jka or anti-Fya, that coat donor cells without agglutinating them. It is required when the patient has, or has had, a clinically significant antibody. The immediate-spin crossmatch is designed only to detect ABO incompatibility.
- A: ABO incompatibility is already detected at immediate spin.
- B: Cold IgM antibodies react at room temperature, not mainly at the AHG phase.
- D: Antibodies in donor plasma are tested in the minor crossmatch, not the AHG crossmatch.
Question 2 · Easy
What is mixed in the tube for an immediate-spin crossmatch?
1. APatient plasma with donor red cells
2. BDonor plasma with patient red cells
3. CPatient red cells with anti-A and anti-B
4. DPatient plasma with group O screening cells
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Answer: A · Patient plasma with donor red cells
The major crossmatch mixes the patient's plasma or serum with red cells from a segment of the donor unit. In the immediate-spin version, the tube is centrifuged at room temperature straight away and read for agglutination or hemolysis. Because anti-A and anti-B are mostly IgM, this step detects ABO incompatibility. It does not detect most IgG alloantibodies, which need the antiglobulin phase.
- B: Donor plasma against patient cells is the minor crossmatch, which is no longer routine.
- C: Patient cells with anti-A and anti-B is forward ABO grouping.
- D: Patient plasma against group O screening cells is the antibody screen.
Question 3 · Hard
A group A patient's antibody screen (37 °C and AHG readings only) is negative. Immediate-spin crossmatches are 2+ with units 1 and 3 and negative with units 2 and 4; all are negative at 37 °C and AHG. All four units retype as group A, the autocontrol is negative, and the reverse grouping is negative with A1 cells. The most likely cause is:
1. AAn IgG alloantibody such as anti-Jka
2. BA cold autoantibody such as anti-I
3. CA cold alloantibody such as anti-M
4. DAnti-A1 in a group A2 patient
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Answer: C · A cold alloantibody such as anti-M
Reactions at immediate spin with only some ABO-correct units, and nothing at 37 °C or AHG, point to a cold alloantibody against an antigen on units 1 and 3, such as anti-M, anti-N, anti-P1 or anti-Lea. The screen missed it because it was read only at 37 °C and AHG. Anti-A1 is excluded by the negative reaction with A1 cells, and a cold autoantibody would make the autocontrol positive. Such antibodies are usually not clinically significant, so units compatible at 37 °C and AHG can normally be given once the antibody is identified.
- A: An IgG antibody such as anti-Jka would react at the AHG phase.
- B: A cold autoantibody would also react with the patient's own cells in the autocontrol.
- D: Anti-A1 is unlikely because the A1 reverse grouping cells do not react.
Question 4 · Medium
Why is the minor crossmatch (donor plasma with patient red cells) no longer part of routine compatibility testing?
1. AAntibodies in donor plasma are always IgM
2. BPatient red cells lack the antigens it detects
3. CDonor red cells are always group O
4. DDonor plasma is screened for unexpected antibodies
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Answer: D · Donor plasma is screened for unexpected antibodies
Blood centers test every donation for unexpected red cell antibodies, and red cell units contain little plasma after component preparation. Any passive antibody that remains is diluted further in the patient's circulation. AABB therefore does not require a minor crossmatch. The major crossmatch, patient plasma against donor cells, remains the key test.
- A: Donor antibodies can be IgG or IgM.
- B: Patient cells carry many antigens; that is not the reason.
- C: Donor units come in all ABO groups, not only group O.
Question 5 · Medium
When a validated computer system is used, an electronic crossmatch replaces which test?
1. AThe patient's ABO and D typing
2. BThe serologic immediate-spin crossmatch
3. CThe patient's antibody screen
4. DThe AHG crossmatch for patients with antibodies
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Answer: B · The serologic immediate-spin crossmatch
The electronic crossmatch is a computer check that the unit's confirmed ABO group is compatible with the patient's verified ABO group. It replaces the immediate-spin crossmatch, whose main job is the same ABO check. The antibody screen and patient typing must still be done, and the patient must have no current or past clinically significant antibodies. The system must also alert staff to discrepancies and block the issue of ABO-incompatible units.
- A: Patient ABO and D typing are needed for the computer check itself.
- C: The antibody screen must still be done and must be negative.
- D: Patients with clinically significant antibodies need an AHG crossmatch.
Question 6 · Medium
A 3-week-old infant in the neonatal unit had a negative antibody screen before the first red cell transfusion. For further group O red cell transfusions during the same admission, repeat crossmatching is:
1. ARequired every 3 days, like adult samples
2. BRequired before each unit, tested to the AHG phase
3. CRequired only if the mother is group O
4. DNot required while the infant is under 4 months
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Question 7 · Easy
After a transfusion, the patient's pretransfusion sample and a segment from each donor unit must be kept refrigerated for at least:
1. A3 days
2. B24 hours
3. C7 days
4. D30 days
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Question 8 · Hard
Which patient must have an antiglobulin crossmatch rather than an immediate-spin or electronic crossmatch?
1. AA man with a negative screen and no history of antibodies
2. BA woman with anti-c 3 years ago and a negative screen today
3. CA child with a negative screen whose ABO is confirmed twice
4. DA man whose anti-I autoantibody reacts only at room temperature
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Question 9 · Hard
A patient's plasma contains anti-Lea, reacting only at immediate spin, and anti-Jkb, reacting at the antiglobulin phase. Which units and crossmatch are appropriate?
1. AJk(b-) units, issued by electronic crossmatch
2. BRandom units, compatible at immediate spin
3. CLe(a-) units, compatible at immediate spin
4. DJk(b-) units, compatible by AHG crossmatch
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Question 10 · Hard
A patient has anti-E, anti-K and anti-Jkb and needs 2 red cell units. In this donor population, E is found in 30%, K in 9% and Jkb in 74% of donors. About how many random units must be screened to find 2 that are negative for all three antigens?
1. AAbout 6
2. BAbout 3
3. CAbout 12
4. DAbout 100
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Question 11 · Hard
A 2-week-old group O, D-positive infant needs red cells. The mother has anti-c, and the infant's plasma reacts with c-positive cells at the antiglobulin phase. Which red cells should be given?
1. AGroup O, D-negative units, issued by electronic crossmatch
2. BGroup O, c-positive units, compatible at immediate spin
3. CGroup O units with no crossmatch, as the infant is under 4 months
4. DGroup O, c-negative units, compatible by AHG crossmatch
Answer and explanation in LearnFree account
Question 12 · Hard
An immediate-spin crossmatch uses fresh serum; the serum and the donor cell suspension were clear before mixing. After centrifugation the supernatant is pink, the cell button is smaller than in the other tubes, and no agglutinates are seen. How should it be interpreted?
1. AInvalid, because the donor segment was hemolyzed
2. BWeakly positive, so it should be read at AHG
3. CCompatible, because no agglutination is seen
4. DIncompatible, because hemolysis is a positive result
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Question 13 · Medium
Before red cell units received from the blood supplier are used, the hospital blood bank must retest a segment to confirm:
1. AABO and D of every unit, and an antibody screen
2. BOnly the D type of every unit
3. CABO of every unit and D of units labeled D-negative
4. DWeak D status of every unit labeled D-positive
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Question 14 · Hard
A 67-year-old woman is booked for a knee replacement. She received 2 red cell units after a fall 4 months ago at another hospital. Today she types group A, D-positive, and her antibody screen is negative by gel antiglobulin test with a two-cell screen in which both cells type Jk(a+b+). Her own red cells type Jk(a-b+). Antiglobulin crossmatches with four group A units: unit 1, 1+; units 2, 3 and 4, negative. Unit 1 types Jk(a+b-), unit 2 Jk(a+b+), and units 3 and 4 Jk(a-b+). A DAT on a segment from unit 1 is negative. The most likely explanation for the incompatible crossmatch is:
1. ADonor red cells coated with IgG
2. BAntibody to a low-prevalence antigen
3. CA cold autoantibody in her plasma
4. DWeak anti-Jka showing dosage
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Question 15 · Hard
A 300-bed hospital in Abu Dhabi reviews one month of blood orders for two elective operations. Laparoscopic cholecystectomy: 50 patients, 100 red cell units crossmatched by the antiglobulin method and held for 48 hours, 4 units transfused. Total hip replacement: 40 patients, 70 units crossmatched, 42 units transfused. All patients had a negative antibody screen, and the laboratory has a validated system for electronic crossmatch on demand. The hospital's target crossmatch-to-transfusion (C:T) ratio is 2.0 or less. Which operation should move to type and screen only, and why?
1. AHip replacement; its C:T ratio is 1.7
2. BBoth; each orders about 2 units per patient
3. CCholecystectomy; its C:T ratio is 25
4. DNeither; both C:T ratios are below 2.0
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Question 16 · Medium
A patient was transfused 4 weeks ago. Within how many days of the planned transfusion must the pre-transfusion sample be collected?
1. A30 days
2. B14 days
3. C3 days
4. D7 days
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Question 17 · Medium
A patient has anti-E. Which red cell units should be selected?
1. AAny group O unit, without antigen typing
2. BE-negative units, compatible by AHG crossmatch
3. CE-positive units, compatible at immediate spin
4. DWashed units without antigen typing
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Question 18 · Hard
The antibody screen is negative, but one donor unit is incompatible in the antiglobulin crossmatch. What is the most likely explanation?
1. AAntibody to a low-prevalence antigen, or a DAT-positive unit
2. BAnti-D present in the donor unit's plasma
3. CAn ABO grouping error in the patient's sample
4. DA cold autoantibody, such as anti-I, in the patient's plasma
Answer and explanation in LearnFree account

Compatibility testing and crossmatch

Compared with an immediate-spin crossmatch, an antiglobulin (AHG) crossmatch also detects:

What is mixed in the tube for an immediate-spin crossmatch?

Why is the minor crossmatch (donor plasma with patient red cells) no longer part of routine compatibility testing?

When a validated computer system is used, an electronic crossmatch replaces which test?

A 3-week-old infant in the neonatal unit had a negative antibody screen before the first red cell transfusion. For further group O red cell transfusions during the same admission, repeat crossmatching is:

After a transfusion, the patient's pretransfusion sample and a segment from each donor unit must be kept refrigerated for at least:

Which patient must have an antiglobulin crossmatch rather than an immediate-spin or electronic crossmatch?

A patient's plasma contains anti-Lea, reacting only at immediate spin, and anti-Jkb, reacting at the antiglobulin phase. Which units and crossmatch are appropriate?

A patient has anti-E, anti-K and anti-Jkb and needs 2 red cell units. In this donor population, E is found in 30%, K in 9% and Jkb in 74% of donors. About how many random units must be screened to find 2 that are negative for all three antigens?

A 2-week-old group O, D-positive infant needs red cells. The mother has anti-c, and the infant's plasma reacts with c-positive cells at the antiglobulin phase. Which red cells should be given?

An immediate-spin crossmatch uses fresh serum; the serum and the donor cell suspension were clear before mixing. After centrifugation the supernatant is pink, the cell button is smaller than in the other tubes, and no agglutinates are seen. How should it be interpreted?

Before red cell units received from the blood supplier are used, the hospital blood bank must retest a segment to confirm:

A patient was transfused 4 weeks ago. Within how many days of the planned transfusion must the pre-transfusion sample be collected?

A patient has anti-E. Which red cell units should be selected?

The antibody screen is negative, but one donor unit is incompatible in the antiglobulin crossmatch. What is the most likely explanation?