A patient with myeloma has stacked-coin clumps at immediate spin and 37 °C with all screening cells and the autocontrol, and they disperse when saline is added. Why can the antiglobulin phase of the same tubes still be read reliably?

Washing removes the plasma proteins causing rouleaux

Rouleaux form only below room temperature

Myeloma protein speeds up the AHG reaction

AHG breaks up stacked cells before reading

In a gel IAT, serum spun before it had fully clotted gives a thin line of cells at the top of the gel in every well, including the autocontrol, with most cells at the bottom. The most likely cause is:

Fibrin trapping some of the red cells

An alloantibody to a high-prevalence antigen

Too few red cells added to each well

Inadequate washing of the red cells

DAT results on a patient sample: anti-IgG 2+, anti-C3d 2+, saline control 2+. What should be done next?

Wash the cells in warm saline and repeat

Prepare an eluate from the red cells

Repeat using polyspecific AHG only

Report coating with both IgG and C3d

AHG reagents for the DAT contain anti-C3d rather than relying on anti-C3b alone. Why?

C3b on circulating cells is soon cut down to C3d

Anti-C3b would also react with IgG on the cells

C3d is the first complement fragment to bind

C3d activates the membrane attack complex

A new staff member incubates a saline IAT, with no enhancement medium, for 10 minutes, the time used for the LISS method. Why could a weak antibody be missed?

Saline tests need 30 to 60 minutes for binding

Saline destroys IgG during short incubations

AHG reacts only with LISS-sensitized cells

Ten minutes is so long that the IgG dissociates

Antiglobulin tests

14 DOH Abu Dhabi (HAAD) lab licensing practice questions on Antiglobulin tests, part of Blood Banking. The first 14 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 with myeloma has stacked-coin clumps at immediate spin and 37 °C with all screening cells and the autocontrol, and they disperse when saline is added. Why can the antiglobulin phase of the same tubes still be read reliably?
1. AWashing removes the plasma proteins causing rouleaux
2. BRouleaux form only below room temperature
3. CMyeloma protein speeds up the AHG reaction
4. DAHG breaks up stacked cells before reading
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Answer: A · Washing removes the plasma proteins causing rouleaux
Rouleaux are caused by high levels of plasma proteins, such as a paraprotein, that make red cells stick together like stacks of coins. Before AHG is added the cells are washed several times, which removes these proteins, so rouleaux cannot form at the antiglobulin phase. Readings at earlier phases can be checked by saline replacement. Rouleaux are also a common cause of extra reactions in reverse grouping.
- B: Rouleaux can form at room temperature and at 37 °C.
- C: Unwashed paraprotein would neutralize AHG; it does not speed up the reaction.
- D: AHG does not break up rouleaux; washing has already removed their cause.
Question 2 · Medium
In a gel IAT, serum spun before it had fully clotted gives a thin line of cells at the top of the gel in every well, including the autocontrol, with most cells at the bottom. The most likely cause is:
1. AAn alloantibody to a high-prevalence antigen
2. BToo few red cells added to each well
3. CInadequate washing of the red cells
4. DFibrin trapping some of the red cells
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Answer: D · Fibrin trapping some of the red cells
Serum separated before clotting is complete keeps forming fibrin in the well, and fibrin strands can hold red cells at the top of the gel. This looks like agglutination but is a false positive. A reaction with every cell, including the autocontrol, also argues against an alloantibody. The sample should be allowed to clot fully and be spun again, or EDTA plasma used.
- A: An alloantibody would not react with the patient's own cells in the autocontrol.
- B: Too few cells give a weak or hard-to-read result, not a line at the top.
- C: Gel tests need no washing, because the gel separates cells from unbound globulin.
Question 3 · Hard
DAT results on a patient sample: anti-IgG 2+, anti-C3d 2+, saline control 2+. What should be done next?
1. APrepare an eluate from the red cells
2. BWash the cells in warm saline and repeat
3. CRepeat using polyspecific AHG only
4. DReport coating with both IgG and C3d
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Answer: B · Wash the cells in warm saline and repeat
A positive saline control means the cells agglutinate without any AHG, so the IgG and C3d results cannot be interpreted. The usual cause is a cold IgM autoagglutinin that keeps the cells clumped. Washing the cells with saline warmed to 37 °C usually removes it; if not, the cells can be treated with DTT to disperse the IgM. The DAT is then repeated with its control.
- A: An eluate is not useful until the DAT itself is valid.
- C: Polyspecific AHG would be just as invalid with a positive control.
- D: Results cannot be reported while the control is positive.
Question 4 · Medium
AHG reagents for the DAT contain anti-C3d rather than relying on anti-C3b alone. Why?
1. AAnti-C3b would also react with IgG on the cells
2. BC3b on circulating cells is soon cut down to C3d
3. CC3d is the first complement fragment to bind
4. DC3d activates the membrane attack complex
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Answer: B · C3b on circulating cells is soon cut down to C3d
When complement is activated on red cells in the body, factor I quickly breaks C3b down to iC3b and then to C3dg (C3d), which stays on the membrane. Cells that survive in the circulation therefore carry mainly C3d. Anti-C3d detects these cells reliably, which is why polyspecific and monospecific reagents include it. C3d does not lead to further complement activation or rapid clearance.
- A: Anti-C3b reacts with complement, not with IgG.
- C: C1q binds first; C3 fragments come later in the pathway.
- D: C3d does not activate later components; C5b starts the membrane attack complex.
Question 5 · Hard
A new staff member incubates a saline IAT, with no enhancement medium, for 10 minutes, the time used for the LISS method. Why could a weak antibody be missed?
1. ASaline destroys IgG during short incubations
2. BAHG reacts only with LISS-sensitized cells
3. CSaline tests need 30 to 60 minutes for binding
4. DTen minutes is so long that the IgG dissociates
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Answer: C · Saline tests need 30 to 60 minutes for binding
In normal ionic strength saline, antibody uptake is slow, so methods state 30 to 60 minutes at 37 °C for adequate binding. LISS lowers the ionic strength, which speeds antibody uptake and allows 10 to 15 minutes. A shortened saline incubation leaves weak antibodies, such as some Kidd or Duffy antibodies, below the level AHG can detect. Incubation times must follow the method in use and be part of staff training.
- A: Saline does not destroy IgG; it simply allows slower binding.
- B: AHG binds IgG on cells whatever medium was used for sensitization.
- D: Dissociation is a risk when reading is delayed after AHG, not during a short incubation.
Question 6 · Hard
A patient's red cells give a 2+ reaction with an IgG anti-Fya reagent that needs the antiglobulin phase. The DAT is 2+ with anti-IgG. How should the Fy(a+) result be handled?
1. AAccept it if the reaction is stronger than the DAT
2. BTreat it as invalid; coated cells react with AHG anyway
3. CAccept it, because the antiserum is specific
4. DAccept it if IgG-coated check cells then agglutinate
Answer and explanation in LearnFree account
Question 7 · Easy
Which routine blood bank test uses the indirect antiglobulin technique?
1. AThe DAT on a cord sample
2. BThe immediate-spin crossmatch
3. CForward ABO grouping
4. DThe antibody screen
Answer and explanation in LearnFree account
Question 8 · Medium
In a tube antiglobulin test, the tubes stand for 30 minutes after AHG is added before they are centrifuged and read. The likely effect is:
1. AFalsely positive reactions from complement
2. BWeaker or falsely negative reactions
3. CStronger reactions from longer AHG contact
4. DNo effect, as AHG binding is permanent
Answer and explanation in LearnFree account
Question 9 · Medium
A tube IAT is set up with a 10% red cell suspension instead of the 2% to 5% the method states. What is the likely effect?
1. AToo little antibody per cell, so weak reactions
2. BHemolysis in every tube, so invalid results
3. CRouleaux, so false-positive reactions
4. DMore antigen sites, so stronger reactions
Answer and explanation in LearnFree account
Question 10 · Medium
In an indirect antiglobulin test, what happens during the 37 °C incubation?
1. AIgM antibodies are inactivated by heat
2. BAHG cross-links the antibody-coated red cells
3. CAntibody binds to antigens on the red cells
4. DUnbound globulins are washed away
Answer and explanation in LearnFree account
Question 11 · Hard
A patient with a known anti-Jka has a negative anti-IgG gel screen using EDTA plasma. The same day, the patient's serum gives 1+ reactions with Jk(a+) cells in a tube test with polyspecific AHG. The best explanation is that the antibody:
1. AIs detected mainly by the C3 it binds
2. BIs destroyed by EDTA in the sample
3. CHas fallen below a detectable level
4. DReacts only with ficin-treated red cells
Answer and explanation in LearnFree account
Question 12 · Easy
A patient's washed red cells are tested with AHG straight away, with no incubation step. A positive result in this direct antiglobulin test shows:
1. AABO antibodies in the patient's plasma
2. BIgG or complement bound to the cells in the body
3. CAntibody bound to reagent cells at 37 °C
4. DFree antibody present in the patient's plasma
Answer and explanation in LearnFree account
Question 13 · Hard
At 14:00 a laboratory runs a batch of 12 tube antibody screens by the LISS antiglobulin method, washing the cells four times on an automated cell washer before adding anti-IgG. Every tube is negative. IgG-coated check cells are then added to each tube, and none of the 12 agglutinates. The weak anti-D control serum in the same batch also gives 0 with the D-positive screening cell. A drop of the same anti-IgG vial added to check cells in a clean tube gives 3+. The washer's saline reservoir is then found almost empty, with air in the dispensing line. How should the batch be handled?
1. AReport the negative screens as valid
2. BAdd fresh anti-IgG to each tube and reread
3. CRepeat all 12 tests once the washer is repaired
4. DOpen a new anti-IgG vial and repeat the batch
Answer and explanation in LearnFree account
Question 14 · Medium
A 71-year-old woman has anemia with a raised reticulocyte count. Her DAT gel card is shown, and an eluate from her red cells is nonreactive with panel cells. The findings fit best with:
Figure: MedExams
1. ADelayed hemolytic transfusion reaction
2. BPenicillin-induced immune hemolysis
3. CCold agglutinin disease
4. DWarm autoimmune hemolytic anemia
Answer and explanation in LearnFree account

Antiglobulin tests

A patient with myeloma has stacked-coin clumps at immediate spin and 37 °C with all screening cells and the autocontrol, and they disperse when saline is added. Why can the antiglobulin phase of the same tubes still be read reliably?

In a gel IAT, serum spun before it had fully clotted gives a thin line of cells at the top of the gel in every well, including the autocontrol, with most cells at the bottom. The most likely cause is:

DAT results on a patient sample: anti-IgG 2+, anti-C3d 2+, saline control 2+. What should be done next?

AHG reagents for the DAT contain anti-C3d rather than relying on anti-C3b alone. Why?

A new staff member incubates a saline IAT, with no enhancement medium, for 10 minutes, the time used for the LISS method. Why could a weak antibody be missed?

A patient's red cells give a 2+ reaction with an IgG anti-Fya reagent that needs the antiglobulin phase. The DAT is 2+ with anti-IgG. How should the Fy(a+) result be handled?

Which routine blood bank test uses the indirect antiglobulin technique?

In a tube antiglobulin test, the tubes stand for 30 minutes after AHG is added before they are centrifuged and read. The likely effect is:

A tube IAT is set up with a 10% red cell suspension instead of the 2% to 5% the method states. What is the likely effect?

In an indirect antiglobulin test, what happens during the 37 °C incubation?

A patient with a known anti-Jka has a negative anti-IgG gel screen using EDTA plasma. The same day, the patient's serum gives 1+ reactions with Jk(a+) cells in a tube test with polyspecific AHG. The best explanation is that the antibody:

A patient's washed red cells are tested with AHG straight away, with no incubation step. A positive result in this direct antiglobulin test shows:

A 71-year-old woman has anemia with a raised reticulocyte count. Her DAT gel card is shown, and an eluate from her red cells is nonreactive with panel cells. The findings fit best with: