A patient's DAT is positive with polyspecific AHG. What is the next step in the workup?

Test with anti-IgG and anti-C3, and review history

Repeat the DAT with polyspecific reagent only

Report autoimmune hemolytic anemia

Transfuse washed red cells to the patient

A patient on high-dose piperacillin has a positive DAT (IgG and C3) and mild hemolysis. The eluate does not react with any panel cells. What is the next step?

Test the eluate and plasma with drug-treated cells

Repeat the eluate and stop if it is negative

Do a cold autoadsorption on the plasma

Seven days after a red cell transfusion, a patient's DAT is positive (IgG), but the antibody screen is negative. An eluate reacts with Fy(a+) cells only. What explains this?

New anti-Fya is all bound to transfused Fy(a+) cells

The patient has a warm autoantibody to Fya

The eluate was contaminated by plasma antibody

Anti-Fya was passively given in a unit of donor plasma

A D-positive newborn whose D-negative mother received Rh immune globulin at 28 weeks has a weakly positive DAT (IgG) and no hemolysis. The most likely cause is:

Passive anti-D from the antenatal dose

Maternal anti-K missed by the screen

A warm autoantibody in the newborn

A 72-year-old man has a type and screen before elective hip replacement. He has never been transfused and has no transplant history. The PEG antibody screen is negative, but the autocontrol is 1+ at the antiglobulin phase. The DAT is 1+ with anti-IgG and negative with anti-C3d. Hemoglobin 14.1 g/dL (141 g/L), reticulocytes 1.1%, total bilirubin 0.7 mg/dL (12 µmol/L), LD normal, haptoglobin 120 mg/dL (1.2 g/L). He takes amlodipine and metformin and has not received IVIG. Following AABB Technical Manual guidance, the most appropriate action is:

No elution; complete routine compatibility testing

Delay surgery until the DAT becomes negative

Prepare an acid eluate and test it against a panel

Adsorb the plasma before selecting units

Routine tests: direct antiglobulin test

8 ASCP MLS practice questions on Routine tests: direct antiglobulin test, part of Blood Banking. The first 8 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 · Medium
A patient's DAT is positive with polyspecific AHG. What is the next step in the workup?
1. ARepeat the DAT with polyspecific reagent only
2. BTest with anti-IgG and anti-C3, and review history
3. CReport autoimmune hemolytic anemia
4. DTransfuse washed red cells to the patient
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Answer: B · Test with anti-IgG and anti-C3, and review history
Monospecific anti-IgG and anti-C3 show what is coating the cells, which points to the cause. The history matters: recent transfusion, drugs, IVIG, pregnancy and signs of hemolysis. An eluate is made if IgG is present and the patient was recently transfused or is hemolyzing. Many hospital patients have a positive DAT without hemolysis.
- A: Repeating the same test adds no information.
- C: A positive DAT alone does not prove autoimmune hemolysis.
- D: Washing red cells does not address the cause of the positive DAT.
Question 2 · Hard
A patient on high-dose piperacillin has a positive DAT (IgG and C3) and mild hemolysis. The eluate does not react with any panel cells. What is the next step?
1. AReport a warm autoantibody
2. BRepeat the eluate and stop if it is negative
3. CDo a cold autoadsorption on the plasma
4. DTest the eluate and plasma with drug-treated cells
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Answer: D · Test the eluate and plasma with drug-treated cells
A nonreactive eluate in a patient on a drug linked to immune hemolysis suggests a drug-dependent antibody. Testing the plasma and eluate against drug-treated cells, or with the drug added to the test, can confirm it. Piperacillin and some cephalosporins are among the drugs most often implicated. Another cause of a nonreactive eluate is passive anti-A or anti-B from group O plasma or platelets, checked with A1 and B cells.
- A: A warm autoantibody would usually make the eluate react with all cells.
- B: A negative eluate needs explaining, not just repeating.
- C: Cold autoadsorption removes cold autoantibodies, which does not explain this finding.
Question 3 · Hard
Seven days after a red cell transfusion, a patient's DAT is positive (IgG), but the antibody screen is negative. An eluate reacts with Fy(a+) cells only. What explains this?
1. AThe patient has a warm autoantibody to Fya
2. BThe eluate was contaminated by plasma antibody
3. CNew anti-Fya is all bound to transfused Fy(a+) cells
4. DAnti-Fya was passively given in a unit of donor plasma
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Answer: C · New anti-Fya is all bound to transfused Fy(a+) cells
Early in an anamnestic response, all the new antibody may be bound to the transfused antigen-positive cells, leaving none free in the plasma. An eluate concentrates the bound antibody and identifies it before the screen turns positive. This is a delayed serologic or hemolytic transfusion reaction, and Fy(a-) units are needed from now on. The patient's hemoglobin and bilirubin are checked for hemolysis.
- A: An autoantibody would react with the patient's own cells and with every eluate test cell, not only Fy(a+).
- B: A contaminated eluate would show plasma antibody, but the plasma has none.
- D: No plasma was given, and passive antibody would also appear in the plasma screen.
Question 4 · Medium
A D-positive newborn whose D-negative mother received Rh immune globulin at 28 weeks has a weakly positive DAT (IgG) and no hemolysis. The most likely cause is:
1. AMaternal anti-K missed by the screen
2. BABO hemolytic disease
3. CA warm autoantibody in the newborn
4. DPassive anti-D from the antenatal dose
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Answer: D · Passive anti-D from the antenatal dose
Antenatal Rh immune globulin crosses the placenta in small amounts and can coat a D-positive baby's red cells. This gives a weak positive DAT, an eluate with anti-D, and usually no clinically important hemolysis. The baby still has the usual bilirubin checks. The mother remains a candidate for postpartum Rh immune globulin.
- A: Anti-K would be detected by the mother's screen, which includes K-positive cells.
- B: Possible in some pairs, but the antenatal Rh immune globulin points to passive anti-D.
- C: Newborns rarely make red cell autoantibodies.
Question 5 · Hard
A 72-year-old man has a type and screen before elective hip replacement. He has never been transfused and has no transplant history. The PEG antibody screen is negative, but the autocontrol is 1+ at the antiglobulin phase. The DAT is 1+ with anti-IgG and negative with anti-C3d. Hemoglobin 14.1 g/dL (141 g/L), reticulocytes 1.1%, total bilirubin 0.7 mg/dL (12 µmol/L), LD normal, haptoglobin 120 mg/dL (1.2 g/L). He takes amlodipine and metformin and has not received IVIG. Following AABB Technical Manual guidance, the most appropriate action is:
1. ANo elution; complete routine compatibility testing
2. BDelay surgery until the DAT becomes negative
3. CPrepare an acid eluate and test it against a panel
4. DAdsorb the plasma before selecting units
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Answer: A · No elution; complete routine compatibility testing
A positive DAT alone does not mean hemolysis; a weak IgG DAT is found in some healthy blood donors and in many hospital patients. AABB guidance asks whether there is hemolysis, transfusion in the past 3 months, a drug or IVIG cause, or a transplant, and here all of these are absent, with a normal hemoglobin, reticulocyte count, bilirubin, LD and haptoglobin. With no recent transfusion, an eluate cannot reveal an alloantibody against donor cells, so it adds nothing. The plasma screen is negative, so there is nothing to adsorb, and the DAT is no reason to delay surgery. The finding is recorded, and a full workup is done if he is transfused and later shows hemolysis.
- B: A positive DAT without hemolysis is not a reason to delay surgery.
- C: An eluate is useful after recent transfusion or with hemolysis, and neither is present.
- D: The plasma screen is negative, so there is no antibody to remove.
Question 6 · Medium
A 68-year-old woman's EDTA sample, left at room temperature for several hours, gives the DAT results shown. What should be done next?
Figure: MedExams
1. ARepeat the test with polyspecific AHG only
2. BPrepare an eluate from the cells
3. CWash the cells with warm saline and repeat
4. DReport IgG and C3d coating
Answer and explanation in LearnFree account
Question 7 · Easy
Refer to the DAT results shown. The patient's red cells are coated with:
Figure: MedExams
1. ANo IgG or complement
2. BComplement (C3d) only
3. CIgG and complement
4. DIgG only, no complement
Answer and explanation in LearnFree account
Question 8 · Easy
A jaundiced newborn's mother has anti-c. Which test on the baby's red cells shows that they are coated with the maternal antibody?
1. AAntibody screen (indirect antiglobulin test)
2. BReverse ABO grouping
3. CDirect antiglobulin test
4. DWeak D test
Answer and explanation in LearnFree account

Routine tests: direct antiglobulin test

A patient's DAT is positive with polyspecific AHG. What is the next step in the workup?

A patient on high-dose piperacillin has a positive DAT (IgG and C3) and mild hemolysis. The eluate does not react with any panel cells. What is the next step?

Seven days after a red cell transfusion, a patient's DAT is positive (IgG), but the antibody screen is negative. An eluate reacts with Fy(a+) cells only. What explains this?

A D-positive newborn whose D-negative mother received Rh immune globulin at 28 weeks has a weakly positive DAT (IgG) and no hemolysis. The most likely cause is:

A 68-year-old woman's EDTA sample, left at room temperature for several hours, gives the DAT results shown. What should be done next?

Refer to the DAT results shown. The patient's red cells are coated with:

A jaundiced newborn's mother has anti-c. Which test on the baby's red cells shows that they are coated with the maternal antibody?