MLT GlobeBlood Banking: Crossmatch & compatibility – page 2
51 Blood Banking MCQs on Crossmatch & compatibility with answers and explanations.
During a transfusion, the patient must be watched most closely during the first:
Severe reactions such as acute hemolysis and anaphylaxis usually start early, so vital signs are checked and the patient observed closely in the first 15 minutes.
A group A, D-positive patient can receive red cells of which groups?
The patient's plasma has anti-B, so red cells must lack B (group A or O). Being D-positive, the patient can receive D-positive or D-negative cells.
In a tube crossmatch, the phase that detects IgG antibodies coating donor red cells requires:
IgG antibodies sensitize cells without agglutinating them in saline; after 37 °C incubation, AHG bridges the coated cells. The immediate-spin saline phase detects ABO incompatibility.
A group AB patient needs red cells, but no AB units are available. What is the next preferred choice?
AB patients can receive A or B red cells (A is more available), then O. Whole blood of other groups carries plasma anti-A or anti-B against the patient's cells.
An immediate-spin crossmatch is mainly designed to detect:
Immediate-spin (room temperature) crossmatching confirms ABO compatibility when the antibody screen is negative. Clinically significant IgG antibodies need an antiglobulin (AHG) crossmatch.
Which condition must be met before a laboratory may use an electronic (computer) crossmatch?
The computer crossmatch requires a validated system, no clinically significant antibodies, and at least two ABO determinations with one on the current sample. A negative DAT is not a requirement.
A routine major crossmatch will usually NOT detect:
A D-negative patient without anti-D gives a compatible crossmatch with D-positive cells, so D typing errors are missed. ABO mismatch, antibodies to donor antigens and a donor positive DAT can all give incompatibility.
All AHG crossmatches are incompatible, all screening cells react at AHG, and the autocontrol and DAT are positive with IgG. The most likely explanation is:
Panreactivity together with a positive autocontrol and IgG DAT points to a warm autoantibody. An alloantibody to a high-frequency antigen gives a negative autocontrol in a non-transfused patient.
What is the main risk of giving large volumes of group O apheresis platelets to a group A child?
Group O platelet plasma may contain high-titer anti-A that can lyse the child's red cells. Many services limit incompatible plasma volume or use titer-screened units.
Modern massive transfusion protocols for trauma aim to give red cells, plasma and platelets in which approximate ratio?
Balanced resuscitation with near 1:1:1 ratios of red cells, plasma and platelets reduces dilutional coagulopathy compared with red cells plus crystalloid.
During a D-negative inventory shortage, which patient is the most suitable to switch to D-positive red cells?
Switching is acceptable for males and women beyond childbearing age without anti-D, because anti-D formation then has little consequence for HDFN. Patients with anti-D must receive D-negative red cells.
A patient with multiple myeloma shows agglutination in all immediate-spin crossmatches that looks like stacked coins. The best way to confirm rouleaux is:
Rouleaux disperses when the plasma is removed and replaced with saline, while true agglutination remains. It is caused by abnormal plasma proteins, not antibodies.
For adult patients, which component is usually issued without regard to ABO compatibility?
Cryoprecipitate has very little plasma per unit, so ABO antibodies are negligible in adults. Granulocytes contain many red cells and must be ABO-compatible.
Why must granulocyte concentrates be ABO-compatible and crossmatched with the recipient?
Granulocyte concentrates contain significant red cell contamination (often >2 mL), so a crossmatch is required to prevent hemolysis.
A surgical service crossmatched 300 units in one month and transfused 90. What does this indicate?
C:T ratio = 300 ÷ 90 ≈ 3.3. A ratio above about 2.0 suggests too many crossmatches; a maximum surgical blood order schedule or type-and-screen helps.
A patient's ABO group today is A, but a record from last year shows group O. Both samples were labeled correctly. The most likely problem is:
A clear change from group O to group A suggests a sample was drawn from the wrong patient (WBIT). Comparing results with historical records is required to detect this error; a new sample should be collected.
A crossmatch uses EDTA plasma. Why might a hemolysing antibody such as anti-Jka show agglutination but no hemolysis?
Complement activation needs Ca2+ and Mg2+, which EDTA binds. So in vitro hemolysis is seen only in serum; with EDTA plasma the antibody is detected by agglutination at AHG.
An adult male trauma patient of unknown blood group needs red cells before any testing. The preferred uncrossmatched units are:
Group O D-positive red cells are commonly used for adult males to save scarce D-negative units. Group O D-negative is reserved for girls and women of childbearing potential.
In a tube crossmatch at the AHG phase, the tube shows a clear red supernatant with few red cells remaining. How should this be interpreted?
Hemolysis means an antibody bound and activated complement to lyse the cells; it is a positive reaction. This is seen with antibodies such as anti-Jka or anti-Vel in serum samples.
A patient has an ABO discrepancy that cannot be resolved before urgent transfusion. Which components should be given?
Until the ABO group is resolved, give red cells that lack A and B (group O) and plasma that lacks anti-A and anti-B (group AB). This is safe whatever the true group.