MLT GlobeASCP exam preparation (USA · MLS / MLT) – page 34
1200 practice MCQs for the ASCP medical laboratory exam. Level: Advanced.
For pretransfusion antibody screening of a 3-week-old infant, which sample may be used?
Antibodies in young infants are maternal, so either the infant's or the mother's plasma can be used for the initial screen.
A patient has anti-Lea that reacts at room temperature but not at 37 °C or AHG. Which red cells are acceptable?
Lewis antibodies inactive at 37 °C are not clinically significant; antigen-negative units are not required, only AHG-compatible ones.
Why do column (gel) IAT tests not need a cell washing step?
During centrifugation, red cells enter the gel containing AHG, while plasma stays above, so unbound IgG cannot neutralize the AHG.
Why are conventional platelet units NOT stored in the refrigerator?
Chilling changes platelet GPIb, and these platelets are quickly removed by liver macrophages, so their survival is short. Bacteria actually grow better at room temperature, not in the cold.
Replacing most of the plasma in an apheresis platelet unit with platelet additive solution (PAS) mainly reduces:
PAS lowers the plasma volume, so there are fewer plasma proteins causing allergic reactions and less isoagglutinin in ABO-mismatched transfusions. It does not affect lymphocytes (TA-GVHD) or HLA antigens.
A technologist holds a platelet unit to the light and gently presses it. A shimmering, cloudy swirling pattern is seen. This finding indicates:
The 'swirling' effect is due to light scattering by discoid platelets and is a sign of good viability. Loss of swirling suggests platelets have become spherical, often from a fall in pH.
A single unit of cryoprecipitate is thawed and NOT pooled. It is kept at 20–24 °C. It must be transfused within:
Thawed single (or closed-system pooled) cryoprecipitate expires 6 hours after thawing at room temperature. The 4-hour limit applies when pooling is done in an open system.
Plasma labeled as Fresh Frozen Plasma (CPD anticoagulant, standard processing) must be placed in the freezer within what time after collection?
FFP is frozen within 8 hours of collection (or as approved for the collection system). Plasma frozen within 24 hours is labeled PF24 and has slightly lower factor VIII.
Solvent/detergent (S/D) treatment of pooled plasma does NOT reliably inactivate which virus?
Solvent/detergent disrupts lipid envelopes, so it kills enveloped viruses like HIV, HBV and HCV. Non-enveloped viruses such as parvovirus B19 and hepatitis A virus resist this treatment.
Why can 5% albumin be infused without ABO matching and with almost no risk of viral transmission?
Albumin is pasteurized at 60 °C for 10 hours, which inactivates viruses, and the fractionation process removes isoagglutinins. Irradiation and leukofiltration do not remove viruses.
A blood bank refrigerator has an audible alarm. The alarm must be set to activate:
The alarm must sound early enough for staff to act before stored red cells go outside 1–6 °C. It must detect both high and low temperatures.
An FFP unit from a female donor has a green tint. Other inspection is normal. The most likely cause is:
Estrogen raises ceruloplasmin, a copper protein that can give plasma a green colour. Hemolysis gives a red or pink colour, and lipemia gives a milky appearance.
Plasma separated from a whole blood donation and shipped for fractionation into plasma derivatives, rather than transfusion, is called:
Recovered plasma comes from whole blood donations and goes to fractionation. Source plasma is collected by plasmapheresis specifically for fractionation.
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.
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 donor received 2 units of red cells after surgery 10 weeks ago. Under current FDA guidance, the donor:
Receipt of allogeneic blood components leads to a 3-month deferral in current FDA guidance (previously 12 months). At 10 weeks the donor must wait a little longer.
A donor who takes clopidogrel wants to give apheresis platelets. How long after the last dose may platelets be collected?
Clopidogrel irreversibly inhibits platelet ADP receptors, so apheresis platelet donors must wait 14 days. Whole blood donation is still allowed because red cells and plasma are unaffected.
Compared with whole blood donors, donors of two red cell units by apheresis must meet:
Double red cell donation removes about twice the red cell mass, so a higher hematocrit (commonly ≥ 40%) and higher weight/height limits are required.
A D-negative woman received antenatal RhIG at 28 weeks. At delivery, her antibody screen shows anti-D with a titer of 2. The baby is D-positive. What should be done?
A low anti-D titer after antenatal RhIG is usually passive. Unless active immunization is documented, postpartum RhIG should still be given.
A D-negative woman has a spontaneous miscarriage at 9 weeks' gestation. Which RhIG dose may be given?
Before 12 weeks, fetal blood volume is small, so a 50 µg microdose is enough (a 300 µg dose is also acceptable). RhIG prevents anti-D formation after early pregnancy loss.