MLT GlobeQCHP exam preparation (Qatar) – page 19
749 practice MCQs for the QCHP medical laboratory exam. Level: Intermediate.
The most appropriate specimen for Clostridioides difficile testing is:
Testing formed stool or asymptomatic patients detects colonisation, not disease. Two-step testing (GDH or PCR with a toxin assay) is preferred; test of cure is not recommended.
Which autoantibody is most specific for systemic lupus erythematosus?
ANA is very sensitive for SLE but not specific. Anti-dsDNA and anti-Sm are highly specific, and anti-dsDNA levels follow lupus nephritis activity. Anti-histone suggests drug-induced lupus.
Compared with rheumatoid factor, anti-CCP antibody in rheumatoid arthritis is:
Anti-cyclic citrullinated peptide antibodies are about 95% specific for RA and may appear years before symptoms. RF (IgM against the Fc of IgG) also occurs in infections and other autoimmune diseases.
Saliva from a group A secretor is tested by hemagglutination inhibition. Which soluble substances will it contain?
A secretor of group A secretes A substance plus unconverted H substance. B substance is absent because the person lacks the B transferase.
Which statement best describes the difference between A1 and A2 red cells?
A1 cells carry many more A antigen sites, and the A1 transferase is more efficient. The differences are both quantitative and qualitative. A2 cells have more H, not less.
Which antigen is NOT required on the set of reagent red cells used for antibody screening?
Screening cells must carry D, C, E, c, e, M, N, S, s, P1, Lea, Leb, K, k, Fya, Fyb, Jka and Jkb. Kpa is a low-prevalence antigen and is not required.
A plasma antibody reacts at immediate spin and room temperature with panel cells 2, 5 and 8 but not at AHG. These three cells are the only M+N− cells. The most likely antibody is:
Cold reactivity that follows M antigen and is strongest with homozygous M+N− cells fits anti-M, which shows dosage. Anti-S and anti-Jka usually react at the AHG phase.
All panel cells react 2+ at AHG, the autocontrol and DAT are negative, and the patient was never transfused but had pregnancies. The most likely cause is:
Uniform reactivity with a negative autocontrol points to an alloantibody against an antigen present on almost all cells. Next steps include testing cells lacking high-prevalence antigens and seeking rare donors or siblings.
A panel shows reactions of different strengths at different phases, and no single specificity fits. The best explanation is:
Varied strengths and phases suggest multiple antibodies, each with its own pattern. Selected cells, enzyme-treated cells and antigen typing help separate them.
A patient transfused 5 days ago needs a red cell phenotype. What is the best approach?
Donor cells give mixed-field results. The patient's own reticulocytes, which are less dense, can be separated by microhematocrit centrifugation, or DNA-based typing can be used.
For investigating ABO hemolytic disease of the newborn, which elution method works well?
Heat elution is effective for ABO antibodies, which have relatively low affinity. Chloroquine removes IgG to allow typing and is not an elution method.
During transport, red cell units must be kept at:
AABB allows red cells to be transported at 1–10 °C. The storage range in the refrigerator remains 1–6 °C.
FFP is thawed but not transfused. If kept at 1–6 °C in a closed system and relabeled as Thawed Plasma, it may be used for up to:
Thawed FFP is good for 24 hours as FFP; it can then be relabeled Thawed Plasma and kept at 1–6 °C for up to 5 days total, with lower levels of labile factors V and VIII.
What is the minimum platelet content required in a whole-blood-derived platelet concentrate unit?
Platelets prepared from a single whole-blood unit must contain at least 5.5 × 10^10 platelets. 3.0 × 10^11 is the requirement for an apheresis platelet unit.
In the platelet-rich plasma method, the first centrifugation of whole blood is a:
A light spin leaves platelets in the plasma (PRP). A second heavy spin then concentrates the platelets, and most plasma is removed.
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.
During rapid transfusion of many plasma-rich units, a patient develops perioral tingling and prolonged QT interval. The most likely cause is:
Citrate in the anticoagulant binds ionized calcium, especially when liver clearance is poor. Hypocalcemia causes paresthesia and cardiac changes; calcium is given as treatment.
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.
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 donor took aspirin 24 hours ago. Which statement is correct?
Aspirin irreversibly inhibits platelet cyclooxygenase. Whole blood donation is allowed, but plateletpheresis requires 2 full days after the last dose, and whole-blood platelets should not be the only platelet source.