MLT GlobeDOH exam preparation (Abu Dhabi) – page 23
700 practice MCQs for the DOH medical laboratory exam. Level: Basic to intermediate.
Which result pattern is expected in isolated severe thrombocytopenia?
Low platelets impair primary hemostasis only, so bleeding time lengthens while clotting-factor tests stay normal. Abnormal PT/APTT with low fibrinogen suggests DIC.
Which condition rules out collecting a patient's own blood for later autologous transfusion?
Bacteraemia risks bacterial growth in the stored unit. Pre-deposit weeks ahead, adequate haemoglobin and elective surgery are standard requirements for autologous donation.
A child is blood group A. Which pair of parental ABO groups could NOT have produced this child?
The child needs an A allele from one parent. An O (OO) parent and a B (BO or BB) parent carry no A allele, so a group A child is impossible.
A female donor is being screened. Under AABB criteria, what is the lowest acceptable haematocrit?
AABB requires Hb ≥12.5 g/dL or Hct ≥38% for female donors (≥13.0 g/dL or ≥39% for males) to protect the donor from anaemia.
Which urine finding is a hallmark of an acute intravascular haemolytic transfusion reaction?
Intravascular lysis releases free haemoglobin that saturates haptoglobin and spills into the urine, giving red-brown urine. Unconjugated bilirubin rises in serum but does not appear in urine.
What is the main reason for freezing red cells in glycerol for long-term storage?
Frozen glycerolised RBCs can be kept for 10 years, allowing rare units (and some autologous units) to be stockpiled. They are expensive and slow to prepare, so not for routine use.
About a week after a transfusion, a patient previously pregnant develops falling haemoglobin, jaundice and a positive DAT. This is best explained by:
Re-exposure to an antigen boosts a previously undetectable IgG alloantibody (e.g., Kidd) 3–14 days later, causing extravascular haemolysis. The other reactions occur within hours.
Which condition is typically associated with WARM rather than cold autoimmune haemolytic anaemia?
SLE (and CLL, methyldopa) cause IgG warm AIHA. Mycoplasma (anti-I) and EBV (anti-i) trigger cold IgM autoantibodies; lymphomas can cause either type.
Which donor can be accepted without deferral?
Toxoid and inactivated vaccines need no deferral if the donor is well. Post-exposure rabies vaccination defers for a year; active TB and recent syphilis also defer.
Which vaccine requires a donor deferral of about 4 weeks?
Live attenuated vaccines such as rubella or varicella need about 4 weeks' deferral because of transient viraemia. Killed, toxoid and recombinant vaccines need none if the donor is well.
Which haemostatic problem is the most frequent consequence of massive transfusion with stored red cells and crystalloid?
Stored red cells contain few viable platelets or labile factors, so replacing a blood volume dilutes platelets and clotting factors. Citrate load causes hypocalcaemia, not hypercalcaemia.
Which change speeds up antibody uptake onto red cells in antibody-screening tests?
Low-ionic-strength solution reduces the ion cloud around cells, increasing antibody association and allowing shorter incubation. pH, temperature and time also influence binding.
Which biochemical change is characteristic of refrigerated stored red cells?
Cold inhibits the Na⁺/K⁺-ATPase, so K⁺ moves out and Na⁺ moves in; 2,3-DPG and pH fall with storage.
A jaundiced newborn of a group O, RhD-negative mother is suspected of haemolytic disease. Which test on cord blood shows maternal antibody on the baby's cells?
A positive DAT confirms in-vivo coating of fetal cells by maternal IgG. The Kleihauer test quantifies fetomaternal haemorrhage in the mother.
Which donor can be accepted and does not need deferral?
Recombinant HBV vaccine without known exposure needs no deferral. Uncontrolled seizures, cardiac disease and fever defer to protect donor or recipient.
Which is a valid indication for fresh frozen plasma?
FFP replaces all coagulation factors in bleeding patients with liver disease, DIC or when concentrate is unavailable. ITP needs immunotherapy, not plasma.
In the oliguric phase following a severe haemolytic transfusion reaction, which laboratory pattern is expected?
Acute kidney injury from haemoglobin, hypotension and DIC causes retention of urea, creatinine and potassium.
Which statement about 'incomplete' antibodies is FALSE?
Anti-A and anti-B are mostly IgM and agglutinate saline-suspended cells directly (complete). Incomplete antibodies are IgG, warm-reacting and AHG-dependent.
Red cells of subgroup A2 typically give which pattern?
A2 cells carry fewer A antigen sites and lack the A1 epitope, so Dolichos biflorus lectin does not agglutinate them.
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.