MLT GlobeDHA exam preparation (Dubai) – page 21
700 practice MCQs for the DHA medical laboratory exam. Level: Basic to intermediate.
A woman with heavy periods and easy bruising has a prolonged PFA-100 closure time and low ristocetin cofactor activity. The most likely diagnosis is:
von Willebrand factor links platelets to damaged vessel walls and carries factor VIII. Its deficiency causes mucosal bleeding, poor platelet adhesion and low ristocetin cofactor activity; aPTT may be mildly prolonged.
Most neutrophils of a healthy person have round bilobed ('pince-nez') nuclei with normal granules. Family members show the same. This is:
Pelger-Huët anomaly is a harmless inherited defect (lamin B receptor) with hyposegmented but normally functioning neutrophils. The acquired look-alike (pseudo-Pelger) occurs in MDS.
An E. coli resistant to ceftazidime and cefotaxime shows a much larger zone when clavulanic acid is added to the disk. This indicates:
ESBLs break down third-generation cephalosporins but are inhibited by clavulanate, so the combination disk zone grows (about 5 mm or more). AmpC enzymes are not inhibited by clavulanate.
Anaphylaxis during transfusion in a patient with IgA deficiency and anti-IgA is best prevented in future by giving:
The reaction is caused by the patient's anti-IgA binding donor plasma IgA. Washing removes plasma; plasma products must come from IgA-deficient donors. Irradiation and leukoreduction do not help.
pH 7.25, pCO2 60 mmHg, HCO3 26 mmol/L. This is:
Low pH with high pCO2 means respiratory acidosis. Bicarbonate is still near normal, so renal compensation has not yet happened: an acute process such as hypoventilation.
A large air bubble left in an arterial blood gas syringe will most likely cause:
Gases equilibrate with room air, which has high O2 (about 150 mmHg) and almost no CO2. Losing CO2 also raises the pH. Bubbles must be expelled and the syringe capped at once.
Narrow, septate hyphae with regular acute-angle (about 45°) branching in lung tissue suggest:
Aspergillus has narrow septate hyphae branching at acute angles. Mucorales have broad, ribbon-like, mostly aseptate hyphae with right-angle branching, which changes treatment.
A group A patient needs fresh frozen plasma. Which plasma groups are compatible?
Plasma must not contain antibody against the recipient's antigens. Group A plasma (anti-B) and AB plasma (no antibody) are safe; group O plasma contains anti-A.
Parents with genotypes AO and BO have a child. Which child phenotypes are possible?
Each parent can pass A or O, and B or O. Combinations give AB, AO (A), BO (B) and OO (O), so all four phenotypes are possible.
In a solid-phase red cell adherence antibody screen, a positive reaction looks like:
When antibody is present, indicator cells bind across the coated well and form a carpet. With no antibody, indicator cells roll down and form a small button.
Plasma is treated with dithiothreitol (DTT), and an antibody's reactivity disappears. This shows the antibody is mainly:
DTT breaks the disulfide bonds joining IgM subunits, destroying its agglutinating ability, while IgG stays reactive. This helps judge whether an antibody could cross the placenta.
Under AABB standards, a leukocyte-reduced red cell unit must contain fewer than:
AABB requires < 5 × 10^6 WBCs per leukocyte-reduced red cell or apheresis platelet unit (Council of Europe uses < 1 × 10^6).
Plasma cryoprecipitate reduced (cryo-poor plasma) is sometimes used for plasma exchange in TTP because it:
Removing cryoprecipitate removes most fibrinogen, factor VIII and large VWF multimers, while ADAMTS13 remains. This makes it an alternative replacement fluid in TTP.
Granulocyte concentrates should be:
Granulocytes lose function quickly, so they are kept at room temperature without agitation and given as soon as possible, within 24 hours. They must also be irradiated.
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.
In copper sulfate screening, a drop of donor blood sinks in a solution with specific gravity 1.053. This means:
A specific gravity of 1.053 corresponds to hemoglobin of about 12.5 g/dL. A drop that sinks is denser than the solution, so the donor meets the requirement; a floating drop fails.
Preoperative autologous collection should be completed no later than how long before surgery?
The last autologous collection should be at least 72 hours before surgery so the patient's plasma volume can recover. Shorter gaps increase risk of hypovolemia.
A patient with a strongly positive DAT types D-positive with a high-protein anti-D reagent. What control is needed to validate this result?
High-protein reagents can agglutinate IgG-coated cells without true D. An Rh (diluent) control must be negative for the D result to be valid.
An 80-year-old with heart failure becomes breathless during her second red cell unit. BP 180/100 mmHg, distended neck veins, raised NT-proBNP. The most likely reaction is:
Hypertension, raised venous pressure and a high BNP point to volume overload. TRALI typically causes hypotension and a normal BNP, and it is not related to fluid volume.
What is the main mechanism of most TRALI cases?
Donor antibodies to HLA or neutrophil antigens activate recipient neutrophils in lung capillaries, causing leaky vessels. This is why plasma from men or never-pregnant women is preferred.