MLT GlobeDHA exam preparation (Dubai) – page 27
700 practice MCQs for the DHA medical laboratory exam. Level: Basic to intermediate.
A patient with severe liver failure has fine, colourless-to-yellow needle crystals in sheaves in an acidic urine. These are most likely:
Tyrosine crystals (needles in clusters or sheaves) and leucine spheres appear in severe liver disease or inherited amino acid disorders. They are abnormal crystals of clinical significance.
Round structures in urine sediment could be red cells or yeast. Which simple step helps distinguish them?
Dilute acetic acid lyses red cells; yeast remain and may show budding or hyphae. Red cells are also more uniform in size and do not bud.
A group A patient received several group O apheresis platelet units. Reverse typing now shows a weak reaction with A1 cells, and the DAT is weakly positive. The most likely cause is:
Group O platelet units contain plasma with anti-A, which can appear in reverse typing and coat the patient's A cells. The patient's forward type was A1-compatible, so anti-A1 production is unlikely.
In ABO forward typing, using a red cell suspension that is much too heavy most likely causes:
Too many red cells relative to antibody (antigen excess) can weaken agglutination and cause false negatives. Rouleaux come from abnormal plasma, not heavy cell suspensions.
Pooled screening cells (red cells from two donors mixed) are acceptable for:
Pooling dilutes each antigen and can miss weak antibodies, so pooled cells are allowed only for donor screening. Patient testing uses unpooled cells.
In a neutralization test, a control of plasma plus saline (instead of the neutralizing substance) is included to show that:
Adding any fluid dilutes the plasma. The saline control must still react; otherwise loss of reactivity may be due to dilution.
A hospital wants to extend the dating of its apheresis platelets from 5 to 7 days. Which measure allows this under current FDA guidance?
Large-volume, delayed sampling culture reduces the risk of bacterial contamination enough to permit 7-day storage. Irradiation and leukoreduction prevent TA-GVHD and leukocyte effects but do not address bacteria.
Under FDA criteria, hemolysis in a red cell unit at the end of its storage period must be less than:
FDA requires end-of-storage hemolysis below 1% (European standards use 0.8%). Higher hemolysis indicates poor red cell quality or damage during processing.
Apheresis platelets are volume-reduced by centrifugation in an open system for a small child. The product must be transfused within:
Volume-reduced platelets prepared in an open system expire 4 hours after processing. Volume reduction is used to limit fluid load or incompatible plasma.
A patient has anti-M that reacts only at room temperature and not at 37 °C or AHG. What red cells should be given?
Anti-M that does not react at 37 °C is not clinically significant, so antigen-negative units are not needed. Crossmatch-compatible units at 37 °C/AHG are acceptable.
A donor had malaria 18 months ago and was successfully treated. What is the correct decision under FDA guidance?
A person diagnosed with malaria is deferred for 3 years after completing treatment and being symptom-free. Semi-immune people may carry low-level parasitemia for a long time.
A male donor takes finasteride for hair loss. Why is he deferred for 1 month after the last dose?
Finasteride is teratogenic; it blocks 5-α-reductase and may affect male fetal genital development. A 1-month deferral lets the drug clear before donation.
Colton antigens are carried on which red cell protein?
The Colton antigens are on the water channel aquaporin-1. The Kidd glycoprotein is a urea transporter.
A never-transfused, never-pregnant man has a weak anti-E found only with enzyme-treated cells. This is best described as:
Anti-E is the Rh antibody most often found without a known stimulus and is often enzyme-only. RhIG contains anti-D, not anti-E.
The DEL phenotype, which types D-negative by routine methods, is most common in people of:
DEL is found in a large share of apparently D-negative East Asians. Most D-negative Europeans have a full RHD deletion instead.
Intravenous anti-D immunoglobulin used to treat immune thrombocytopenia is effective only in patients who are:
Anti-D coats the patient's own D-positive red cells, which then occupy splenic Fc receptors and spare platelets. It has no target in D-negative patients.
Respiratory distress develops within 24 hours of transfusion. It does not meet the criteria for TRALI, TACO or allergic reaction. This is classified as:
TAD is respiratory distress within 24 hours that cannot be explained by TRALI, TACO, allergy or the patient's condition. It is a diagnosis of exclusion in hemovigilance definitions.
Acute respiratory distress develops 2 hours after plasma transfusion. Which finding favours TRALI rather than TACO?
TRALI is non-cardiogenic lung injury and often presents with fever and hypotension. TACO usually shows hypertension, raised natriuretic peptides and responds to diuretics.
An arterial sample in a plastic syringe will be analysed within 20 minutes. Why is placing it in ice water not recommended?
Current guidance is to keep plastic syringes at room temperature and analyse within 30 minutes. Cooling increases gas diffusion through plastic, allowing oxygen entry and falsely high pO2. Cold slows, not increases, glycolysis.
A breastfed 2-week-old with vomiting, jaundice and poor weight gain has a positive copper-reduction urine test but a negative glucose oxidase dipstick. Which enzyme is most likely deficient?
Classic galactosemia (GALT deficiency) causes galactose accumulation after milk feeding. Galactose is a reducing sugar detected by copper reduction but not by the glucose-specific glucose oxidase strip.