MLT GlobeDOH exam preparation (Abu Dhabi) – page 3
700 practice MCQs for the DOH medical laboratory exam. Level: Basic to intermediate.
Sodium fluoride in grey-top tubes stops glucose falling in stored blood. Which glycolytic enzyme does fluoride block?
Fluoride, with phosphate and Mg2+, inhibits enolase and so halts glycolysis in the tube. The block is not immediate, so glucose may still fall in the first hour.
A malnourished man with chronic alcohol use has confusion, ataxia and ophthalmoplegia. Which vitamin should be replaced urgently?
This triad is Wernicke encephalopathy, caused by thiamine deficiency. Niacin deficiency causes pellagra (dermatitis, diarrhoea, dementia).
Transamination, decarboxylation and many other amino acid reactions share one vitamin-derived cofactor. Which vitamin is it?
Pyridoxal phosphate forms a Schiff base with amino acids and supports transamination, decarboxylation, deamination and racemisation. B12 is used in only two human enzymes.
Which finding is NOT expected in scurvy?
Vitamin C deficiency weakens collagen, causing bleeding gums, bruising, loose teeth and poor healing. Liver failure is not a feature.
A patient who drinks a lot of carrot juice has yellow-orange palms, but the sclerae are white and bilirubin is normal. What is the cause?
Excess beta-carotene deposits in skin (carotenodermia) and spares the sclera. It is harmless because conversion to retinol is regulated, so it does not cause vitamin A toxicity.
Which situation is LEAST likely to cause a rapid functional vitamin K deficiency?
Citrus fruit supplies vitamin C, not vitamin K. Antibiotics reduce bacterial menaquinone, neonates have low stores, and warfarin blocks vitamin K epoxide reductase.
After lipoprotein lipase removes most of their triglyceride, chylomicron remnants are cleared by which organ?
Hepatocytes take up remnants through apoE binding the LDL receptor and LRP1. Defective apoE (E2/E2) leads to remnant accumulation in type III hyperlipoproteinaemia.
Exposing some foods, such as mushrooms or milk, to ultraviolet light raises their content of which vitamin?
UV-B converts sterol precursors (ergosterol, 7-dehydrocholesterol) to vitamin D2 or D3. This is the basis of UV-treated vitamin D-enriched foods.
A lipaemic sample has a creamy top layer after standing overnight at 4 °C. Which lipid makes up most of this lipoprotein?
The floating layer is chylomicrons, which are about 85–90% dietary triglyceride. They are the least dense lipoproteins.
Which protein, secreted by gastric parietal cells, is needed for vitamin B12 to be absorbed in the terminal ileum?
The intrinsic factor–B12 complex binds cubilin receptors in the ileum. Lack of intrinsic factor, as in autoimmune gastritis, causes pernicious anaemia.
As the respiratory chain pumps protons into the intermembrane space, what happens as they flow back through ATP synthase?
The proton-motive force drives protons back through F0F1 ATP synthase, which phosphorylates ADP. This is Mitchell's chemiosmotic coupling.
On a Wright-stained film, how many nuclear lobes does a normal mature segmented neutrophil usually have?
Mature neutrophils typically show 2–5 lobes joined by thin filaments. Six or more lobes (hypersegmentation) suggests megaloblastic anemia; a bilobed spectacle shape suggests Pelger–Huët anomaly.
During a 100-cell differential on a healthy adult, which leukocyte is the least frequently encountered?
Basophils make up only about 0–1% of circulating leukocytes, so a normal differential may show none. Neutrophils and lymphocytes are the most common.
A heparinized syringe is the standard collection device for which specimen?
Blood gas samples are drawn arterially into syringes containing dry balanced heparin, which does not alter pH or ions. CBCs use EDTA and serum requires clotting.
A patient's serology shows specific antibodies of only one class early in a new infection. Which class is it?
IgM is the first antibody made in a primary immune response, so specific IgM indicates recent or current infection. IgG rises later and persists.
A marrow aspirate is needed from a 20-year-old adult. Which site is preferred?
In adults, red marrow persists mainly in the axial skeleton and proximal long bones; the posterior superior iliac crest is safe and cellular. The tibia is used only in infants.
Before Romanowsky staining, a thin blood film should be fixed with which reagent?
Methanol fixes cells without lysing them. Water-based or acidic reagents such as acetic acid would lyse red cells; acid alcohol is a decolorizer.
Which leukocyte releases major basic protein to attack helminth larvae too large to be phagocytosed?
Eosinophils attach to antibody-coated helminths and release toxic granule proteins such as major basic protein and eosinophil cationic protein.
Which hemoglobin makes up about 95–98% of total hemoglobin in a healthy adult?
HbA (α2β2) predominates in adults, with small amounts of HbA2 (<3.5%) and HbF (<1%). HbS and HbC are abnormal variants.
Which inherited anemia is caused by reduced globin chain synthesis rather than a red cell membrane defect?
Thalassemias are quantitative globin disorders. Spherocytosis, elliptocytosis and stomatocytosis stem from defects in membrane or cytoskeletal proteins or membrane permeability.