MLT GlobeMOH exam preparation (UAE) – page 13
700 practice MCQs for the MOH medical laboratory exam. Level: Basic to intermediate.
Haemolytic disease of the fetus and newborn due to Rh incompatibility is which type of hypersensitivity?
Maternal anti-D IgG crosses the placenta and destroys fetal red cells.
Delayed hypersensitivity is characterized by an infiltrate mainly of:
Type IV reactions involve T cells and macrophages, as in the tuberculin test.
Within minutes of an intramuscular penicillin dose, a child develops hypotension, wheeze and airway swelling. Which immune mechanism best explains this?
Onset within minutes with shock and bronchospasm indicates mast-cell degranulation via drug-specific IgE. Serum sickness and Arthus reactions take hours to days to develop.
A healthcare worker has 15 mm of induration 72 hours after an intradermal tuberculin injection. What does this reaction demonstrate?
The tuberculin reaction is delayed-type hypersensitivity showing T-cell memory to M. tuberculosis antigens from infection or BCG. It does not prove active disease.
The 'magic bullet' concept of targeted therapy, delivering a drug or toxin only to cells bearing a chosen antigen, is realised using:
Monoclonal antibodies bind a single epitope and can be conjugated to drugs, toxins or radionuclides, directing them to target cells such as tumours.
A burn patient receives skin taken from his own thigh. What type of graft is this?
Tissue moved from one site to another in the same individual is an autograft; it is genetically identical, so it is not rejected.
An Rh-negative pregnant woman is screened for anti-D, and her newborn's red cells are checked for bound maternal antibody. Which test serves both purposes?
The indirect antiglobulin test detects free anti-D in maternal serum; the direct test detects IgG coating the baby's red cells in haemolytic disease.
Reticulocytes are counted after staining living (unfixed) red cells. Which dye is used for this supravital staining?
New methylene blue (or brilliant cresyl blue) precipitates residual RNA in living reticulocytes. Wright's, Giemsa and Field's are Romanowsky stains used on fixed smears.
Blood for coagulation tests is collected into citrate because the cascade's enzymatic complexes require:
Calcium bridges clotting factors to phospholipid surfaces. Citrate chelates calcium; recalcification restarts clotting in PT/APTT tests.
Which effect is NOT caused by adrenaline?
Through beta-1 receptors adrenaline speeds the heart, through beta-2 it dilates bronchi, and it mobilises glucose. Bradycardia is a vagal (cholinergic) effect.
Which hormone is the main mineralocorticoid, causing sodium retention and potassium loss?
Aldosterone from the zona glomerulosa acts on principal cells of the collecting duct. Cortisol is the main glucocorticoid.
A morning cortisol sample is requested. At what time is plasma cortisol normally highest?
Cortisol peaks soon after waking and is lowest around midnight. Loss of the midnight low (raised late-night salivary cortisol) suggests Cushing syndrome.
Which single test is the most sensitive first-line screen for primary thyroid dysfunction?
Small changes in free T4 cause large log-linear changes in TSH, so TSH becomes abnormal first. Guidelines recommend TSH first, then reflex free T4.
Which condition is LEAST likely to cause hyperthyroidism?
Loss of pituitary TSH causes central (secondary) hypothyroidism. Graves disease, thyroiditis in its release phase and toxic nodules all cause thyrotoxicosis.
Which gland is often called the 'master gland' because its trophic hormones control several other endocrine glands?
The anterior pituitary releases TSH, ACTH, FSH, LH and GH, which regulate the thyroid, adrenals, gonads and liver. It is itself controlled by the hypothalamus.
Which finding would NOT be expected in overt hypothyroidism?
A low metabolic rate causes cold intolerance, weight gain, constipation and bradycardia. Heat intolerance with weight loss suggests hyperthyroidism.
Thyroid tests show high TSH with low free T4 and low free T3. What is the most likely category?
Failure of the thyroid gland (often Hashimoto thyroiditis) lowers FT4/FT3, and feedback raises TSH. Central hypothyroidism gives low or normal TSH.
A patient has central obesity, purple striae, a moon face and hypertension. Excess of which hormone explains this?
These are features of Cushing syndrome, caused by long-term glucocorticoid excess. Aldosterone excess causes hypertension and hypokalaemia without these body changes.
A hypertensive patient has hypokalaemia, suppressed renin and an adrenal adenoma. What is the diagnosis?
Autonomous aldosterone secretion causes sodium retention, potassium loss and renin suppression. Adenomas and bilateral hyperplasia are the common causes.
Overall, what is the most common cause of Cushing syndrome?
Iatrogenic steroid use is the most common cause. Among endogenous causes, pituitary Cushing disease is the most frequent.