MLT GlobeDOH exam preparation (Abu Dhabi) – page 12
700 practice MCQs for the DOH medical laboratory exam. Level: Basic to intermediate.
Which is the largest purely endocrine gland in an adult?
The thyroid weighs about 15–25 g and wraps around the trachea. The adrenals are about 4–5 g each and the pituitary under 1 g.
Which secretion is released through a duct (exocrine), not into the blood?
Salivary glands empty through ducts into the mouth. Oxytocin, thyroxine and vasopressin are hormones released into the bloodstream.
Thyroid hormones are made by iodinating residues of which amino acid within thyroglobulin?
Thyroid peroxidase iodinates tyrosyl residues to MIT and DIT, which couple to form T3 and T4. Thyroglobulin is also a tumour marker after thyroidectomy.
Calcitonin from thyroid C-cells lowers the blood level of which ion?
Calcitonin inhibits osteoclasts and lowers serum calcium. Clinically it is used as a tumour marker for medullary thyroid carcinoma.
Which estrogen is the main ovarian product in premenopausal women and the one measured to assess follicular function?
Estradiol from growing follicles is monitored during ovarian stimulation. Estriol comes mainly from the fetoplacental unit, and estrone predominates after menopause.
A woman has hirsutism that has progressed quickly. Which hormones are measured first to look for an ovarian or adrenal androgen source?
Very high testosterone suggests an ovarian source and high DHEA-S an adrenal source. Rapid virilisation raises concern for a tumour.
Which glucocorticoid is the main one secreted by the human adrenal cortex?
The zona fasciculata secretes about 10–20 mg of cortisol a day. Corticosterone is the main glucocorticoid in rodents, and aldosterone is a mineralocorticoid.
Why should creatinine be measured on a 24-hour urine sent for VMA or metanephrines?
Creatinine excretion is fairly constant, so a low value suggests under-collection. Specimens are usually acidified with HCl, and interfering drugs should be reviewed.
Rouleaux on the smear, a monoclonal band on serum protein electrophoresis and more than 10% clonal plasma cells in the marrow indicate:
Excess monoclonal immunoglobulin coats red cells and causes rouleaux. A monoclonal (M) protein plus at least 10% clonal marrow plasma cells, with end-organ damage, defines multiple myeloma.
Which plasma group can be given to patients of any ABO group?
Group AB plasma has neither anti-A nor anti-B, so it will not attack any recipient's red cells. For red cells the rule is reversed: group O is the universal donor.
Howell-Jolly bodies are nuclear (DNA) remnants most commonly seen after:
The spleen normally removes these small round DNA fragments from red cells. After splenectomy or in functional asplenia (e.g. sickle cell disease) they stay in circulating cells.
The minimum interval between two whole blood donations by the same donor is:
An interval of 8 weeks (56 days) lets the donor replace iron and red cells. Longer intervals apply after double red cell apheresis (16 weeks).
Out of 100 people with a disease, a test is positive in 90. The test's sensitivity is:
Sensitivity = true positives ÷ (true positives + false negatives) = 90 ÷ 100 = 90%. Specificity would need results from people without the disease.
According to Beer's law, absorbance is directly proportional to:
A = a × b × c: absorbance equals absorptivity × light path × concentration. Transmittance falls logarithmically as concentration rises, so %T is not linear.
The genes that encode the ABO glycosyltransferases are located on which chromosome?
The ABO gene is on chromosome 9q34. Chromosome 1 carries the RH genes, and chromosome 19 carries the H (FUT1), Se (FUT2) and Le (FUT3) genes.
ABO antigens are important in solid organ transplantation mainly because they are:
ABH are histo-blood group antigens found on endothelium and many epithelial cells. ABO-incompatible grafts risk hyperacute rejection from recipient anti-A or anti-B.
In tube ABO typing, a mixed-field reaction looks like:
Mixed field shows agglutinates alongside a large population of unagglutinated cells, indicating two cell populations. Coin-like stacking is rouleaux.
In a column (gel) agglutination test, a strong positive (4+) reaction appears as:
Large agglutinates cannot enter the gel and stay at the top. Unagglutinated cells pass through and form a button at the bottom, which is a negative reaction.
After a panel suggests anti-E, some specificities are still not excluded. The next step is usually to:
Selected cells lacking E but carrying the unexcluded antigens show whether another antibody is hiding. Repeating the same panel gives no new information.
The sensitization step of the indirect antiglobulin test is performed at:
IgG antibodies bind best at body temperature, so plasma and cells are incubated at 37 °C before washing and adding AHG. 56 °C is used for heat elution.