MLT GlobeMOH exam preparation (UAE) – page 33
700 practice MCQs for the MOH medical laboratory exam. Level: Basic to intermediate.
A glass pipette marked 'TD' is calibrated:
TD (to deliver) pipettes deliver the marked volume when drained; TC (to contain) pipettes hold the marked volume and must be rinsed out.
Which light source is commonly used in spectrophotometers for measurements in the ultraviolet range?
Deuterium lamps give a continuous UV spectrum; tungsten lamps are used for the visible range, and hollow cathode lamps for atomic absorption.
Parvovirus B19 selectively infects erythroid progenitor cells. Which red cell antigen serves as its receptor?
B19 binds P antigen (globoside); rare P-null (p phenotype) individuals are resistant. Duffy antigen is the receptor for Plasmodium vivax.
Rotavirus was long classified in the family Reoviridae. In which family does ICTV now place it?
In 2022 ICTV split Reoviridae; rotaviruses are now in Sedoreoviridae (order Reovirales). Noroviruses are caliciviruses.
Where in the human intestine does Cryptosporidium develop?
Cryptosporidium sits in an intracellular but extracytoplasmic vacuole at the microvillous surface of enterocytes, mainly in the small intestine.
Parasite products released at schizont rupture trigger fever mainly by stimulating which host cytokine?
Glycosylphosphatidylinositol and hemozoin activate macrophages to release TNF-alpha and IL-1, which act as endogenous pyrogens. IL-4, IL-10 and TGF-beta are mainly anti-inflammatory or Th2 cytokines.
Which tapeworm uses humans only rarely, as an accidental intermediate host with larvae (coenurus) in the brain or eye?
Coenurosis is a rare zoonosis from dog tapeworm T. multiceps eggs. T. saginata, T. solium and H. nana commonly infect humans.
A leishmanin (Montenegro) skin test is typically negative in:
Active kala-azar suppresses cell-mediated immunity, so the delayed-hypersensitivity test is negative; it becomes positive after cure. Cutaneous forms usually give a positive test.
Medium-sized blasts with deep blue, vacuolated cytoplasm and a 'starry-sky' pattern on lymph node biopsy are associated with which translocation?
This is Burkitt lymphoma/leukemia, driven by MYC translocation, most often t(8;14) with IGH. t(14;18) is follicular lymphoma and t(11;14) is mantle cell lymphoma.
Treating panel cells with ficin or papain destroys which antigens?
Proteolytic enzymes cleave Fya, Fyb, M, N and (variably) S. They enhance reactions of Rh, Kidd, Lewis, P1 and I antibodies, which helps separate mixtures in antibody identification.
ABH antigens on the red cell membrane are built mainly on which type of precursor oligosaccharide chain?
Red cell ABH antigens are made mainly on type 2 chains by FUT1. Type 1 chains are used in secretions and plasma (FUT2), which is why Lewis and soluble ABH relate to type 1.
A long-term hemodialysis patient has an anti-N-like antibody reacting with all cells. This is linked to reuse of dialyzers sterilized with:
Formaldehyde alters N-like structures on the patient's red cells, leading to anti-Nf. It usually reacts at room temperature and is of little clinical significance.
An R1R1 patient has anti-c. Which red cell units are most appropriate for transfusion?
R1R1 people lack c and E, and anti-E often accompanies anti-c or develops later. Giving R1R1 (c−E−) units prevents both. C-negative units would be c-positive.
A patient in DKA improves with treatment, yet the nitroprusside ketone test becomes more strongly positive. The best explanation is:
In DKA most ketone is beta-hydroxybutyrate, which nitroprusside does not detect. With treatment it is oxidised to acetoacetate, so the test rises. Measuring beta-hydroxybutyrate avoids this problem.
In the ammonium molybdate method for inorganic phosphate, the unreduced phosphomolybdate complex is measured at:
Many automated methods read the unreduced ammonium phosphomolybdate complex in the UV at 340 nm. Reduction to molybdenum blue (read near 600–700 nm) is an older alternative.
Which finding suggests that hyponatremia is due to hypothyroidism or adrenal insufficiency rather than a laboratory artefact?
True hypo-osmolar hyponatremia shows low measured osmolality. Pseudohyponatremia from lipid or protein excess has normal measured osmolality because osmolality depends on plasma water solutes.
A patient has persistently raised serum amylase, normal lipase, and a low amylase-to-creatinine clearance ratio. No abdominal pain. The most likely cause is:
Macroamylase is amylase bound to immunoglobulin; it is too large to be filtered, so serum amylase stays high while urine amylase is low. Lipase is normal and there is no pancreatic disease.
A lipemic plasma left overnight at 4 °C shows a creamy top layer over a turbid lower layer. Which lipoproteins are increased?
The creamy layer is chylomicrons and the turbid infranate is VLDL, the pattern of type V hyperlipoproteinemia. Chylomicrons alone leave a clear infranate.
A 65-year-old with bone pain and renal failure has low gamma globulin and no visible spike on serum electrophoresis. Which tests best detect a light-chain-only myeloma?
Free light chains are small, cleared by the kidney and often invisible on serum electrophoresis, which may show only reduced gamma. Serum free light chain assay and urine immunofixation are the sensitive tests.
Which pattern best suggests post-renal azotemia from bilateral ureteral obstruction early in its course?
Early obstruction increases urea back-diffusion, so the ratio is usually raised as in prerenal states. A low ratio with casts suggests intrinsic renal injury such as acute tubular necrosis.