MLT GlobeQCHP exam preparation (Qatar) – page 29
749 practice MCQs for the QCHP medical laboratory exam. Level: Intermediate.
A well adult with sickle cell trait is most likely to show which clinical or laboratory feature?
The hypoxic, acidic, hypertonic renal medulla causes sickling even in trait, leading to hyposthenuria and papillary hematuria. Carriers do not have chronic hemolysis, crises or autosplenectomy.
Methylene blue treatment for drug-induced methemoglobinemia may fail and cause hemolysis in patients with:
Methylene blue reduces methemoglobin using NADPH, which G6PD produces. Without enough NADPH it is ineffective and can itself cause oxidant hemolysis.
The leading cause of death in untreated paroxysmal nocturnal hemoglobinuria is:
PNH has a high rate of venous thrombosis in unusual sites such as the hepatic (Budd–Chiari), portal and cerebral veins, which is the major cause of death. Iron is lost in urine rather than overloaded.
The intrinsic tenase complex that activates factor X on phospholipid surfaces is made of:
Factor IXa with its cofactor VIIIa activates factor X very efficiently; this is why deficiency of VIII or IX causes hemophilia. Xa with Va forms the prothrombinase complex.
A man with hemophilia A and a non-carrier wife has children. Which statement about inheritance is correct?
Hemophilia A is X-linked recessive. An affected father passes his X to every daughter (obligate carriers) and his Y to every son, so sons are unaffected.
A patient has prolonged PT and aPTT. Factor V is 95%, and factors II, VII, IX and X are low. The most likely cause is:
Factor V is not vitamin K–dependent, so it stays normal in vitamin K deficiency or warfarin use. In liver disease factor V is also low because the liver makes it.
A heparin-contaminated sample needs aPTT testing. Which agent can be added to neutralize heparin in vitro?
Heparinase enzymatically breaks down heparin (polybrene and protamine also neutralize it) so the underlying clotting time can be seen. Tranexamic acid is an antifibrinolytic.
A term newborn develops purpura fulminans within hours of birth with undetectable protein C activity. The likely cause is:
Severe (homozygous or compound heterozygous) protein C deficiency causes neonatal purpura fulminans with skin necrosis and DIC. NAIT and vitamin K deficiency cause bleeding, not thrombosis.
Most chromogenic coagulation assays measure the release of para-nitroaniline (pNA), read at a wavelength of:
Enzymes such as thrombin or Xa cleave a synthetic peptide–pNA substrate, releasing yellow pNA read at 405 nm. 340 nm is used for NADH-based chemistry reactions.
A patient develops megaloblastic anemia and numb legs after repeated recreational nitrous oxide use. Nitrous oxide causes this by:
Nitrous oxide oxidizes the cobalt of cobalamin, inactivating methionine synthase and causing functional B12 deficiency even with normal serum B12. Dihydrofolate reductase is inhibited by methotrexate, not nitrous oxide.
A patient with undiagnosed vitamin B12 deficiency is treated with folic acid alone. The most likely result is:
Large doses of folic acid can partly correct the megaloblastic anemia, but they do not treat B12-dependent nerve damage, which may worsen. B12 status should be checked before giving folate.
In developing iron deficiency, which CBC parameter often becomes abnormal before the MCV falls below the reference range?
As iron-restricted erythropoiesis starts, a population of smaller cells appears and the RDW rises while the average MCV is still normal. MCHC is usually the last index to fall.
Basophilic stippling on a Wright-stained smear represents aggregated:
Stippling is precipitated ribosomal RNA, seen when ribosome breakdown is impaired, as in lead poisoning. Denatured hemoglobin forms Heinz bodies, iron granules are Pappenheimer bodies and DNA remnants are Howell-Jolly bodies.
Mature trophozoites stretched across normal-sized red cells as bands, and schizonts with about 8 merozoites in a rosette, suggest:
Band-form trophozoites and rosette ('daisy-head') schizonts in normal or small red cells are typical of P. malariae. P. vivax enlarges the red cell and its schizonts have 12–24 merozoites.
In P. falciparum infection, usually only ring forms and gametocytes are seen in peripheral blood because:
Knobs on infected red cells make them adhere to endothelium (sequestration), so mature trophozoites and schizonts stay in deep capillaries. Seeing schizonts in the blood suggests heavy, severe infection.
During an oxidant hemolytic crisis, the smear shows small, dense red cells with irregular outlines and no central pallor. These are best called:
Oxidant damage (as in G6PD deficiency or unstable hemoglobins) forms dense, irregularly shaped contracted cells. They differ from spherocytes by their uneven outline.
Teardrop cells (dacrocytes) are thought to form when red cells:
Cells squeezed through fibrotic marrow or splenic cords may be stretched into a tail and stay deformed. Fibrin strands produce schistocytes, and lipid gain produces target cells or acanthocytes.
In chronic lymphocytic leukemia, which FISH result as the only abnormality predicts the most favorable course?
Isolated del(13q14) is the most common CLL abnormality and is linked to the best outcome. del(17p) (TP53 loss) is the worst, and del(11q) (ATM) is also unfavorable; trisomy 12 is intermediate.
Before therapy for chronic lymphocytic leukemia, testing for TP53 abnormality is important mainly because it:
del(17p)/TP53 mutation predicts resistance to standard chemoimmunotherapy, so these patients receive targeted agents such as BTK or BCL2 inhibitors. It is prognostic and predictive, not diagnostic.
All-trans retinoic acid (ATRA) is effective in acute promyelocytic leukemia because it:
ATRA overcomes the transcription repression of PML::RARA, so promyelocytes mature into neutrophils; arsenic trioxide also degrades the fusion protein. CD33 binding describes antibody-drug conjugates.