MLT GlobeASCP exam preparation (USA · MLS / MLT) – page 38
1200 practice MCQs for the ASCP medical laboratory exam. Level: Advanced.
A patient with a leaking mechanical aortic valve has anemia, schistocytes, high LDH, low haptoglobin and a negative DAT. Over months, which deficiency is most likely to develop?
Ongoing mechanical intravascular hemolysis causes loss of iron in urine as hemoglobin and hemosiderin, leading to iron deficiency. B12 is not lost in hemolysis.
A marathon runner passes red-brown urine after a race. Plasma is pink, haptoglobin is low, and urine microscopy shows few red cells despite a strongly positive blood dipstick. The most likely cause is:
Repeated foot strike damages red cells in the sole, causing intravascular hemolysis with pink plasma and low haptoglobin. Myoglobin does not color plasma or lower haptoglobin, and hematuria shows many red cells.
Warfarin lowers active vitamin K–dependent factors by inhibiting which enzyme?
Warfarin blocks VKORC1, preventing recycling of vitamin K to its active reduced form. Variants in VKORC1 and CYP2C9 explain much of the variation in warfarin dose requirements.
D-dimer is more specific for active clot formation and breakdown than total FDPs because it:
D-dimer contains two D domains joined by factor XIIIa cross-links, which exist only in stabilized fibrin. Other FDPs can come from fibrinogen breakdown without clot formation.
The main circulating inhibitor that rapidly neutralizes free plasmin is:
Alpha-2-antiplasmin quickly binds free plasmin, limiting fibrinolysis to the clot surface. Its inherited deficiency causes a bleeding tendency. Antithrombin mainly inhibits thrombin and Xa.
The ISTH overt DIC score uses which combination of tests?
The ISTH score gives points for platelet count, D-dimer/FDP, PT prolongation and fibrinogen; a score of 5 or more is compatible with overt DIC. The aPTT is not part of the score.
Low-molecular-weight heparin causes little prolongation of the aPTT because it:
Most LMWH chains are too short to bridge antithrombin to thrombin, so anti-Xa activity dominates. Anti-Xa assays are used when monitoring is needed.
According to ISTH guidance, lupus anticoagulant testing should use:
Two tests based on different principles (dRVVT and an LA-sensitive aPTT) are recommended, each with screen, mix and confirm steps. Anticardiolipin ELISA detects antibodies but not LA activity.
A patient has a positive lupus anticoagulant test after a DVT. To support antiphospholipid syndrome, the test should be repeated after at least:
Laboratory criteria require persistent positivity on two occasions at least 12 weeks apart, because transient antibodies occur with infections or drugs.
Desmopressin (DDAVP) is used in mild hemophilia A and type 1 vWD because it:
DDAVP releases stored VWF from Weibel-Palade bodies, raising VWF and factor VIII 2–5 fold. Tranexamic acid, not DDAVP, inhibits fibrinolysis.
Which substances are stored in platelet alpha granules?
Alpha granules contain adhesive and growth proteins such as fibrinogen, VWF, platelet factor 4 and PDGF. ADP, serotonin and calcium are in dense granules.
In a manual platelet count, blood is diluted 1:100. A total of 180 platelets is counted in the two central large squares (1 mm² each, depth 0.1 mm). The platelet count is:
Count = cells ÷ volume counted × dilution = 180 ÷ (2 × 1 × 0.1 µL) × 100 = 90 000/µL = 90 × 10^9/L.
A patient's blood contains many microcytic red cells (MCV 55 fL). On an impedance analyzer, the platelet count may be:
Very small red cells fall into the platelet size window and are counted as platelets. An optical/fluorescent platelet count or smear estimate helps confirm the true count.
Ibuprofen affects platelet function differently from aspirin because ibuprofen:
NSAIDs such as ibuprofen are reversible COX inhibitors, so their effect ends once the drug is cleared. Aspirin acetylates COX-1 irreversibly for the platelet's life.
A newborn has thrombocytopenia with bilateral absent radii but normal thumbs. The most likely diagnosis is:
Thrombocytopenia–absent radius syndrome keeps the thumbs, while Fanconi anemia typically affects the thumbs as well as the radii. Wiskott-Aldrich shows small platelets and eczema.
A red cell volume histogram has a standard deviation of 11.2 fL and an MCV of 80 fL. What is the RDW-CV?
RDW-CV = (SD ÷ MCV) × 100 = (11.2 ÷ 80) × 100 = 14.0%. The value 11.2 is the RDW-SD-type figure in fL, not the CV.
Which vitamin B12 test measures the fraction that cells can take up and is considered an early marker of deficiency?
Only B12 bound to transcobalamin (about 20–30% of total) is delivered to cells, and it falls early in deficiency. Most serum B12 is on haptocorrin, which cells cannot use.
A patient with brisk hemolysis has an MCV of 104 fL with normal B12 and folate. The most likely reason for the raised MCV is:
Reticulocytes are about 20% larger than mature red cells, so marked reticulocytosis raises the MCV. Spherocytes and iron deficiency tend to lower, not raise, the MCV.
A woman with iron deficiency anemia shows no rise in Hb after 6 weeks of correctly taken oral iron and has no ongoing bleeding. Which condition should be tested for as a cause of poor iron absorption?
Celiac disease damages the duodenal mucosa where iron is absorbed and is a common cause of oral iron failure. The other conditions do not impair iron absorption.
Rouleaux form in multiple myeloma mainly because the increased plasma proteins:
Red cells normally repel each other because of their negative surface charge. High globulin or fibrinogen lowers this zeta potential, so cells stack like coins; binding to specific antigens would cause agglutination instead.