MLT GlobeDOH exam preparation (Abu Dhabi) – page 22
700 practice MCQs for the DOH medical laboratory exam. Level: Basic to intermediate.
Besides delivering oxygen, hemoglobin helps carry carbon dioxide from tissues, mainly by forming:
CO2 binds terminal amino groups of globin as carbaminohemoglobin, and deoxyhemoglobin buffers H+ from bicarbonate formation. Carboxyhemoglobin is bound carbon monoxide.
Which statement about the Philadelphia chromosome is correct?
The reciprocal translocation moves ABL1 onto BCR, leaving a small derivative 22. It arises in a stem cell, so lymphoid cells can carry it, and it also occurs in ALL.
In which condition are prophylactic platelet transfusions generally avoided because transfused platelets are rapidly destroyed?
In ITP, autoantibodies clear donor platelets as quickly as the patient's own, so transfusion is reserved for life-threatening bleeding. Production failure states respond well to platelets.
First-line treatment for newly diagnosed chronic-phase CML is currently:
Tyrosine kinase inhibitors induce deep molecular responses in most patients. Allogeneic transplantation is now reserved for resistance or advanced phases; hydroxyurea only controls counts.
Fever, confusion, platelets 12 × 10^9/L, schistocytes, normal PT/APTT and ADAMTS13 activity below 10%. The diagnosis is:
Severe ADAMTS13 deficiency defines TTP. DIC prolongs clotting times and lowers fibrinogen, ITP lacks schistocytes, and STEC-HUS has normal ADAMTS13 with prominent renal failure.
Whole blood collected into CPDA-1 and stored at 2–6 °C has a shelf life of:
Adenine in CPDA-1 extends storage to 35 days. CPD alone gives 21 days, and red cells in additive solutions such as SAGM keep for up to 42 days.
The genetic hallmark found in virtually all patients with CML is:
BCR::ABL1, detected by karyotype, FISH or PCR, defines CML. PML::RARA marks acute promyelocytic leukemia and JAK2 V617F the BCR::ABL1-negative MPNs.
In which condition is splenectomy generally contraindicated?
Splenectomy helps when the spleen destroys cells. In marrow failure the problem is production, so removing the spleen gives no benefit and adds infection risk.
MCV 103 fL, normal B12 and folate, and round macrocytes with target cells on the film. The most likely cause is:
Round macrocytes and target cells with normal vitamins suggest liver disease or alcohol. Megaloblastic anemia requires deficient B12 or folate; iron deficiency and thalassemia are microcytic.
Which clotting factor is NOT concentrated in cryoprecipitate?
Cryoprecipitate contains fibrinogen, factor VIII, von Willebrand factor, factor XIII and fibronectin. Vitamin K-dependent factors such as X and IX stay in the supernatant plasma.
A 5-year-old girl has had progressive pallor since 6 months of age and has hepatosplenomegaly. Which test is most useful for diagnosis?
Onset after 6 months, when γ chains switch to β, with pallor and organomegaly suggests β-thalassemia major, confirmed by raised HbF on electrophoresis or HPLC.
Which screening result is typical of hereditary spherocytosis?
Spherocytes have a reduced surface-to-volume ratio and lyse early in hypotonic saline. The EMA dye-binding flow test is now the preferred confirmatory test; DAT is negative.
A transfusion-dependent thalassemia patient with iron overload would be expected to show:
Transfused iron accumulates, saturating transferrin and raising ferritin. Low iron with high TIBC is iron deficiency; low iron with low TIBC is inflammation.
Which splenic function is most important for protection against encapsulated bacteria?
Red pulp macrophages and marginal zone B cells clear poorly opsonized encapsulated organisms and aged cells. The adult spleen does not normally produce blood cells.
Roughly what fraction of the body's platelets is normally pooled in the spleen?
About a third of platelets are held in the spleen. In hypersplenism this pool enlarges, lowering the blood count; after splenectomy the count rises.
Low MCV and MCH with a normal or high red cell count suggest:
Thalassemia produces many small, poorly hemoglobinized cells, so the RBC count is preserved. Megaloblastic anemia is macrocytic; aplastic anemia and leukemia are usually normocytic.
Why are people without a spleen at particular risk from Streptococcus pneumoniae?
The spleen's marginal zone B cells and macrophages handle encapsulated organisms. Nuclei are extruded in the marrow; the spleen only removes inclusions (pitting).
An automated platelet count is 58 × 10^9/L (350 × 10^9/L yesterday), and the EDTA film shows platelet clumps. Best next step?
EDTA-dependent antibodies can clump platelets (pseudothrombocytopenia). Citrate usually prevents clumping; multiply the count by 1.1 for the citrate dilution.
Which cause of gum abnormality produces tissue overgrowth rather than a bleeding tendency?
Phenytoin causes gingival hyperplasia. Thrombocytopenia and marrow failure cause bleeding gums, and vitamin C deficiency causes fragile vessels with swollen bleeding gums.
Which dietary factor decreases the absorption of non-heme iron?
Tannins and phytates bind iron into insoluble complexes. Ascorbic acid and gastric acid keep iron ferrous and soluble; meat enhances absorption. Iron deficiency itself increases absorption.