MLT GlobeSCFHS exam preparation (Saudi Arabia) – page 9
749 practice MCQs for the SCFHS medical laboratory exam. Level: Intermediate.
A peptide bond links:
A peptide (amide) bond forms between the α-carboxyl of one amino acid and the α-amino group of the next, releasing water. Linked cysteine sulfhydryls form disulfide bonds.
Specific serum proteins such as IgG, IgA, IgM, C3 and C4 are most commonly measured in routine laboratories by:
Antibody–antigen complexes scatter light (nephelometry) or reduce transmitted light (turbidimetry) in proportion to the protein concentration. Electrophoresis cannot measure individual proteins specifically.
In which organ is urea mainly synthesized?
Urea is made in hepatocytes by the urea cycle, which converts toxic ammonia from amino acid breakdown into urea. The kidney only excretes urea; it does not make it.
Serum creatinine is 2.0 mg/dL. What is this value in µmol/L?
Creatinine (mg/dL) × 88.4 = µmol/L, so 2.0 × 88.4 = 176.8, about 177 µmol/L. 88.4 µmol/L corresponds to only 1.0 mg/dL.
Dietary non-heme iron is absorbed in the duodenum mainly:
Duodenal cytochrome b reduces Fe3+ to Fe2+, which enters enterocytes via DMT1. Ferroportin exports iron from the cell into blood, where it is carried as Fe3+ on transferrin.
An automated digital morphology system has pre-classified the white cells on a smear. Before reporting, the correct practice is that:
Digital systems suggest classifications, but a trained person must verify and reclassify cells before results are released. A full manual repeat on every slide is not required.
The sodium lauryl sulfate (SLS) hemoglobin method is widely used on analyzers mainly because it:
SLS lyses red cells and forms a stable SLS-hemoglobin complex that correlates with the cyanmethemoglobin reference method without cyanide waste. Turbidity from lipids or high WBC can still interfere.
A healthy adult is found to have a single alpha-globin gene deletion (-α/αα). Which laboratory picture is most typical?
A silent carrier has three working alpha genes, so the blood count is usually normal or shows only slight microcytosis. HbH inclusions need three deleted genes, and raised HbA2 points to beta-thalassemia trait.
Which condition promotes HbS polymerization and red cell sickling?
Deoxygenation, acidosis, dehydration and cold favor HbS polymerization. HbF does not join the polymer, and alpha-thalassemia lowers MCHC, so both reduce sickling.
A transfusion-dependent patient with beta-thalassemia major is receiving iron chelation. Which laboratory test is most commonly used for routine monitoring of iron load?
Regular transfusion causes iron overload, and serum ferritin is the usual serial test to guide chelation (with MRI for organ iron). Haptoglobin reflects hemolysis, not iron stores.
A young adult with hereditary spherocytosis has recurrent right upper abdominal pain after meals. The most likely related complication is:
Chronic extravascular hemolysis raises bilirubin excretion into bile, forming pigment gallstones, which are common in hereditary spherocytosis. Portal thrombosis is linked with PNH, not HS.
Vitamin K is needed for which step in the synthesis of factors II, VII, IX and X?
Vitamin K is a cofactor for gamma-glutamyl carboxylase; the Gla residues let these factors bind calcium and phospholipid surfaces. Proteins C and S depend on the same step.
A light-blue citrate tube contains a small clot. The correct action is to:
Clotting consumes fibrinogen and factors and activates others, making results unreliable. Clotted coagulation samples must be rejected.
Megakaryocytes become large polyploid cells because they undergo:
Megakaryocytes replicate DNA without dividing (endomitosis), reaching 8N–64N ploidy, and then shed platelets from cytoplasmic extensions. They do not fuse or lose a nucleus to form platelets.
A pregnant woman at 36 weeks has a platelet count of 115 × 10^9/L. She had normal counts before pregnancy and has no bleeding or hypertension. The most likely cause is:
Gestational thrombocytopenia is mild (usually above 70 × 10^9/L), appears late in pregnancy and resolves after delivery. HELLP includes hypertension, hemolysis and raised liver enzymes.
A 24-year-old woman with heavy menstrual periods reports a strong craving to chew ice. This symptom is most typical of:
Pica, especially pagophagia (ice craving), is a classic symptom of iron deficiency and often improves quickly with iron. B12 and folate deficiency do not typically cause pica.
A patient on long-term treatment has MCV 112 fL with normal B12 and folate. Which drug most likely explains this by directly inhibiting DNA synthesis?
Hydroxyurea inhibits ribonucleotide reductase, slowing DNA synthesis and causing macrocytosis; MCV rise is even used to check adherence. The other drugs do not cause macrocytosis.
A patient with fatigue, cold intolerance and weight gain has MCV 103 fL, no hypersegmented neutrophils and normal B12 and folate. Which test is most useful next?
Hypothyroidism is a common cause of non-megaloblastic macrocytosis, and the symptoms support it. Ferritin, HPLC and G6PD address microcytic or hemolytic anemias.
Serum iron should ideally be collected in the morning after an overnight fast because serum iron:
Serum iron shows diurnal variation (usually higher in the morning) and rises after meals or supplements, so fasting morning samples give comparable results.
Marked anisocytosis on a blood smear is best reflected by which analyzer parameter?
RDW measures the spread of red cell volumes, which is what anisocytosis describes. MCH and MCHC describe hemoglobin content, and MPV refers to platelets.