MLT GlobeSCFHS exam preparation (Saudi Arabia) – page 3
749 practice MCQs for the SCFHS medical laboratory exam. Level: Intermediate.
Rh antigens are carried on which type of red cell membrane structure?
RhD and RhCE are nonglycosylated proteins that cross the membrane about 12 times. This is why Rh antigens are protein-based, unlike carbohydrate ABO and Lewis antigens.
In Wiener notation, the haplotype R1 corresponds to which Fisher-Race antigens?
R1 = DCe, R2 = DcE, R0 = Dce, and r' = dCe. Capital R shows D is present; the subscript or prime shows C/E antigens.
How does treatment of red cells with proteolytic enzymes such as papain affect Rh antigen reactions?
Enzymes remove sialic acid-rich glycoproteins, reduce surface charge and expose Rh antigens, so Rh antibody reactions are stronger.
A 25-year-old D-negative woman needs emergency red cells before her type is fully confirmed. The best choice is:
Females of childbearing potential receive group O, D-negative red cells in emergencies to avoid anti-D and future HDFN.
What is the most common cause of fatal acute hemolytic transfusion reactions?
Most fatal acute hemolytic reactions are ABO incompatibilities caused by clerical errors, such as a wrong patient or mislabelled sample. Missed weak antibodies usually cause delayed reactions instead.
Which mechanism explains the severity of an ABO-incompatible acute hemolytic reaction?
Anti-A and anti-B are mainly IgM and activate complement through C9, lysing cells in the circulation. This can lead to shock, DIC and acute kidney injury.
The Clark electrode measures:
The Clark electrode is amperometric: oxygen diffuses through a membrane and is reduced at a platinum cathode, producing current proportional to pO2. The Severinghaus electrode measures pCO2.
On a blood gas analyser, bicarbonate is usually:
Blood gas analysers measure pH, pCO2 and pO2 and derive HCO3− using Henderson–Hasselbalch. Chemistry analysers measure total CO2 enzymatically or by ISE.
Which change shifts the oxyhemoglobin dissociation curve to the left (increased oxygen affinity)?
Alkalosis, hypothermia, low 2,3-BPG, carboxyhemoglobin and fetal hemoglobin shift the curve to the left. Acidosis, fever, high CO2 and high 2,3-BPG shift it to the right.
For lactate measurement, the blood sample should be:
Glycolysis in red and white cells continues after collection and raises lactate. Prolonged tourniquet and fist clenching also increase lactate. Fluoride tubes or prompt analysis on ice are advised.
In the hexokinase method for glucose, which change is measured?
Hexokinase converts glucose to glucose-6-phosphate; G6PD then oxidises it and reduces NADP+ to NADPH, raising absorbance at 340 nm. Hydrogen peroxide and dye colour belong to the glucose oxidase (Trinder) method.
For a standard adult oral glucose tolerance test, the glucose load given after an overnight fast is:
The WHO/ADA adult OGTT uses 75 g of anhydrous glucose dissolved in water, with a 2-hour sample. 50 g is used for the non-fasting screening step in pregnancy.
HbA1c mainly reflects average blood glucose over the previous:
Glycation is slow and lasts for the life of the red cell (about 120 days), so HbA1c reflects the last 2–3 months. Fructosamine reflects 2–3 weeks.
The sodium ion-selective electrode most commonly uses a membrane made of:
Sodium ISEs use aluminium silicate glass membranes (or ionophores in some systems). Valinomycin is the ionophore used for potassium electrodes.
Which condition causes a high anion gap metabolic acidosis?
Ketoacids (beta-hydroxybutyrate, acetoacetate) are unmeasured anions that raise the anion gap. Diarrhoea, RTA and carbonic anhydrase inhibitors cause normal-gap (hyperchloremic) acidosis.
In central diabetes insipidus, which laboratory pattern is typical?
Lack of ADH prevents water reabsorption, producing large volumes of dilute urine, with rising plasma sodium and osmolality if water intake is limited.
Which antibody is most useful for confirming autoimmune (Hashimoto) thyroiditis?
Anti-TPO antibodies are present in most patients with Hashimoto thyroiditis. TSH-receptor antibodies are characteristic of Graves disease.
A healthy 14-year-old boy has ALP twice the adult upper reference limit, with normal GGT, ALT and bilirubin. The most likely reason is:
Osteoblast activity during growth raises bone ALP in children and adolescents, so pediatric reference intervals are higher. Normal GGT and other liver tests argue against a liver cause.
Total cholesterol 220 mg/dL, HDL cholesterol 50 mg/dL, triglycerides 150 mg/dL. What is the LDL cholesterol by the Friedewald equation?
LDL = TC − HDL − TG/5 = 220 − 50 − 30 = 140 mg/dL. 170 mg/dL is non-HDL cholesterol, which forgets to subtract VLDL.
Unconjugated bilirubin is carried in plasma to the liver mainly bound to:
Unconjugated bilirubin is water-insoluble and travels tightly bound to albumin. Ligandin is an intracellular carrier protein inside hepatocytes, not a plasma carrier.