MLT GlobeDOH exam preparation (Abu Dhabi) – page 16
700 practice MCQs for the DOH medical laboratory exam. Level: Basic to intermediate.
Which laboratory finding is typical of untreated progressive HIV infection?
HIV destroys CD4+ T cells while CD8+ cells are often normal or increased, so the CD4:CD8 ratio falls below 1. B cells are present, often with polyclonal hypergammaglobulinaemia.
A specimen is labelled with the wrong patient's name at the bedside. This error occurs in which phase of testing?
Patient identification and specimen labelling happen before analysis, so it is a pre-analytical error, the phase where most laboratory errors occur. Analytical errors happen during measurement.
The reference range for total protein in adult lumbar CSF is approximately:
Normal lumbar CSF protein is about 15–45 mg/dL, much lower than plasma protein (60–80 g/L). Newborns have higher values.
CSF cell counts should be performed within about 1 hour of collection because:
Cells, especially neutrophils, start to disintegrate in CSF within about an hour, falsely lowering counts. Glucose loss affects chemistry, not the cell count.
What is the usual upper limit of the WBC count in normal synovial fluid?
Normal synovial fluid has fewer than about 200 WBCs/µL, mostly mononuclear cells. Counts of 2,000–50,000/µL suggest inflammatory arthritis.
During arthrocentesis, the first tube is bloody but later tubes become clearer. This pattern most likely indicates:
Blood from needle injury is uneven and decreases as aspiration continues. True joint haemorrhage gives uniformly bloody fluid in all tubes.
Amniotic fluid sent for bilirubin (ΔA450) measurement in suspected haemolytic disease of the fetus should be:
Bilirubin is broken down by light, which gives falsely low results. The specimen must be shielded from light immediately after collection.
An infant has sweat chloride of 72 mmol/L on two separate tests. The best interpretation is:
Sweat chloride of 60 mmol/L or more supports cystic fibrosis; 30–59 mmol/L is intermediate and below 30 is unlikely. Repeat positive tests with clinical findings confirm the diagnosis.
The nitrite pad of a reagent strip is based on which reaction?
Nitrite reacts with an aromatic amine to form a diazonium salt, which couples with a second compound to give a pink colour. Peroxidase activity is the basis of the blood pad.
Many round urothelial (transitional) epithelial cells with normal morphology are seen in a urine collected just after bladder catheterisation. This finding is most likely:
Catheterisation scrapes cells from the urothelium, so increased normal transitional cells are expected. Malignancy is suspected only when cells show abnormal nuclear features.
Large, flat urinary epithelial cells with abundant cytoplasm and a small central nucleus are most often:
These are squamous cells, the largest cells in sediment, and in large numbers suggest a poorly collected specimen. Renal tubular cells are smaller with an eccentric nucleus.
Which plasma protein carries iron from the gut and storage sites to developing red cells in the marrow?
Transferrin is the iron transport protein of plasma and delivers iron to erythroblasts through the transferrin receptor. Ferritin is the storage form, and haptoglobin binds free hemoglobin.
Intrinsic factor, needed for vitamin B12 absorption, is secreted by which cells?
Parietal cells of the stomach secrete both hydrochloric acid and intrinsic factor. Chief cells secrete pepsinogen, and the ileum is where the B12–intrinsic factor complex is absorbed.
Dietary folate is absorbed mainly in which part of the gut?
Folate is absorbed in the proximal small intestine (duodenum and jejunum). The terminal ileum is the site of vitamin B12 absorption.
Which pattern of red cell indices describes a microcytic hypochromic anemia?
Microcytic means a low MCV (small cells) and hypochromic means low hemoglobin per cell, shown by a low MCH (and often low MCHC). Iron deficiency is the classic example.
The movement of neutrophils out of blood vessels, squeezing between endothelial cells into the tissues, is called:
Diapedesis is the passage of leukocytes through the vessel wall. Chemotaxis is directed movement toward chemical signals, and margination is sticking to the vessel wall.
During platelet aggregation, fibrinogen forms bridges between platelets by binding to which receptor?
Activated GP IIb/IIIa (integrin αIIbβ3) binds fibrinogen, linking platelets together. GP Ib/IX/V binds von Willebrand factor for adhesion, and P2Y12 is an ADP receptor.
Primary hemostasis ends with the formation of:
Primary hemostasis is vessel constriction plus platelet adhesion and aggregation, forming a platelet plug. Secondary hemostasis (coagulation) then adds a stable fibrin mesh.
Which drug is given to reverse an overdose of unfractionated heparin?
Protamine sulfate binds heparin and neutralizes it. Vitamin K reverses warfarin, and tranexamic acid inhibits fibrinolysis.
Türk's solution for manual white cell counts lyses red cells because it contains:
Türk's fluid is dilute acetic acid, which lyses red cells, plus gentian violet, which stains white cell nuclei.