MLT GlobeDHA exam preparation (Dubai) – page 2
700 practice MCQs for the DHA medical laboratory exam. Level: Basic to intermediate.
CD8 is a transmembrane glycoprotein co-receptor characteristically found on:
CD8 binds MHC class I and marks cytotoxic T cells. Helper T cells carry CD4 and bind MHC class II. The older term 'suppressor T cell' is no longer used as a distinct CD8 category.
Which of these is the richest natural source of preformed vitamin A (retinol)?
Halibut and cod liver oils contain far more retinol than egg yolk or butter. Carrots provide β-carotene, a provitamin, not preformed vitamin A.
In advanced liver failure, rising blood ammonia is most damaging to which organ?
Ammonia crosses the blood–brain barrier and disturbs astrocyte glutamine metabolism and neurotransmission, causing hepatic encephalopathy. Other organs tolerate hyperammonaemia far better.
Red cells in G6PD deficiency haemolyse under oxidant stress because they cannot produce enough:
The HMP shunt, starting with G6PD, is the red cell's only NADPH source; NADPH keeps glutathione reduced to neutralise oxidants. ATP and NADH come from glycolysis.
In hepatic steatosis (fatty liver), the lipid that accumulates in hepatocytes is mainly:
Fatty liver results when triacylglycerol synthesis exceeds export as VLDL, as in alcohol excess, obesity or choline deficiency. Other lipids are minor components.
The rate-limiting enzyme of the hexose monophosphate (pentose phosphate) pathway is:
G6PD commits glucose-6-phosphate to the pathway and generates NADPH. α-Ketoglutarate and malate dehydrogenases are Krebs cycle enzymes.
Which molecule mainly couples energy-releasing catabolism to energy-requiring anabolism?
Catabolism regenerates ATP and anabolic reactions spend it. ADP is the discharged form, and cAMP is a signalling messenger, not an energy currency.
A patient has severe epigastric pain radiating to the back. Which serum enzyme is the most specific test for the likely diagnosis?
Lipase rises in acute pancreatitis and is more specific than amylase. ALP points to bone or biliary disease. Glucocerebrosidase is the enzyme deficient in Gaucher disease.
Which coenzyme carries an acyl group from one molecule to another, rather than carrying hydrogen or electrons?
CoA forms thioester bonds with acyl groups and transfers them. NAD+, NADP+ and FAD carry reducing equivalents in oxidation–reduction reactions.
Which enzyme belongs to the oxidative phase of the pentose phosphate pathway and produces NADPH?
The oxidative phase has two NADPH-producing steps: G6PD and 6-phosphogluconate dehydrogenase. Pyruvate kinase and aldolase are glycolytic enzymes.
Which of these vitamins is water-soluble?
Vitamin C is water-soluble and not stored in large amounts. Vitamins D (cholecalciferol), A (retinol) and E (tocopherol) are fat-soluble.
Calcitriol acts as a hormone on three main target tissues to raise plasma calcium. Which are they?
1,25-dihydroxyvitamin D increases intestinal calcium absorption, mobilises bone calcium with PTH, and increases renal calcium reabsorption.
During prolonged fasting, which organ makes ketone bodies but cannot use them itself?
Hepatic mitochondria make acetoacetate and beta-hydroxybutyrate. The liver lacks succinyl-CoA:3-ketoacid CoA transferase (thiophorase), so it exports ketones to other tissues.
A man on a diet with no fresh fruit or vegetables for months develops swollen bleeding gums and corkscrew hairs. Which vitamin is lacking?
These are signs of scurvy. Collagen hydroxylation fails without ascorbate, which weakens vessels and connective tissue.
How many cis double bonds does arachidonic acid (the precursor of prostaglandins) contain?
Arachidonic acid is 20:4 (omega-6), with double bonds at carbons 5, 8, 11 and 14. Docosahexaenoic acid has six.
A boy has recurrent joint bleeds and his maternal uncle had the same problem. Which description best fits his disorder?
Hemophilia A and B are X-linked recessive, so affected males inherit the gene through carrier mothers. Deep joint and muscle bleeds, not mucosal bleeding, are typical.
A CBC shows reduced red cells, white cells and platelets at the same time. What term describes this?
Pancytopenia means all three blood lineages are decreased, as seen in marrow failure or infiltration. Thrombocytopenia and leukopenia each refer to a single lineage.
Which range is typical for the red cell count of a healthy adult man?
Adult men usually have RBC counts of about 4.5–5.9 × 10^12/L, higher than women because testosterone stimulates erythropoietin. Use locally validated intervals.
How long does a normal red cell survive in the circulation?
Normal erythrocytes survive about 120 days before splenic macrophages remove them. Shortened survival defines hemolysis.
While scanning a normal blood film, which leukocyte is typically the largest?
Monocytes measure about 12–20 µm with abundant grey-blue cytoplasm and a folded nucleus; neutrophils and eosinophils are about 10–15 µm, small lymphocytes about 7–10 µm.