Why Correct: Vitamin K prophylaxis is administered intramuscularly to newborns to prevent hemorrhagic disease, which arises due to vitamin K deficiency and impaired synthesis of clotting factors II, VII, IX, and X.
Distractor Analysis: Vitamin E is a fat-soluble antioxidant that protects cell membranes from oxidative damage. Vitamin C is a water-soluble vitamin essential for collagen synthesis and immune function. Vitamin D regulates calcium and phosphate absorption for bone mineralization.
Takeaway: Vitamin K exists in two natural forms: K1 (phylloquinone) from green leafy vegetables and K2 (menaquinone) synthesized by gut bacteria.

Why Correct: Nine amino acids are essential for adult humans: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.
Distractor Analysis: Six amino acids are essential for rats, not humans. Twelve is the number of non-essential amino acids that humans can synthesize. Twenty is the total number of standard amino acids used in protein synthesis.
Takeaway: Conditionally essential amino acids like arginine, glutamine, and cysteine are normally non-essential but become essential during illness, stress, or infancy.

Why Correct: Twelve amino acids are classified as non-essential for humans because the body can synthesize them from metabolic intermediates.
Distractor Analysis: Nine is the number of essential amino acids required from diet. Fourteen would include conditionally essential amino acids such as arginine and glutamine. Twenty is the total number of standard amino acids encoded by the genetic code.
Takeaway: Conditionally essential amino acids like arginine, cysteine, glutamine, proline, and tyrosine become essential only under specific physiological conditions such as illness or infancy.

Why Correct: Louis Nicolas Vauquelin and his assistant Pierre Jean Robiquet isolated asparagine in 1806, marking the first discovery of an amino acid.
Distractor Analysis: Justus von Liebig studied nitrogen metabolism and classified foods into nitrogenous and non-nitrogenous. Emil Fischer determined the structures of many amino acids and synthesized peptides. Frederick Sanger determined the amino acid sequence of insulin.
Takeaway: The word 'protein' was coined by Jons Jacob Berzelius in 1838 to describe the complex nitrogenous substances found in all living organisms.

Why Correct: These eight plus histidine (making nine) are the essential amino acids that cannot be synthesized by the human body and must be obtained from diet.
Distractor Analysis: Non-essential amino acids (12 in number) can be synthesized by the body and are not required in the diet. Conditionally essential amino acids like arginine and glutamine become essential only under specific conditions. Complete proteins are dietary sources that contain all essential amino acids, not a category of amino acids themselves.
Takeaway: Essential amino acids must come from food, while non-essential can be made internally.

Why Correct: Essential amino acids cannot be synthesized by the human body and must be obtained from dietary sources.
Distractor Analysis: A: Incorrect; amino acids are small and easily absorbed. C: Incorrect; stomach acid digests proteins into amino acids. D: Incorrect; essential amino acids are found in both animal and plant proteins, though plant proteins may be incomplete.
Takeaway: The term 'essential' refers to the necessity of dietary intake because the body cannot produce these amino acids on its own.

Why Correct: Soy protein is a complete protein because it provides all nine essential amino acids in adequate proportions for human nutrition.
Distractor Analysis: All plant proteins are incomplete except for soy and quinoa. Casein from milk is a complete protein, not an incomplete one. Gelatin is an incomplete protein lacking tryptophan, not high in it.
Takeaway: Protein complementation is the practice of combining two incomplete plant proteins to obtain a complete amino acid profile, as in rice and beans.

Why Correct: Vitamin C deficiency leads to scurvy, with symptoms including bleeding gums, joint pain, anemia, and impaired wound healing due to collagen breakdown.
Distractor Analysis: Night blindness and dry skin are symptoms of Vitamin A deficiency, not Vitamin C. Bone deformities and rickets are caused by Vitamin D deficiency in children. Anemia due to folate deficiency arises from insufficient folic acid, a B-complex vitamin.
Takeaway: Albert Szent-Györgyi first isolated Vitamin C in 1928 and won the Nobel Prize in Physiology or Medicine in 1937 for discoveries related to biological combustion.

Why Correct: Acetic acid gives vinegar its sour taste and is widely used as a preservative and pickling agent.
Distractor Analysis: Ascorbic acid is Vitamin C, essential for collagen synthesis and immune function. Lactic acid accumulates in muscles during anaerobic respiration, causing fatigue. Muriatic acid is the common name for hydrochloric acid, a strong corrosive acid.
Takeaway: Acetic acid is produced by the fermentation of ethanol by Acetobacter bacteria, a process used in vinegar production.

Why Correct: Muriatic acid is the historical common name for hydrochloric acid (HCl), used in industrial cleaning and metal processing.
Distractor Analysis: Acetic acid is the organic acid that gives vinegar its characteristic sour taste and is used as a food preservative. Ascorbic acid is the chemical name of Vitamin C, essential for collagen synthesis and prevention of scurvy. Lactic acid is produced in muscles during anaerobic respiration and causes fatigue.
Takeaway: Hydrochloric acid is naturally secreted in the stomach as gastric juice, aiding digestion by activating pepsinogen to pepsin and killing ingested bacteria.

Why Correct: James Lind, a Scottish physician, conducted the first controlled clinical trial in 1747 on sailors with scurvy, showing that citrus fruits were effective.
Distractor Analysis: Albert Szent-Györgyi isolated Vitamin C in 1928 and won the Nobel Prize in 1937 for his work on biological combustion. Casimir Funk coined the term "vitamine" in 1912 and proposed the vitamin deficiency theory for beriberi. Frederick Gowland Hopkins discovered tryptophan in 1901 and shared the Nobel Prize in 1929 for his work on growth-promoting vitamins.
Takeaway: The name "ascorbic acid" is derived from "a-" meaning without and "scorbutus" meaning scurvy, literally translating to "anti-scurvy acid".

Why Correct: Albert Szent-Györgyi isolated Vitamin C in 1928 and won the Nobel Prize in Physiology or Medicine in 1937 for his work on biological combustion, including Vitamin C.
Distractor Analysis: Frederick Gowland Hopkins discovered vitamins and won the Nobel Prize in 1929 but did not isolate Vitamin C. James Lind conducted the first clinical trial showing citrus fruits cured scurvy in 1747, but did not isolate the vitamin. Linus Pauling won Nobel Prizes in Chemistry and Peace and promoted high-dose Vitamin C but did not discover or isolate it.
Takeaway: James Lind's 1747 controlled experiment on sailors proved citrus fruits prevent scurvy, laying the foundation for the later discovery of Vitamin C.

Why Correct: Vitamin C is a cofactor for prolyl and lysyl hydroxylase enzymes that stabilise collagen triple helix. Deficiency leads to unstable collagen, causing the classic scurvy symptoms of bleeding gums and poor wound healing.
Distractor Analysis: Elastin provides tissue elasticity and requires copper-dependent crosslinking, not Vitamin C. Keratin is a structural protein in hair, nails, and skin, synthesised independently of Vitamin C. Myosin is a motor protein in muscles involved in contraction, not affected by Vitamin C deficiency.
Takeaway: Vitamin C also enhances non-heme iron absorption from plant foods, making it important in preventing iron-deficiency anaemia.

Why Correct: Vitamin B1, also called thiamine, is a water-soluble vitamin whose deficiency causes beriberi, a disease affecting the nervous system and heart.
Distractor Analysis: Vitamin C deficiency causes scurvy, not beriberi. Vitamin B12 deficiency leads to pernicious anemia and neurological issues. Vitamin K is fat-soluble and its deficiency causes bleeding disorders.
Takeaway: Water-soluble vitamins include the B-complex group and vitamin C. Beriberi is specifically linked to thiamine deficiency, common in populations consuming polished rice.

Why Correct: Scurvy, caused by vitamin C deficiency, was a major cause of death among sailors during the Age of Exploration. British sailors carried limes and were called 'limeys' because citrus fruits prevented scurvy.
Distractor Analysis: Vitamin A deficiency causes night blindness and xerophthalmia. Vitamin D deficiency causes rickets in children and osteomalacia in adults. Niacin (vitamin B3) deficiency causes pellagra, characterized by dermatitis, diarrhea, and dementia.
Takeaway: James Cook's voyages successfully prevented scurvy by carrying sauerkraut, citrus fruits, and malt wort, demonstrating the importance of vitamin C before its discovery.

Why Correct: Vitamin A deficiency causes night blindness (nyctalopia) and xerophthalmia, a progressive eye disease that can lead to blindness.
Distractor Analysis: Vitamin C deficiency causes scurvy, characterized by bleeding gums and poor wound healing. Vitamin B1 (thiamine) deficiency causes beriberi, affecting the nervous and cardiovascular systems. Vitamin D deficiency causes rickets in children and osteomalacia in adults.
Takeaway: Xerophthalmia begins with night blindness and progresses to conjunctival dryness, Bitot's spots, and corneal ulceration. It is a leading preventable cause of childhood blindness in developing countries.

Why Correct: Pellagra is caused by niacin (vitamin B3) deficiency. The classic '3 Ds' are dermatitis, diarrhea, and dementia, and if untreated, a fourth D (death) follows.
Distractor Analysis: Vitamin C deficiency causes scurvy with bleeding gums and impaired wound healing. Vitamin A deficiency leads to night blindness and xerophthalmia. Vitamin B1 (thiamine) deficiency causes beriberi, affecting the nervous system and heart.
Takeaway: Pellagra was once endemic in populations subsisting on maize-based diets low in tryptophan, a precursor of niacin. Niacin can be synthesized from tryptophan in the body.

Why Correct: British sailors were called 'limeys' because they carried limes on long sea voyages to prevent scurvy due to their high vitamin C content.
Distractor Analysis: Apples contain some vitamin C but have no historical connection to scurvy prevention in the British Navy. Oranges and lemons also prevent scurvy, but the nickname 'limeys' specifically refers to limes, which were the standard issue for British sailors in the 19th century.
Takeaway: Scurvy prevention was crucial for naval powers; the British Navy officially mandated lime juice rations in 1795 after Lind's work.

Why Correct: Scurvy, caused by vitamin C deficiency, was historically prevented by consuming citrus fruits like limes. British sailors carried limes, earning them the nickname 'limeys'.
Distractor Analysis: Rickets is caused by vitamin D deficiency. Beriberi is caused by thiamine (vitamin B1) deficiency. Pellagra is caused by niacin (vitamin B3) deficiency.
Takeaway: Captain James Cook successfully prevented scurvy on his voyages by carrying sauerkraut, citrus fruits, and malt wort.

Why Correct: Vitamin C deficiency impairs collagen synthesis, causing weakened blood vessels, bleeding gums, poor wound healing, and joint pain — classic symptoms of scurvy.
Distractor Analysis: Vitamin A deficiency causes night blindness and xerophthalmia. Vitamin B3 (niacin) deficiency causes pellagra, with symptoms of dermatitis, diarrhea, and dementia. Vitamin D deficiency causes rickets in children and osteomalacia in adults.
Takeaway: Vitamin C is water-soluble and acts as a potent antioxidant; it also enhances intestinal iron absorption.

Why Correct: Riboflavin (vitamin B2) is highly photosensitive and rapidly degrades when exposed to light, especially ultraviolet light. This is why milk (a rich source of riboflavin) is often sold in opaque containers.
Distractor Analysis: Vitamin A is sensitive to heat and oxygen but not primarily to light; its degradation is accelerated by light but not as extreme as riboflavin. Vitamin C is destroyed by heat, oxygen, and metal ions, not primarily by light. Vitamin D is relatively stable to light; its synthesis in skin requires UV light.
Takeaway: Riboflavin in milk can be significantly reduced if milk is stored in clear glass bottles exposed to sunlight.

Why Correct: James Lind, a Scottish physician, conducted the first controlled clinical trial aboard HMS Salisbury in 1747. He divided 12 scurvy-stricken sailors into six groups and tested various treatments, proving that oranges and lemons cured scurvy within six days.
Distractor Analysis: John Woodall was a British military surgeon who recommended citrus fruits for scurvy in 1617, but did not conduct a trial. Sir Gilbert Blane was a Scottish physician who introduced lemon juice as a standard ration in the Royal Navy in 1795. Captain James Cook successfully prevented scurvy on his voyages by stocking fresh provisions and sauerkraut, but did not conduct a clinical trial.

Why Correct: Scurvy results from vitamin C deficiency, leading to impaired collagen synthesis. This causes bleeding gums, poor wound healing, joint pain, and easy bruising. Collagen is essential for connective tissue integrity.
Distractor Analysis: Night blindness is caused by vitamin A deficiency. Osteomalacia (adult rickets) results from vitamin D deficiency. Pellagra is caused by niacin (vitamin B3) deficiency, presenting with dermatitis, diarrhea, and dementia.

Why Correct: Vitamin C is water-soluble, not stored in the body, and excess is excreted in urine, necessitating daily dietary intake.
Distractor Analysis: Fat-soluble vitamins (A, D, E, K) are stored in the body. Vitamin C is not destroyed by stomach acid but is heat-sensitive. The human body cannot synthesize vitamin C due to lack of the enzyme L-gulonolactone oxidase.
Takeaway: Humans, primates, guinea pigs, and fruit bats are among the few mammals unable to synthesize vitamin C.

Why Correct: Vitamin C donates electrons to neutralise free radicals, shielding polyunsaturated fatty acids in cell membranes from lipid peroxidation.
Distractor Analysis: Mitochondrial DNA is protected primarily by mitochondrial antioxidants like glutathione. Ribosomal RNA is not a primary target of vitamin C. Cytoskeletal proteins are stabilised by other mechanisms.
Takeaway: Vitamin C regenerates vitamin E from its oxidised form, enhancing membrane protection synergistically.

Why Correct: Tannins in green tea and black tea chelate non-heme iron, forming insoluble complexes that reduce absorption.
Distractor Analysis: Orange juice is rich in vitamin C, which enhances non-heme iron absorption. Milk contains calcium, which moderately inhibits iron absorption but less potently than tannins. Lemon water provides vitamin C, enhancing iron absorption.
Takeaway: Vitamin C overcomes the inhibitory effect of tannins when consumed together with tea and an iron source.

Why Correct: Arginine is semi-essential because endogenous synthesis in adults is sufficient, but during periods of rapid growth (infancy, childhood) or stress, dietary intake becomes necessary.
Distractor Analysis: Arginine is required by infants and growing children, making it essential in those groups. Unlimited synthesis is not accurate as production is regulated. Essentiality varies with age, so it is not equally essential for all.
Takeaway: Histidine was once considered essential only in children but is now recognized as essential for adults as well; it is included in the list of nine essential amino acids.

Why Correct: Christiaan Eijkman discovered that beriberi was caused by a dietary deficiency, leading to the concept of essential nutrients. He later shared the Nobel Prize in 1929 for this work.
Distractor Analysis: Frederick Gowland Hopkins also researched accessory food factors (vitamins). Casimir Funk coined the term "vitamine" and isolated niacin. Luther Emmett Holt studied infant nutrition but did not establish the essential nutrients concept.
Takeaway: Eijkman's work on polished rice and beriberi in chickens demonstrated that the husk contained a substance essential for health, later identified as vitamin B1 (thiamine).

Why Correct: Casimir Funk coined the term 'vitamine' in 1912 from 'vital amine' to describe the accessory food factors he isolated from rice bran.
Distractor Analysis: Christiaan Eijkman discovered the dietary cause of beriberi. Frederick Gowland Hopkins received the Nobel Prize for discovering growth-stimulating vitamins. James Lind is known for identifying the cause of scurvy and advocating citrus fruits.
Takeaway: The 'e' was later dropped to become 'vitamin' after it was found that not all were amines.

Why Correct: Marasmus results from simultaneous deficiency of proteins and calories, while kwashiorkor involves primarily protein deficiency with adequate calorie intake. Edema is characteristic of kwashiorkor, not marasmus.
Distractor Analysis: Kwashiorkor is due to protein deficiency, not broadly essential amino acids, and marasmus is not a vitamin deficiency disease. Both conditions primarily affect children, not adults exclusively. Edema is a hallmark of kwashiorkor, while marasmus presents with severe wasting without edema.
Takeaway: The term 'kwashiorkor' originates from the Ga language of Ghana, meaning 'the disease the first child gets when the next child is born', reflecting its occurrence in weaning infants. This linguistic origin is a tested fact in Indian exams.

Why Correct: Arginine is considered semi-essential because the body can synthesize it in adequate amounts for adults, but during periods of growth or stress, dietary intake becomes necessary. Lysine, methionine, and threonine are essential amino acids that cannot be synthesized at any life stage.
Distractor Analysis: Lysine is an essential amino acid with no endogenous synthesis. Methionine is essential and also serves as a precursor for cysteine. Threonine is an essential amino acid required from the diet.
Takeaway: The nine essential amino acids for humans are histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. Histidine is essential only in infants, making it conditionally essential.

Why Correct: Meat, fish, dairy products, eggs, legumes, and soy products are rich sources of lysine. These animal-based and certain plant-based foods provide high lysine content.
Distractor Analysis: Leafy greens and citrus fruits are excellent sources of vitamins and minerals but are low in lysine. Whole grains and nuts are good sources of other amino acids but lysine is limiting in grains. Root vegetables and tubers are primarily carbohydrate sources with minimal protein content.
Takeaway: Cereal grains are deficient in lysine, making them incomplete proteins when consumed alone; combining grains with legumes provides all essential amino acids.

Why Correct: Dicoumarol is an antivitamin that acts as a vitamin K antagonist, interfering with blood clotting factor synthesis.
Distractor Analysis: Avidin binds biotin, methotrexate is a folic acid antagonist, and isoniazid is a pyridoxine antagonist.
Takeaway: Different antivitamins target different vitamins; dicoumarol is specific to vitamin K.

Why Correct: Karl Paul Link and his team at the University of Wisconsin isolated dicoumarol from spoiled sweet clover and identified it as the anticoagulant agent causing hemorrhagic disease in cattle. Distractor Analysis: Albert Szent-Györgyi discovered vitamin C. Frederick Gowland Hopkins discovered vitamins and essential amino acids. Casimir Funk coined the term 'vitamine'. Takeaway: Dicoumarol is a vitamin K antagonist antivitamin.

Why Correct: Isoniazid is an anti-tuberculosis drug that acts as a pyridoxine (vitamin B6) antagonist. It inhibits the activation of pyridoxine, leading to peripheral neuropathy as a side effect.
Distractor Analysis: Rifampicin inhibits bacterial RNA polymerase. Ethambutol inhibits arabinosyl transferase involved in cell wall synthesis. Pyrazinamide is converted to pyrazinoic acid which disrupts mycobacterial membrane potential.
Takeaway: The peripheral neuropathy caused by isoniazid is prevented by co-administering pyridoxine (vitamin B6) supplements during tuberculosis therapy.

Why Correct: An antivitamin is a substance that inhibits the action or absorption of a vitamin, often by acting as a structural analog. A provitamin is an inactive precursor that the body converts into an active vitamin, such as beta-carotene converted to vitamin A.
Distractor Analysis: The precursor that is converted into an active vitamin is a provitamin, not an antivitamin. Antivitamins and provitamins both occur naturally; for example, avidin in raw egg whites is a natural antivitamin. Antivitamins inhibit vitamin function, they do not enhance absorption.
Takeaway: Beta-carotene is the most commonly tested provitamin; it is a precursor of retinol (vitamin A) and is not an antivitamin.

Why Correct: Dicoumarol is an antivitamin that antagonizes vitamin K, inhibiting the synthesis of clotting factors II, VII, IX, and X.
Distractor Analysis: Warfarin is a synthetic derivative of dicoumarol and also a vitamin K antagonist, but not the parent compound found naturally in spoiled sweet clover. Heparin is an anticoagulant that activates antithrombin III, not a vitamin K antagonist. Aspirin is an antiplatelet drug that inhibits cyclooxygenase, not an antivitamin.
Takeaway: Dicoumarol was originally discovered in spoiled sweet clover as the cause of hemorrhagic disease in cattle.

Why Correct: Avidin is a glycoprotein in raw egg whites that binds irreversibly to biotin (vitamin B7), preventing its absorption and causing biotin deficiency.
Distractor Analysis: Thiamine (B1) is antagonized by pyrithiamine, a structural analog. Pyridoxine (B6) is antagonized by isoniazid, an anti-TB drug. Cobalamin (B12) is not known to be antagonized by a specific antivitamin found in food.
Takeaway: Cooking egg whites denatures avidin, eliminating its anti-biotin effect.

Why Correct: Methotrexate is a structural analog of folic acid that inhibits dihydrofolate reductase, blocking DNA synthesis and acting as an anticancer drug.
Distractor Analysis: Dicoumarol is a vitamin K antagonist used as an anticoagulant. Isoniazid is an anti-tuberculosis drug that acts as a pyridoxine (vitamin B6) antagonist. Warfarin is a synthetic derivative of dicoumarol and also a vitamin K antagonist.
Takeaway: Methotrexate is also used in autoimmune diseases like rheumatoid arthritis at lower doses, where its anti-inflammatory effects are exploited.

Why Correct: Paresthesia (numbness and tingling) and ataxia (loss of coordination) are neurological symptoms caused by vitamin B12 deficiency due to demyelination of peripheral nerves and the spinal cord. Folate deficiency does not cause neurological symptoms.
Distractor Analysis: Megaloblastic anemia occurs in both vitamin B12 and folate deficiencies, so it does not differentiate them. Glossitis (inflamed tongue) can occur in deficiencies of B12, folate, or iron, and is not specific. Fatigue is a non-specific symptom common to many anemias and does not help distinguish between B12 and folate deficiency.
Takeaway: Vitamin B12 requires intrinsic factor from gastric parietal cells for absorption; pernicious anemia results from autoimmune destruction of these cells, leading to B12 malabsorption. Folate deficiency does not cause neurological involvement.

Why Correct: Sir William Osler, the renowned Canadian physician, first provided a detailed description of pernicious anaemia and established its connection to gastric pathology.
Distractor Analysis: Lord Thomas Addison described Addison's disease (adrenal insufficiency), not pernicious anaemia. Dr. George R. Minot, along with Dr. William P. Murphy, discovered that liver therapy could treat pernicious anaemia, but they did not first describe the disease. Dr. William P. Murphy collaborated with Minot on the liver therapy discovery.
Takeaway: The liver therapy for pernicious anaemia was perfected by Minot and Murphy in 1926, for which they shared the Nobel Prize in Physiology or Medicine in 1934.

Why Correct: Vitamin B12 deficiency causes demyelination of the spinal cord's dorsal columns and corticospinal tracts along with peripheral nerves, leading to subacute combined degeneration of the cord.
Distractor Analysis: Parkinsonism is caused by dopamine depletion in the substantia nigra, not by B12 deficiency. Alzheimer disease involves amyloid plaques and neurofibrillary tangles, unrelated to B12. Peripheral neuropathy occurs but is not the exclusive pattern; spinal cord involvement is also characteristic.
Takeaway: Subacute combined degeneration of the spinal cord presents with paresthesias, ataxia, and spastic weakness — a triad that alerts clinicians to possible B12 deficiency even before anaemia develops.

Why Correct: Folate deficiency causes megaloblastic anaemia identical to B12 deficiency but does not cause neurological symptoms. Neurological involvement is the distinguishing feature of B12 deficiency.
Distractor Analysis: Vitamin B12 deficiency causes both megaloblastic anaemia and neurological symptoms. Vitamin B6 deficiency leads to microcytic anaemia, not megaloblastic. Iron deficiency causes microcytic hypochromic anaemia, not megaloblastic.
Takeaway: The Schilling test differentiates B12 malabsorption (pernicious anaemia) from dietary B12 deficiency; it uses radioactive B12 to measure absorption with and without intrinsic factor.

Why Correct: Parietal cells of the gastric mucosa secrete intrinsic factor, a glycoprotein essential for vitamin B12 absorption in the terminal ileum. Without intrinsic factor, B12 cannot be absorbed, leading to pernicious anaemia.
Distractor Analysis: Chief cells secrete pepsinogen, the precursor of pepsin. Goblet cells secrete mucus throughout the gastrointestinal tract. G cells secrete gastrin, a hormone that stimulates gastric acid secretion.
Takeaway: Parietal cells also secrete hydrochloric acid via H+/K+ ATPase (proton pump). Autoimmune destruction of parietal cells causes pernicious anaemia, detectable by anti-parietal cell and anti-intrinsic factor antibodies.

Why Correct: The Schilling test measures absorption of radioactive vitamin B12 to diagnose pernicious anaemia caused by intrinsic factor deficiency.
Distractor Analysis: Folic acid deficiency causes megaloblastic anaemia but is not detected by the Schilling test. Vitamin B6 deficiency causes microcytic anaemia and dermatitis. Vitamin B2 (riboflavin) deficiency causes angular stomatitis and cheilitis.
Takeaway: The Schilling test involves administering radioactive B12 orally and measuring urinary excretion; low excretion indicates impaired absorption due to lack of intrinsic factor.

Why Correct: Megaloblastic anaemia features macrocytic red blood cells with MCV >100 fL due to impaired DNA synthesis from B12 or folate deficiency.
Distractor Analysis: MCV 120 fL defines severe macrocytosis but the standard threshold for megaloblastic anaemia is >100 fL.
Takeaway: Hypersegmented neutrophils ( >5 lobes) are another hallmark of megaloblastic anaemia, often appearing before anaemia develops.