Chemical Pathology — MCQ Bank — OmpathStudy

Question 1

SCLC patient presents with Na⁺ 118, urine osmolality 520, and is euvolemic. Which ectopic hormone is most likely responsible?

Accepted Answer

ADH → SIADH — Ectopic ADH causes SIADH — euvolemic hyponatraemia with concentrated urine. This is a classic paraneoplastic syndrome of SCLC.

Question 2

Which tumor marker combination is best for early detection of Hepatocellular Carcinoma (HCC)?

Accepted Answer

AFP + DCP/PIVKA-II — DCP (PIVKA-II) + AFP improves early HCC sensitivity. CEA/CA19-9 are GI markers; CA125/HE4 are ovarian.

Question 3

What is the most likely cause of hypercalcemia in a squamous-cell lung carcinoma patient WITHOUT bone metastases?

Accepted Answer

PTHrP — PTHrP mediates humoral hypercalcemia of malignancy — it binds PTH receptors and suppresses endogenous PTH. True ectopic PTH is exceedingly rare.

Question 4

A patient with Small Cell Lung Cancer (SCLC) has anti-VGCC antibodies, weakness that improves with repeated use. What is the diagnosis?

Accepted Answer

Lambert-Eaton Myasthenic Syndrome — LEMS is characterized by anti-VGCC antibodies that impair presynaptic ACh release. Strength paradoxically improves with repeated stimulation — the opposite of Myasthenia Gravis.

Question 5

Which tumor markers are used to monitor non-seminomatous testicular germ cell tumors?

Accepted Answer

AFP + β-hCG + LDH — AFP (yolk-sac), β-hCG (choriocarcinoma), and LDH are key markers for staging, prognosis, and monitoring of non-seminomatous germ cell tumors.

Question 6

Ectopic ACTH secretion from a lung tumor characteristically presents with

Accepted Answer

Very high cortisol + very high ACTH + hypokalaemic alkalosis, NOT suppressed by high-dose DST — Ectopic ACTH leads to bilateral adrenal hyperplasia, resulting in very high cortisol and hypokalemia with alkalosis. Unlike pituitary Cushing's, it is not suppressed by high-dose dexamethasone.

Question 7

Which malignancy is CA 125 primarily used to monitor?

Accepted Answer

Epithelial ovarian cancer — CA 125 is used to monitor treatment response and relapse in epithelial ovarian cancer. The combination with HE4 in the ROMA algorithm improves preoperative risk stratification.

Question 8

Which marker is elevated in medullary thyroid carcinoma and used for surveillance?

Accepted Answer

Calcitonin + CEA — Medullary thyroid carcinoma arises from parafollicular C cells. Calcitonin is the primary marker, with CEA being a secondary marker. Both can rise with tumor recurrence.

Question 9

A patient presents with secondary amenorrhea, galactorrhea, a prolactin level 200 ng/mL, and low FSH/LH. What is the diagnosis?

Accepted Answer

Prolactinoma — A prolactin level 200 ng/mL with galactorrhea and suppressed gonadotropins is highly suggestive of a prolactinoma. Premature ovarian failure typically presents with high FSH; PCOS usually shows an elevated LH:FSH ratio.

Question 10

A 35-year-old man presents with infertility, gynecomastia, small firm testes, a karyotype of 47,XXY, high FSH/LH, and low testosterone. What is the diagnosis?

Accepted Answer

Klinefelter syndrome — Klinefelter syndrome (47,XXY) is characterized by primary testicular failure, leading to high FSH/LH, low testosterone, small firm testes, azoospermia, and gynecomastia.

Question 11

A young man presents with anosmia, absent puberty, low LH/FSH/testosterone, and absent olfactory bulbs on MRI. What is the diagnosis?

Accepted Answer

Kallmann syndrome — Kallmann syndrome is caused by defective GnRH neuron migration, leading to hypogonadotropic hypogonadism and anosmia. Treatment involves pulsatile GnRH or gonadotropin replacement.

Question 12

What is the typical hormonal pattern in Turner syndrome (45,X0)?

Accepted Answer

High FSH, high LH, low oestrogen — Turner syndrome is associated with streak gonads, resulting in primary ovarian failure. This leads to very high FSH and LH (hypergonadotropic hypogonadism) and low oestrogen, causing primary amenorrhea.

Question 13

What is the characteristic hormone pattern in 21-hydroxylase deficiency?

Accepted Answer

Low cortisol, low aldosterone, high 17-OHP, high adrenal androgens — In 21-hydroxylase deficiency, 17-OHP accumulates and is shunted towards androgen production. Low cortisol leads to increased ACTH, causing adrenal hyperplasia. Aldosterone synthesis is also often impaired, leading to salt wasting in the classic form.

Question 14

A woman presents with oligomenorrhea, acne, hirsutism, polycystic ovaries on ultrasound, and an LH:FSH ratio 2.5. What is the diagnosis?

Accepted Answer

PCOS — PCOS typically meets at least two of the Rotterdam criteria: oligo/anovulation, clinical/biochemical hyperandrogenism, and polycystic ovaries. It is the most common endocrine disorder in reproductive-age women.

Question 15

A 7-year-old boy presents with pubic hair development, accelerated bone age, prepubertal testes, and markedly elevated 17-OHP. What is the diagnosis?

Accepted Answer

CAH — 21-hydroxylase deficiency — Congenital Adrenal Hyperplasia (CAH) due to 21-hydroxylase deficiency causes virilization and advanced bone age due to excess adrenal androgens. The testes remain prepubertal because the androgen source is adrenal, not testicular.

Question 16

A patient has primary amenorrhea, breast development, absent pubic/axillary hair, a 46,XY karyotype, and male-range testosterone levels. What is the diagnosis?

Accepted Answer

Premature ovarian failure — Complete Androgen Insensitivity Syndrome (CAIS) in a 46,XY individual results in feminized external genitalia due to absent androgen receptors, despite functional testes. Breast development occurs due to estrogen conversion. Pubic and axillary hair are absent due to androgen insensitivity.

Question 17

How does constitutional delay of puberty differ from hypogonadotropic hypogonadism?

Accepted Answer

CDP progresses spontaneously without treatment; HH requires hormonal replacement — Constitutional delay of puberty is a normal variant where puberty occurs spontaneously, albeit delayed. Hypogonadotropic hypogonadism is a pathological condition requiring hormonal replacement therapy (GnRH or gonadotropins).

Question 18

What is the cause of central precocious puberty?

Accepted Answer

Premature activation of the hypothalamic-pituitary-gonadal axis — Central precocious puberty results from the premature activation of the hypothalamic-pituitary-gonadal axis, leading to pulsatile LH and FSH secretion and subsequent gonadal development. Peripheral precocious puberty is independent of this axis.

Question 19

Rapid virilization in a woman with markedly elevated DHEA-S and very high testosterone suggests

Accepted Answer

Adrenal carcinoma — Rapid virilization, especially with markedly elevated DHEA-S (an adrenal marker) and very high testosterone, is a red flag for adrenal carcinoma. PCOS and CAH typically cause more gradual and modest elevations.

Question 20

Which validated clinical scale is used to quantify hirsutism?

Accepted Answer

Ferriman-Gallwey score — The modified Ferriman-Gallwey (mFG) score assesses terminal hair growth in nine androgen-sensitive body areas. A score of ≥8 indicates clinically significant hirsutism.

Question 21

A semen analysis reveals a volume of 0.3 mL, pH 6.5, azoospermia, and absent fructose, with clear post-ejaculate urine. What is the diagnosis?

Accepted Answer

Bilateral ejaculatory duct obstruction / CBAVD — Low volume, acidic pH, azoospermia, and absent fructose in the ejaculate, along with clear post-ejaculate urine, are highly suggestive of ejaculatory duct obstruction or congenital bilateral absence of the vas deferens (CBAVD). Retrograde ejaculation would result in sperm being found in the post-ejaculate urine.

Question 22

According to WHO 2021 guidelines, what is the lower reference limit for progressive sperm motility?

Accepted Answer

30% — The WHO 2021 guidelines define the lower reference limit for progressive sperm motility as ≥30% and total motility as ≥42%. Below these thresholds, the condition is termed asthenozoospermia.

Question 23

A patient has azoospermia, elevated FSH, small testes, and a biopsy showing only Sertoli cells. What is the diagnosis?

Accepted Answer

Sertoli-cell-only syndrome — Sertoli-cell-only syndrome is characterized by a complete absence of germ cells. This leads to very high FSH levels due to the lack of inhibin B feedback from germ cells. Sperm retrieval for ICSI is generally not possible in this condition.

Question 24

What is the lower reference limit for sperm concentration according to WHO 2021?

Accepted Answer

16 million/mL — The WHO 2021 guidelines state that the lower reference limit for sperm concentration is ≥16 million/mL, with a total sperm count per ejaculate of ≥39 million. Concentrations below this are considered oligozoospermia.

Question 25

Anti-sperm antibodies most commonly develop after which event?

Accepted Answer

Vasectomy reversal or genital tract trauma/infection — Anti-sperm antibodies typically arise when the blood-testis barrier is disrupted, such as after vasectomy reversal, trauma, or infection (e.g., orchitis). These antibodies can impair sperm motility and penetration.

Question 26

Inhibin B, produced by Sertoli cells, is a marker of

Accepted Answer

Spermatogenesis quality — low in testicular failure — Inhibin B is a marker of spermatogenesis quality. Low levels of inhibin B, especially in conjunction with high FSH, indicate impaired testicular function. Normal inhibin B levels can suggest obstructive azoospermia.

Question 27

Which electrolyte imbalance potentiates digoxin toxicity?

Accepted Answer

Hypokalaemia — Potassium (K⁺) and digoxin compete for binding sites on the Na⁺/K⁺-ATPase. Hypokalemia leads to increased digoxin binding and toxicity, even at therapeutic levels. Hyperkalemia offers some protection.

Question 28

High anion gap metabolic acidosis with an elevated osmol gap and visual symptoms leading to blindness suggests ingestion of which toxic alcohol?

Accepted Answer

Methanol — Methanol is metabolized to formaldehyde and formic acid, causing a high anion gap metabolic acidosis and optic nerve toxicity leading to blindness. Ethylene glycol causes similar acidosis but primarily renal failure. Isopropanol causes an osmol gap but no acidosis.

Question 29

Adult salicylate poisoning typically produces which acid-base disturbance pattern?

Accepted Answer

Mixed respiratory alkalosis AND metabolic acidosis — Salicylates initially stimulate the respiratory center, causing respiratory alkalosis. At toxic doses, they uncouple oxidative phosphorylation, leading to metabolic acidosis. The combination of both is characteristic.

Question 30

The hepatotoxicity of paracetamol (acetaminophen) is primarily caused by

Accepted Answer

NAPQI accumulation when glutathione is depleted — Paracetamol is metabolized to NAPQI, a toxic metabolite normally conjugated with glutathione. Overdose depletes glutathione, allowing NAPQI to accumulate and cause centrilobular necrosis. N-acetylcysteine replenishes glutathione.

Question 31

What is the approximate therapeutic serum lithium range?

Accepted Answer

0.6–1.2 mmol/L — The therapeutic range for serum lithium is typically 0.6–1.2 mmol/L. Toxicity can occur above 1.5 mmol/L and becomes life-threatening above 2.0 mmol/L. Medications like NSAIDs and ACE inhibitors can increase lithium levels.

Question 32

Therapeutic Drug Monitoring (TDM) of vancomycin is used to prevent which complications while ensuring efficacy?

Accepted Answer

Nephrotoxicity and ototoxicity — Vancomycin trough monitoring (or AUC/MIC-guided dosing) is crucial to avoid nephrotoxicity (associated with high levels) and ototoxicity, while ensuring the drug concentration is sufficient for efficacy (preventing sub-therapeutic levels).

Question 33

In carbon monoxide poisoning, pulse oximetry is unreliable because

Accepted Answer

Pulse oximetry cannot distinguish COHb from OxyHb — gives falsely normal SpO₂ — Standard pulse oximeters are unable to differentiate between carboxyhemoglobin (COHb) and oxyhemoglobin (OxyHb), interpreting COHb as OxyHb. This leads to a falsely normal or elevated SpO₂ reading, masking the severity of CO poisoning. Co-oximetry is required for accurate diagnosis.

Question 34

What is the mechanism of organophosphate poisoning and its primary antidotes?

Accepted Answer

Irreversible AChE inhibition — antidote: atropine + pralidoxime — Organophosphates irreversibly inhibit acetylcholinesterase (AChE), leading to an accumulation of acetylcholine (ACh) at synapses. This causes muscarinic (DUMBELS symptoms) and nicotinic (weakness, fasciculations) effects. Atropine is used to block muscarinic effects, and pralidoxime can regenerate AChE if administered early.

Question 35

Which drug combination is most likely to trigger serotonin syndrome?

Accepted Answer

Tramadol + SSRIs — Tramadol inhibits serotonin reuptake. When combined with SSRIs or SNRIs, which also increase serotonin levels, it can lead to excessive serotonin in the synaptic cleft, causing serotonin syndrome characterized by hyperthermia, clonus, agitation, and autonomic instability.

Question 36

A neonate presents with a mousy odor, seizures, fair hair and skin, a positive Guthrie test, and elevated phenylalanine. What is the deficient enzyme?

Accepted Answer

Phenylalanine hydroxylase — This presentation is classic for Phenylketonuria (PKU), caused by a deficiency in phenylalanine hydroxylase (PAH). This leads to the accumulation of phenylalanine and its metabolites, which can cause intellectual disability if untreated.

Question 37

A patient presents with progressive liver disease, Kayser-Fleischer rings, neuropsychiatric symptoms, low caeruloplasmin, and elevated 24-hour urine copper. What is the diagnosis?

Accepted Answer

Wilson's disease — Wilson's disease is an autosomal recessive disorder of copper metabolism caused by mutations in the ATP7B gene. It leads to copper accumulation in the liver, basal ganglia, and cornea (Kayser-Fleischer rings), resulting in liver disease, neurological/psychiatric symptoms, and elevated urinary copper excretion. Caeruloplasmin levels are typically low.

Question 38

Which of the following is TRUE regarding primary and secondary adrenal insufficiency?

Accepted Answer

Secondary adrenal insufficiency has target gland atrophy — In primary adrenal insufficiency (e.g., Addison's disease), the adrenal glands fail, leading to low cortisol and high ACTH (due to loss of negative feedback). In secondary adrenal insufficiency, the pituitary fails to produce ACTH, leading to low ACTH and low cortisol; the adrenal glands become atrophic due to lack of stimulation.

Question 39

In the hypothalamic-pituitary-thyroid (HPT) axis, elevated free T4 levels cause

Accepted Answer

Suppression of TRH and TSH (negative feedback) — High levels of free T4 (and T3) exert negative feedback on the hypothalamus and pituitary, suppressing the release of TRH and TSH, respectively. This mechanism regulates thyroid hormone production.

Question 40

What is the gold standard test to assess both ACTH and Growth Hormone (GH) reserve simultaneously?

Accepted Answer

Insulin tolerance test (ITT) — The Insulin Tolerance Test (ITT), which induces hypoglycemia, is considered the gold standard for simultaneously assessing the integrity of the hypothalamic-pituitary-adrenal (HPA) axis (cortisol response to ACTH) and the somatotropic axis (GH response).

Question 41

An adult presents with enlarged hands and feet, jaw prognathism, and glucose intolerance. Laboratory tests show GH 1 ng/mL after an oral glucose tolerance test (OGTT) and elevated IGF-1. What is the diagnosis?

Accepted Answer

Acromegaly — Acromegaly is caused by excess GH secretion after epiphyseal closure. The diagnostic criteria include failure of GH suppression to <1 ng/mL after a 75g OGTT and elevated IGF-1. Clinical features include prognathism, macroglossia, and acral enlargement.

Question 42

Following bilateral adrenalectomy for Cushing's disease, a patient develops hyperpigmentation, an aggressive pituitary macroadenoma, and very high ACTH levels. What is the diagnosis?

Accepted Answer

Nelson's syndrome — Nelson's syndrome occurs when a pre-existing pituitary adenoma grows aggressively after the loss of negative feedback from cortisol following bilateral adrenalectomy. The unrestrained ACTH secretion leads to hyperpigmentation due to melanocortin receptor stimulation.

Question 43

A patient experiences a sudden severe headache, bitemporal hemianopia, and acute hypopituitarism. MRI reveals hemorrhage into a pituitary adenoma. What is the diagnosis?

Accepted Answer

Pituitary apoplexy — Pituitary apoplexy is an acute complication of a pituitary adenoma, characterized by hemorrhage or infarction within the tumor. It presents with sudden severe headache, visual disturbances (bitemporal hemianopia), ophthalmoplegia, and acute hypopituitarism, often presenting with adrenal insufficiency.

Question 44

Central diabetes insipidus is confirmed by which pattern?

Accepted Answer

Low urine osmolality (<300) + high serum osmolality/Na → corrects with DDAVP — Central DI is due to ADH deficiency, leading to the inability to concentrate urine despite high serum osmolality. Water deprivation fails to increase urine osmolality, but administration of DDAVP (a synthetic ADH analog) causes significant urine concentration. This distinguishes it from nephrogenic DI.

Question 45

What is the most common non-tumoral pharmacological cause of hyperprolactinemia?

Accepted Answer

Dopamine antagonists (metoclopramide, antipsychotics, domperidone) — Dopamine normally inhibits prolactin release from the pituitary. Drugs that block dopamine receptors, such as antipsychotics (e.g., risperidone), metoclopramide, and domperidone, are common causes of hyperprolactinemia.

Question 46

Sheehan's syndrome refers to

Accepted Answer

Pituitary infarction from severe post-partum haemorrhage — Sheehan's syndrome is ischemic necrosis of the pituitary gland resulting from severe hypotension or hemorrhage during childbirth. It commonly leads to hypopituitarism, including deficiencies in GH, ACTH, TSH, and gonadotropins, and is often recognized by the failure to lactate postpartum.

Question 47

In adults, growth hormone deficiency typically presents with

Accepted Answer

Reduced lean mass, increased fat mass, reduced bone density, fatigue — Adult growth hormone deficiency is associated with adverse changes in body composition (increased central adiposity, decreased lean mass), reduced bone mineral density, dyslipidemia, decreased quality of life, and fatigue.

Question 48

A patient has TSH <0.01, high fT4/fT3, a diffuse goiter, exophthalmos, pretibial myxedema, and is TRAb positive. What is the diagnosis?

Accepted Answer

Graves' disease — Graves' disease is an autoimmune disorder characterized by the production of TSH receptor antibodies (TRAb) that stimulate the thyroid gland, leading to diffuse goiter, thyrotoxicosis, and extrathyroidal manifestations like Graves' ophthalmopathy (exophthalmos) and pretibial myxedema.

Question 49

A patient has TSH 12 mIU/L, low fT4, high anti-TPO antibodies, fatigue, weight gain, and cold intolerance. What is the diagnosis?

Accepted Answer

Hashimoto's thyroiditis — Hashimoto's thyroiditis is the most common cause of primary hypothyroidism in iodine-sufficient areas. It is an autoimmune disorder characterized by lymphocytic infiltration of the thyroid gland and the presence of anti-thyroid peroxidase (anti-TPO) antibodies, leading to destruction of thyroid tissue and impaired hormone production.

Question 50

What is the characteristic sequence of thyroid function tests (TFTs) in subacute (De Quervain's) thyroiditis?

Accepted Answer

Hyperthyroidism → hypothyroidism → euthyroidism (recovery in most) — Subacute thyroiditis typically follows a triphasic course: an initial hyperthyroid phase (due to release of preformed thyroid hormone), followed by a hypothyroid phase (as thyroid hormone stores are depleted), and finally recovery to euthyroidism in most cases. It is often preceded by a viral upper respiratory infection and is associated with a markedly elevated ESR and very low radioactive iodine uptake.

Chemical Pathology — MCQ Bank — OmpathStudy

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