Hormonal Assays and Interpretation — MCQs
Which hormone is released when serum calcium levels decrease?
Which of the following hormones regulates blood levels of 1,25-OH-cholecalciferol positively?
Which of the following is the most useful investigation for thyroid function?
The most important regulator of serum 1,25(OH)2 vitamin D concentration is:
To assess thyroid profile of a newborn, which of the following is mandatory?
Adrenal reserve is best tested by means of infusion with
A 30-year-old female complaints of fatigue and is unable to gain weight. On examination, her body felt warm. Which of the following investigation can be helpful in reaching the diagnosis?
Thyroxine binding globulin (TBG) is increased in:
Which of the following organs are involved in the synthesis and activation of vitamin D?
3 beta hydroxysteroid dehydrogenase deficiency causes increased production of -
Hormonal Assays and Interpretation Indian Medical PG Practice Questions and MCQs
Question 1: Which hormone is released when serum calcium levels decrease?
- A. Parathormone (Correct Answer)
- B. Calcitonin
- C. Thyroxine
- D. Adrenaline
Explanation: ***Parathormone*** - **Parathormone (PTH)** is released from the **parathyroid glands** in response to **low serum calcium levels**. - Its primary function is to **increase serum calcium** by stimulating bone resorption, increasing renal reabsorption of calcium, and enhancing intestinal absorption of calcium (indirectly via vitamin D activation). *Calcitonin* - **Calcitonin** is released from the **thyroid gland** in response to **high serum calcium levels**. - Its main action is to **lower serum calcium** by inhibiting osteoclast activity and increasing renal calcium excretion. *Thyroxine* - **Thyroxine (T4)** is a thyroid hormone primarily involved in **metabolism**, growth, and development. - It does **not directly regulate** serum calcium levels. *Adrenaline* - **Adrenaline (epinephrine)** is a hormone released from the **adrenal glands** in response to stress. - It plays a role in the "fight or flight" response, affecting heart rate, blood pressure, and glucose metabolism, but **not calcium regulation**.
Question 2: Which of the following hormones regulates blood levels of 1,25-OH-cholecalciferol positively?
- A. Thyroxine
- B. Parathormone (Correct Answer)
- C. Calcitonin
- D. Insulin
Explanation: ***Parathormone*** - **Parathormone (PTH)** directly stimulates the **renal 1-alpha-hydroxylase** enzyme, which converts 25-hydroxycholecalciferol to its active form, **1,25-dihydroxycholecalciferol (calcitriol)**. - This activation is crucial for increasing **calcium absorption** from the gut and maintaining calcium homeostasis. *Thyroxine* - **Thyroxine** (thyroid hormone) primarily regulates **metabolism**, growth, and development. - It does not have a direct positive regulatory effect on the synthesis or blood levels of **1,25-OH-cholecalciferol**. *Calcitonin* - **Calcitonin** is a hormone that **lowers blood calcium levels** by inhibiting osteoclast activity and decreasing renal calcium reabsorption. - It does not positively regulate the production of **1,25-OH-cholecalciferol**; in fact, its actions are generally antagonistic to those influenced by active vitamin D. *Insulin* - **Insulin** is a key hormone in **glucose metabolism**, facilitating glucose uptake by cells and promoting glycogen synthesis. - It plays no direct role in the regulation or synthesis of **1,25-OH-cholecalciferol**.
Question 3: Which of the following is the most useful investigation for thyroid function?
- A. TSH (Correct Answer)
- B. T3
- C. T4
- D. Thyroglobulin
Explanation: TSH - **Thyroid-Stimulating Hormone (TSH)** is the most sensitive and specific test for assessing thyroid function as it reflects the feedback loop between the pituitary gland and the thyroid [1]. - An abnormal TSH level usually indicates either **hypothyroidism** (high TSH) or **hyperthyroidism** (low TSH), even before changes in T3 or T4 are apparent [1]. *T3* - **Triiodothyronine (T3)** is primarily used to confirm a diagnosis of hyperthyroidism, especially when T4 levels are normal but TSH is suppressed [1]. - It is less reliable for initial screening due to its **short half-life** and significant diurnal variation. [1] *T4* - **Thyroxine (T4)** is a good indicator of thyroid hormone production, but its levels can be affected by **protein binding** and non-thyroidal illnesses. - While total T4 is often included in a thyroid panel, **free T4** is more accurate as it reflects the metabolically active hormone not bound to proteins [1]. *Thyroglobulin* - **Thyroglobulin** is primarily used as a tumor marker for monitoring recurrence in patients with differentiated thyroid cancer after thyroidectomy [1]. - It plays no significant role in the initial **assessment of general thyroid function** or diagnosis of hyper/hypothyroidism [1].
Question 4: The most important regulator of serum 1,25(OH)2 vitamin D concentration is:
- A. Calcium levels in serum
- B. Magnesium levels in serum
- C. Parathyroid hormone (Correct Answer)
- D. 25-hydroxyvitamin D in serum
Explanation: ***Parathyroid hormone*** - **Parathyroid hormone (PTH)** directly stimulates the **kidney's 1-alpha hydroxylase** enzyme, which converts **25(OH)D** to its active form, **1,25(OH)2D (calcitriol)**. - This regulation is critical for maintaining **calcium and phosphate homeostasis**, with PTH levels increasing when serum calcium is low, thereby boosting 1,25(OH)2D production. *Calcium levels in serum* - While **low serum calcium** indirectly stimulates **PTH** release, which then regulates 1,25(OH)2 vitamin D, calcium itself is not the direct or most important regulator. - The direct regulatory action on the conversion enzyme is mediated by PTH. *Magnesium levels in serum* - **Magnesium** plays a cofactor role in various enzymatic reactions, including those involving vitamin D metabolism, but it is not a direct or primary regulator of **1,25(OH)2 vitamin D concentration**. - Severe **hypomagnesemia** can sometimes impair PTH secretion and action, indirectly affecting vitamin D, but this is a secondary effect. *25-hydroxyvitamin D in serum* - **25-hydroxyvitamin D** is the precursor to **1,25(OH)2 vitamin D**, and its availability limits the maximum potential production of the active form. - However, the *rate* of conversion into the active form and thus the *concentration* of 1,25(OH)2D is primarily dictated by PTH, not the precursor itself.
Question 5: To assess thyroid profile of a newborn, which of the following is mandatory?
- A. Measure T3 only
- B. Measure TSH only
- C. Measure both TSH and T4 (Correct Answer)
- D. Measure T4 only
Explanation: ***Measure both TSH and T4*** - **Newborn screening** for congenital hypothyroidism typically involves measuring both **TSH** (thyroid-stimulating hormone) and **T4** (thyroxine). - Elevated TSH levels indicate **primary hypothyroidism**, where the thyroid gland is underactive, while low T4 levels confirm the reduced thyroid hormone production. *Measure T3 only* - **T3 (triiodothyronine)** is generally not the primary screening test for congenital hypothyroidism in newborns. - While T3 is an active form of thyroid hormone, its levels can be influenced by various factors and are less reliable than TSH and T4 for initial screening. *Measure TSH only* - Measuring only **TSH** can detect primary hypothyroidism, but it doesn't provide a complete picture of thyroid function. - In cases of **central (secondary or tertiary) hypothyroidism**, TSH levels might be normal or low, while T4 levels are reduced, which would be missed if only TSH were measured. *Measure T4 only* - Measuring only **T4** can help identify low thyroid hormone levels, but it doesn't differentiate between primary and central hypothyroidism. - To properly assess the cause of low T4, **TSH levels** are crucial to determine if the problem lies within the thyroid gland itself or higher up in the pituitary/hypothalamic axis.
Question 6: Adrenal reserve is best tested by means of infusion with
- A. ACTH (Correct Answer)
- B. Metyrapone
- C. Corticosteroids
- D. LHRH
Explanation: ACTH - The **ACTH stimulation test**, also known as the **cosyntropin test**, is the most common dynamic test for assessing adrenal reserve. - Exogenous ACTH (cosyntropin) stimulates the adrenal glands to produce cortisol; a subnormal response indicates adrenal insufficiency. *Corticosteroids* - **Corticosteroids** are hormones (like cortisol) produced by the adrenal glands, or synthetic versions used as medications; they do not test adrenal reserve but rather *replace* adrenal function. - Administering corticosteroids would interfere with, rather than assess, the adrenal gland's ability to produce its own hormones. *LHRH* - **Luteinizing hormone-releasing hormone (LHRH)** is used to assess the function of the anterior pituitary gland and gonads, not the adrenal glands. - An LHRH stimulation test evaluates the pituitary's ability to release LH and FSH, which in turn stimulate gonadal hormone production. *Metyrapone* - The **metyrapone test** assesses the integrity of the **hypothalamic-pituitary-adrenal axis** by blocking cortisol synthesis, which should lead to an increase in ACTH and 11-deoxycortisol [1]. - While it evaluates a part of adrenal function, it is primarily used to differentiate between primary and secondary adrenal insufficiency, and not a direct measure of cortisol production capacity in response to stimulation.
Question 7: A 30-year-old female complaints of fatigue and is unable to gain weight. On examination, her body felt warm. Which of the following investigation can be helpful in reaching the diagnosis?
- A. Elevated TSH with normal thyroid hormone levels
- B. Elevated TSH with low thyroid hormone levels
- C. Normal TSH with abnormal thyroid hormone levels
- D. Suppressed TSH with elevated thyroid hormone levels (Correct Answer)
Explanation: Suppressed TSH with elevated thyroid hormone levels - The patient's symptoms of **fatigue** (despite being warm) and **difficulty gaining weight**, coupled with her body feeling **warm**, are classic signs of **hyperthyroidism**. [1] - In hyperthyroidism, the thyroid gland produces **excessive thyroid hormones (T3 and T4)**, which in turn **suppresses TSH** production from the pituitary gland through negative feedback. [2] *Elevated TSH with normal thyroid hormone levels* - This pattern is characteristic of **subclinical hypothyroidism**, where the thyroid gland is beginning to fail, leading to increased TSH to maintain normal thyroid hormone levels. [3] - The patient's symptoms of feeling warm and difficulty gaining weight are inconsistent with hypothyroidism. [1] *Elevated TSH with low thyroid hormone levels* - This indicates **primary hypothyroidism**, where the thyroid gland is underactive and produces insufficient thyroid hormones, leading to a compensatory rise in TSH. [2] - Hypothyroidism typically presents with **weight gain**, **cold intolerance**, and fatigue, which contradict the patient's presentation. [1] *Normal TSH with abnormal thyroid hormone levels* - This scenario usually suggests **central hypothyroidism** (pituitary or hypothalamic dysfunction affecting TSH production) or **thyroid hormone resistance**. [3] - While possible in some rare cases, it does not fit the typical clinical picture of hyperthyroidism presented by the patient's symptoms.
Question 8: Thyroxine binding globulin (TBG) is increased in:
- A. Pregnancy (Correct Answer)
- B. Cancer chemotherapy
- C. Nephrotic syndrome
- D. Glucocorticoid therapy
Explanation: ***Pregnancy*** - Estrogen levels are elevated during **pregnancy**, which leads to an increase in the synthesis of **TBG** by the liver. - Increased TBG binds more thyroid hormone, reducing free thyroid hormone levels, which then stimulates the thyroid gland to produce more. *Cancer chemotherapy* - Many **chemotherapeutic agents** can damage the liver or interfere with protein synthesis, potentially leading to a *decrease* in TBG and other plasma proteins. - Chemotherapy can also induce **hypothyroidism** directly or indirectly, which may alter thyroid hormone binding. *Nephrotic syndrome* - **Nephrotic syndrome** is characterized by significant proteinuria, where plasma proteins, including **TBG**, are lost through the kidneys in the urine. - This leads to a *decrease* in serum TBG levels, which can affect total thyroid hormone measurements but typically does not cause overt thyroid dysfunction due to compensatory mechanisms. *Glucocorticoid therapy* - **Glucocorticoids** (e.g., prednisone, dexamethasone) are known to *decrease* the hepatic synthesis of **TBG**. - This reduction in TBG can lead to lower total thyroid hormone levels without necessarily indicating thyroid gland dysfunction, as free thyroid hormone levels often remain normal.
Question 9: Which of the following organs are involved in the synthesis and activation of vitamin D?
- A. Liver and Skin
- B. Skin and Kidney
- C. Kidney and Liver
- D. All of the options (Correct Answer)
Explanation: ***All of the options*** - The **skin** synthesizes an inactive form of vitamin D (**cholecalciferol**) upon exposure to **UVB radiation**. - The **liver** performs the first hydroxylation step, converting **cholecalciferol** (vitamin D3) into **25-hydroxyvitamin D** (calcidiol). The **kidneys** then perform the final hydroxylation, converting **calcidiol** into the active form, **1,25-dihydroxyvitamin D** (calcitriol). *Liver and Skin* - While both the **liver** and **skin** play crucial roles in vitamin D metabolism, they do not encompass all necessary organs. - The **kidneys** are essential for the final activation step of vitamin D. *Skin and Kidney* - The **skin** synthesizes the precursor, and the **kidneys** perform the final activation step. - However, the **liver** is required for the initial hydroxylation of vitamin D. *Kidney and Liver* - The **kidney** is responsible for the final activation, and the **liver** for the initial hydroxylation. - This option misses the crucial role of the **skin** in the initial synthesis of vitamin D upon sun exposure.
Question 10: 3 beta hydroxysteroid dehydrogenase deficiency causes increased production of -
- A. DHEA (Correct Answer)
- B. Progesterone
- C. Deoxycortisol
- D. Estradiol
Explanation: ***DHEA*** - The enzyme **3 beta-hydroxysteroid dehydrogenase (3β-HSD)** is crucial for converting **delta-5 steroids (pregnenolone, 17-OH-pregnenolone, and DHEA)** into **delta-4 steroids (progesterone, 17-OH-progesterone, and androstenedione)**. - A **deficiency** in 3β-HSD leads to the accumulation of its substrates, particularly **DHEA (dehydroepiandrosterone)** and **17-OH-pregnenolone**, due to the impaired conversion in the steroid synthesis pathway. - Among the accumulated substrates, **DHEA** has weak androgenic activity, making it clinically significant in this enzyme deficiency. *Progesterone* - **Progesterone** is a delta-4 steroid, which is synthesized from **pregnenolone** via the action of **3β-HSD**. - A deficiency in this enzyme would **decrease** the production of progesterone, not increase it, as the enzyme is required for its synthesis. *Deoxycortisol* - **Deoxycortisol (11-deoxycortisol)** is a precursor to cortisol, formed later in the adrenal steroid synthesis pathway from **17-hydroxyprogesterone**. - Its production would be **decreased** by a 3β-HSD deficiency, as the pathway is blocked upstream, reducing the formation of downstream products like cortisol and its precursors. *Estradiol* - **Estradiol** is an estrogen, synthesized from androgens (like testosterone) via the enzyme **aromatase**. - A deficiency in 3β-HSD would impair the production of androgens like androstenedione and testosterone, which are precursors for estradiol, thereby leading to a **decrease** in estradiol levels, not an increase.
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