Disorders of Electrolyte Balance — MCQs

10 questions

A patient with SIADH would likely exhibit which electrolyte disturbance?

The body fluid compartments of a patient were measured, showing the following ion concentrations: - Sodium (Na): $10 \mathrm{mEq} / \mathrm{L}$ - Potassium (K): $140 \mathrm{mEq} / \mathrm{L}$ - Chloride (Cl): $15 \mathrm{mEq} / \mathrm{L}$ Based on these values, which fluid compartment is being described?

Secondary hyperparathyroidism due to Vit D deficiency shows :

All of the following are features of hyperkalemia on ECG, EXCEPT:

Which of the following causes hypocalcemia:

A breast fed child presents with hypernatremia (Serum sodium > 170m Eq/L). His urine sodium is 70 mEq/L. Which of the following is the most likely cause –

The normal range of serum osmolality (in mosm/L) is:

Normal anion gap is___ mmol/L?

Treatment of choice in severe dehydration is:

Q10

In which of the following conditions is blood osmolality increased?

Disorders of Electrolyte Balance Indian Medical PG Practice Questions and MCQs

Question 1: A patient with SIADH would likely exhibit which electrolyte disturbance?

A. Hyperkalemia
B. Hypokalemia
C. Hypernatremia
D. Hyponatremia (Correct Answer)

Explanation: **Hyponatremia** - **SIADH (Syndrome of Inappropriate Antidiuretic Hormone)** causes excessive secretion of ADH, leading to increased free water reabsorption and **dilutional hyponatremia** [1]. - The increased water retention dilutes the body's sodium concentration, resulting in a low serum sodium level [2]. *Hyperkalemia* - **Hyperkalemia** is an elevated potassium level and is not directly caused by SIADH. - While some conditions that cause SIADH might also affect potassium, it is not a direct consequence of ADH excess. *Hypokalemia* - **Hypokalemia**, or low potassium, is typically associated with conditions like diuretic use, vomiting, or diarrhea [2]. - SIADH primarily affects water balance and sodium concentration, not directly potassium levels. *Hypernatremia* - **Hypernatremia** is a high sodium level, which is the opposite of what occurs in SIADH [3]. - It results from conditions causing free water loss or insufficient water intake, not from excess ADH.

Question 2: The body fluid compartments of a patient were measured, showing the following ion concentrations: - Sodium (Na): $10 \mathrm{mEq} / \mathrm{L}$ - Potassium (K): $140 \mathrm{mEq} / \mathrm{L}$ - Chloride (Cl): $15 \mathrm{mEq} / \mathrm{L}$ Based on these values, which fluid compartment is being described?

A. Plasma
B. ICF (Correct Answer)
C. Interstitial fluid
D. ECF

Explanation: ***ICF*** - The measured ion concentrations, especially **high potassium (140 mEq/L)** and **low sodium (10 mEq/L)**, are characteristic of the **intracellular fluid (ICF)**, where potassium is the primary cation and sodium is kept low by the Na+/K+-ATPase pump. - **Chloride levels (15 mEq/L)** are also significantly lower in the ICF compared to extracellular fluids. *Plasma* - Plasma typically has **high sodium (around 140 mEq/L)** and **low potassium (around 4 mEq/L)**, which contradicts the given measurements. - Chloride levels in plasma are usually much higher, around **100-105 mEq/L**. *Interstitial fluid* - Interstitial fluid has an electrolyte composition very similar to plasma, with **high sodium** and **low potassium**, differing mainly in protein content. - This composition is not consistent with the given measurements. *ECF* - The ECF (extracellular fluid), which includes both plasma and interstitial fluid, is characterized by **high sodium** and **low potassium**. - The given ion concentrations, particularly the very **high potassium** and **low sodium**, are directly opposite to the typical ECF profile.

Question 3: Secondary hyperparathyroidism due to Vit D deficiency shows :

A. Hypocalcemia (Correct Answer)
B. Hypophosphatemia
C. Hypercalcemia
D. Hyperphosphatemia

Explanation: ***Hypocalcemia*** - **Vitamin D deficiency** leads to decreased intestinal absorption of calcium, causing **hypocalcemia** [3]. - This persistent **low serum calcium** is the primary stimulus for the parathyroid glands to increase PTH secretion, leading to secondary hyperparathyroidism [1], [2]. *Hypophosphatemia* - While PTH typically promotes phosphate excretion in the kidneys leading to hypophosphatemia, in **secondary hyperparathyroidism due to vitamin D deficiency**, the effect on phosphate can be variable [3]. - The goal of increased PTH is to raise calcium, and maintaining some level of phosphate is necessary for bone health and proper calcium regulation. Early or mild deficiency may not show significant hypophosphatemia. *Hypercalcemia* - **Hypercalcemia** is a characteristic feature of **primary hyperparathyroidism**, where the parathyroid glands autonomously overproduce PTH [1]. - In secondary hyperparathyroidism (due to vitamin D deficiency), the PTH is elevated in response to **low calcium**, and sustained significant hypercalcemia is not expected; in fact, the underlying problem is **hypocalcemia** [1]. *Hyperphosphatemia* - **PTH** generally acts to lower serum phosphate levels by promoting its renal excretion [2]. - Therefore, **hyperphosphatemia** is not typically observed in secondary hyperparathyroidism; rather, a more common finding would be normal or low phosphate due to the elevated PTH [3].

Question 4: All of the following are features of hyperkalemia on ECG, EXCEPT:

A. Shortened QT interval
B. Peaked T waves
C. Wide QRS complex
D. U waves (Correct Answer)

Explanation: ***U waves*** - **U waves** are typically associated with **hypokalemia**, not hyperkalemia. They are small deflections immediately following the T wave. - Their presence suggests an abnormality in myocardial repolarization due to low potassium levels. *Shortened QT interval* - A **shortened QT interval** is *not* a typical finding in hyperkalemia; hyperkalemia usually causes a **prolonged PR interval** and QRS widening, which can make QT measurement difficult but does not inherently shorten it. - A shortened QT interval is more commonly seen in conditions like **hypercalcemia** or inherited short QT syndrome. *Peaked T waves* - **Peaked T waves** (also known as "tenting" of the T waves) are one of the earliest and most classic ECG signs of hyperkalemia [1]. - This occurs due to abnormally rapid repolarization of the ventricles. *Wide QRS complex* - As hyperkalemia progresses, the **QRS complex widens** due to a slowing of intraventricular conduction [1]. - This widening can eventually lead to a **sine wave pattern** if not treated, indicating severe hyperkalemia and impending cardiac arrest.

Question 5: Which of the following causes hypocalcemia:

A. 1, 25-dihydroxycholecalciferol
B. Parathormone
C. Thyroid hormones
D. Calcitonin (Correct Answer)

Explanation: ***Calcitonin*** - **Calcitonin** is a hormone secreted by the **parafollicular cells (C cells)** of the thyroid gland. - It **lowers serum calcium levels** by **inhibiting osteoclast activity** (preventing bone resorption) and **increasing renal calcium excretion**. - This is the only hormone among the options that causes hypocalcemia. *1,25-dihydroxycholecalciferol* - This is the **active form of vitamin D** (calcitriol), which **increases serum calcium levels**. - It promotes intestinal calcium absorption, enhances bone resorption, and increases renal calcium reabsorption. - Deficiency of this hormone leads to hypocalcemia, but the hormone itself raises calcium. *Parathormone* - **Parathyroid hormone (PTH)** is the primary regulator that **increases serum calcium levels**. - It stimulates **osteoclast activity** (releasing calcium from bone), increases renal calcium reabsorption, and promotes synthesis of 1,25-dihydroxycholecalciferol. - PTH acts opposite to calcitonin in calcium homeostasis. *Thyroid hormones* - **Thyroxine (T4) and triiodothyronine (T3)** primarily regulate metabolism and have **no direct role in calcium homeostasis**. - While severe thyroid dysfunction can indirectly affect bone turnover, thyroid hormones do not directly cause hypocalcemia.

Question 6: A breast fed child presents with hypernatremia (Serum sodium > 170m Eq/L). His urine sodium is 70 mEq/L. Which of the following is the most likely cause –

A. Acute tubular necrosis
B. Severe dehydration
C. Excessive intake of sodium (Correct Answer)
D. Diabetes insipidus

Explanation: ***Excessive intake of sodium*** - A critically elevated **serum sodium (>170 mEq/L)** coupled with a high **urine sodium (70 mEq/L)** in a breastfed infant indicates that the kidneys are actively trying to excrete excess sodium. This pattern is consistent with an exogenous sodium overload. - This scenario suggests the ingestion of a **hypertonic solution** or food, likely by mistake, leading to significant sodium toxicity requiring rapid renal excretion. *Acute tubular necrosis* - In ATN, there's impaired renal concentration and reabsorption, but acute kidney injury often leads to **normonatremia or hyponatremia**, not severe hypernatremia. - While urine sodium can be high in ATN due to tubular damage, the primary cause of such extreme hypernatremia would typically be external sodium load. *Severe dehydration* - Severe dehydration usually causes **pre-renal acute kidney injury**, characterized by **high serum sodium** due to water loss, but the kidneys would **conserve sodium**, resulting in a very **low urine sodium** (<20 mEq/L). - The high urine sodium of 70 mEq/L in this case **argues against dehydration** as the primary cause of hypernatremia. *Diabetes insipidus* - Diabetes insipidus (DI) causes **hypernatremia due to free water loss** from the kidneys, resulting in a **dilute urine** with a **low urine osmolality** and typically **low urine sodium**. - The elevated urine sodium of 70 mEq/L is inconsistent with the renal handling of sodium seen in diabetes insipidus.

Question 7: The normal range of serum osmolality (in mosm/L) is:

A. 200 to 250
B. 280 to 295 (Correct Answer)
C. 300 to 320
D. 350 to 375

Explanation: ***280 to 295*** - This range represents the **physiological concentration** of solutes in the blood, primarily determined by sodium, glucose, and urea. - Maintaining osmolality within this **narrow range** is crucial for proper cellular function and fluid balance. *200 to 250* - A serum osmolality in this range would indicate **hypotonicity**, leading to water movement into cells and potential **cellular swelling**. - Values this low are typically seen in conditions like **severe hyponatremia** or excessive water intake. *300 to 320* - While slightly above the normal range, this might be seen in cases of **mild dehydration** or conditions like uncontrolled diabetes where blood glucose is elevated. - Sustained levels in this range indicate increased solute concentration, which can lead to **cellular dehydration**. *350 to 375* - This range represents significantly elevated serum osmolality, indicating **hypertonic states** such as severe dehydration, **hyperglycemic hyperosmolar state (HHS)**, or severe hypernatremia. - Such high osmolality would result in substantial **cellular shrinkage** and can be life-threatening.

Question 8: Normal anion gap is___ mmol/L?

A. 8-16 (Correct Answer)
B. 30-34
C. 20-24
D. 0-4

Explanation: ***8-16*** - The normal range for the **anion gap** is generally considered to be 8-16 mmol/L, reflecting the unmeasured anions in the plasma. - This range can vary slightly between laboratories, but **8-16 mmol/L** is the most commonly accepted range in clinical practice. *30-34* - This range is significantly **higher than normal** and would indicate a **high anion gap metabolic acidosis**, rather than a normal anion gap. - A high anion gap suggests an accumulation of **unmeasured acids** in the body, such as in lactic acidosis or ketoacidosis. *20-24* - This value is also **elevated** compared to the normal range, suggesting a high anion gap. - An anion gap in this range would prompt investigation into causes of **metabolic acidosis** with an increased anion gap. *0-4* - This range is significantly **lower than normal** and could indicate a **low or negative anion gap**, which is a rare finding. - A low anion gap is often associated with conditions like **hypoalbuminemia**, multiple myeloma (due to paraproteins), or severe hypernatremia.

Question 9: Treatment of choice in severe dehydration is:

A. Plasma
B. Isolyte P
C. Ringer lactate
D. Normal saline (Correct Answer)

Explanation: ***Normal saline*** - **Normal saline (0.9% sodium chloride)** is an isotonic solution, making it the preferred initial intravenous fluid for rapidly correcting severe dehydration and restoring intravascular volume [1]. - Its **electrolyte composition** closely mimics the body's extracellular fluid, minimizing osmotic shifts and providing effective volume expansion [1]. *Plasma* - **Plasma** is primarily used for expanding blood volume in cases of **hemorrhage** or severe **protein deficiency**, not for simple dehydration. - It carries risks of allergic reactions and disease transmission, making it inappropriate for routine dehydration treatment. *Isolyte P* - **Isolyte P** is a hypotonic solution, typically used for maintenance fluid therapy in children, especially in situations where **sodium restriction** is desirable. - It is not suitable for rapid volume expansion in severe dehydration due to its low sodium content, which could worsen hypotonicity in an already depleted patient. *Ringer lactate* - **Ringer's lactate** is an isotonic crystalloid solution often used for fluid resuscitation, but it contains **lactate**, which is metabolized in the liver to bicarbonate. - While generally safe, in severe shock situations with impaired liver function or lactic acidosis, the metabolism of lactate can be compromised, potentially exacerbating acidosis. **Normal saline** avoids this concern as a first-line agent [2].

Question 10: In which of the following conditions is blood osmolality increased?

A. SIADH
B. Psychogenic polydipsia
C. Diarrhea (Correct Answer)
D. Cerebral toxoplasmosis

Explanation: ***Diarrhea*** - Diarrhea leads to a significant loss of **water and electrolytes** from the body, primarily from the extracellular fluid compartment. - This imbalance causes **hemoconcentration** and an increase in the concentration of solutes in the blood, thereby raising blood osmolality. *SIADH* - **Syndrome of Inappropriate Antidiuretic Hormone (SIADH)** is characterized by excessive secretion of ADH, leading to **dilutional hyponatremia**. - The excess water retention dilutes the blood, resulting in **decreased serum osmolality**. *Psychogenic polydipsia* - This condition involves excessive water intake due to psychological factors, which causes **dilution of body fluids**. - The increased water volume without a proportional increase in solutes leads to **decreased plasma osmolality**. *Cerebral toxoplasmosis* - **Cerebral toxoplasmosis** is an opportunistic infection of the brain, typically seen in immunocompromised individuals. - It primarily causes neurological symptoms and **does not directly impact blood osmolality** unless complicated by other factors like dehydration or SIADH (which is not a primary effect).

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