MCQs on Serum Electrolytes

Which electrolyte imbalance is most commonly associated with cardiac arrhythmias?
• A) Hypernatremia
• B) Hypokalemia
• C) Hypercalcemia
• D) Hypomagnesemia
Answer: B) Hypokalemia
Explanation: Hypokalemia lowers resting membrane potential, increasing myocardial excitability, which can trigger arrhythmias. Causes include diuretics, vomiting, and diarrhea. ECG changes include U-wave prominence, T-wave flattening, and ST depression. Hyperkalemia also affects the heart but causes peaked T waves and widened QRS complexes.

Hyponatremia with high serum osmolality is usually due to:
• A) SIADH
• B) Hyperglycemia
• C) Diuretic use
• D) Addison’s disease
Answer: B) Hyperglycemia
Explanation: Hyperglycemia causes water to shift from intracellular to extracellular space, diluting serum sodium (pseudohyponatremia). Corrected sodium accounts for glucose levels. SIADH produces hypotonic hyponatremia, while Addison’s disease causes hyponatremia with hypovolemia.

The most common cause of hyperkalemia is:
• A) Excess dietary potassium
• B) Renal failure
• C) Insulin therapy
• D) Vomiting
Answer: B) Renal failure
Explanation: Decreased renal excretion due to acute or chronic kidney disease is the leading cause of hyperkalemia. Medications like ACE inhibitors, potassium-sparing diuretics, and metabolic acidosis exacerbate it. Hyperkalemia may result in muscle weakness and life-threatening arrhythmias.

Which electrolyte is primarily stored in bones and crucial for neuromuscular function?
• A) Sodium
• B) Calcium
• C) Magnesium
• D) Potassium
Answer: B) Calcium
Explanation: Calcium regulates muscle contraction, nerve transmission, and coagulation. About 99% is stored in bones. Hypocalcemia causes tetany, cramps, and prolonged QT interval. Hypercalcemia leads to constipation, renal stones, and cardiac conduction abnormalities.

Chvostek and Trousseau signs indicate:
• A) Hypernatremia
• B) Hypocalcemia
• C) Hypermagnesemia
• D) Hypokalemia
Answer: B) Hypocalcemia
Explanation: Hypocalcemia increases neuromuscular excitability, producing facial twitching (Chvostek) and carpal spasm (Trousseau). Causes include vitamin D deficiency, hypoparathyroidism, and renal failure. Hypercalcemia produces opposite effects, reducing neuromuscular excitability.

The major intracellular cation is:
• A) Sodium
• B) Potassium
• C) Calcium
• D) Magnesium
Answer: B) Potassium
Explanation: Potassium maintains cell membrane potential and nerve-muscle excitability. Serum potassium is a small fraction of total body potassium. Hypokalemia results from diuretics, vomiting, or diarrhea, while hyperkalemia often arises from renal failure or tissue breakdown.

Hypomagnesemia may cause:
• A) Muscle weakness
• B) Tremors and tetany
• C) QT prolongation and arrhythmias
• D) All of the above
Answer: D) All of the above
Explanation: Magnesium deficiency affects neuromuscular and cardiac function. It often coexists with hypokalemia and hypocalcemia. ECG may show prolonged QT and arrhythmias. Causes include alcoholism, malnutrition, diuretics, and gastrointestinal losses.

Hypernatremia is most commonly caused by:
• A) Water loss
• B) Salt overdose
• C) SIADH
• D) Addison’s disease
Answer: A) Water loss
Explanation: Hypernatremia usually results from free water loss (dehydration, diarrhea, diuretics). Less commonly, excessive sodium intake or impaired renal excretion contributes. Symptoms include thirst, confusion, seizures, and muscle weakness.

Which electrolyte abnormality is associated with peaked T waves on ECG?
• A) Hypokalemia
• B) Hyperkalemia
• C) Hypocalcemia
• D) Hypermagnesemia
Answer: B) Hyperkalemia
Explanation: Hyperkalemia increases cardiac excitability, producing peaked T waves, flattened P waves, and widened QRS. Severe hyperkalemia can cause ventricular fibrillation. Hypokalemia shows U waves and flattened T waves.

The main extracellular cation is:
• A) Sodium
• B) Potassium
• C) Calcium
• D) Magnesium
Answer: A) Sodium
Explanation: Sodium regulates extracellular fluid volume and osmolality. Hyponatremia and hypernatremia cause neurological symptoms due to cerebral edema or dehydration. Major sources of sodium are diet and renal conservation/excretion mechanisms.

Hypophosphatemia can lead to:
• A) Muscle weakness
• B) Respiratory failure
• C) Hemolysis
• D) All of the above
Answer: D) All of the above
Explanation: Low phosphate impairs ATP production, affecting muscle and red cell function. Severe hypophosphatemia may cause rhabdomyolysis, respiratory failure, hemolysis, and neurological disturbances.

The primary cause of hypokalemia in hospitalized patients is:
• A) Vomiting and diarrhea
• B) Loop and thiazide diuretics
• C) Insulin therapy
• D) All of the above
Answer: D) All of the above
Explanation: Hypokalemia in hospitalized patients is commonly due to GI losses, renal losses (diuretics), and intracellular shifts caused by insulin or alkalosis. ECG monitoring is essential due to arrhythmia risk.

Which electrolyte is required as a cofactor for many enzymatic reactions including ATPase activity?
• A) Sodium
• B) Magnesium
• C) Calcium
• D) Potassium
Answer: B) Magnesium
Explanation: Magnesium stabilizes ATP and acts as a cofactor in hundreds of enzymatic reactions. Deficiency can cause neuromuscular irritability, tetany, seizures, arrhythmias, and hypocalcemia or hypokalemia due to secondary effects.

Hypercalcemia is most commonly caused by:
• A) Vitamin D deficiency
• B) Primary hyperparathyroidism
• C) Chronic kidney disease
• D) Diuretics
Answer: B) Primary hyperparathyroidism
Explanation: Excess PTH increases bone resorption, renal calcium reabsorption, and intestinal absorption (via vitamin D), leading to hypercalcemia. Symptoms include polyuria, polydipsia, constipation, kidney stones, and neuropsychiatric disturbances.

Which condition leads to pseudohyperkalemia?
• A) Hemolysis during blood collection
• B) Acute renal failure
• C) Addison’s disease
• D) Diuretic therapy
Answer: A) Hemolysis during blood collection
Explanation: Pseudohyperkalemia occurs when in vitro cell lysis releases intracellular potassium. It is an artifact and does not reflect true serum potassium, unlike renal failure or hypoaldosteronism.

Which electrolyte disturbance prolongs the QT interval on ECG?
• A) Hypokalemia
• B) Hypocalcemia
• C) Hyperkalemia
• D) Hypernatremia
Answer: B) Hypocalcemia
Explanation: Low calcium delays ventricular repolarization, prolonging QT interval. Severe cases can trigger torsades de pointes. Hypercalcemia shortens QT, while potassium abnormalities affect T wave morphology and QRS duration.

SIADH causes:
• A) Hypernatremia
• B) Hyponatremia
• C) Hypokalemia
• D) Hyperkalemia
Answer: B) Hyponatremia
Explanation: SIADH results in water retention due to inappropriate ADH secretion, diluting serum sodium. Patients have euvolemic hyponatremia, low serum osmolality, concentrated urine, and normal renal, adrenal, and thyroid function.

Hypokalemia can result from:
• A) Diuretic use
• B) Vomiting or diarrhea
• C) Insulin therapy
• D) All of the above
Answer: D) All of the above
Explanation: Potassium loss occurs via renal (diuretics), GI (vomiting, diarrhea), or intracellular shifts (insulin, alkalosis). Symptoms include muscle weakness, cramps, constipation, and ECG changes like flattened T waves and U waves.

Which electrolyte is most important for maintaining bone mineralization?
• A) Sodium
• B) Calcium
• C) Potassium
• D) Magnesium
Answer: B) Calcium
Explanation: Calcium is essential for bone strength and mineralization, stored in hydroxyapatite. Deficiency causes rickets in children, osteomalacia in adults, and secondary hyperparathyroidism, while excess can lead to nephrolithiasis and neuropsychiatric symptoms.

The main anion of extracellular fluid is:
• A) Chloride
• B) Phosphate
• C) Bicarbonate
• D) Sulfate
Answer: A) Chloride
Explanation: Chloride maintains extracellular fluid balance and osmolarity. It follows sodium passively, contributing to acid-base balance. Hypochloremia occurs with vomiting or diuretics; hyperchloremia arises in dehydration or renal tubular acidosis.

Hypomagnesemia often coexists with:
• A) Hypokalemia
• B) Hypocalcemia
• C) Both A and B
• D) Hypernatremia
Answer: C) Both A and B
Explanation: Magnesium deficiency impairs potassium and calcium homeostasis, leading to refractory hypokalemia and hypocalcemia. Causes include malnutrition, alcohol use, diuretics, and gastrointestinal losses. ECG may show prolonged QT and torsades de pointes risk.

Rapid correction of chronic hyponatremia can cause:
• A) Cerebral edema
• B) Central pontine myelinolysis
• C) Seizures
• D) Hyperkalemia
Answer: B) Central pontine myelinolysis
Explanation: Overly rapid sodium correction (>8–10 mmol/L per 24 hours) can damage myelin in the pons, causing quadriplegia, dysarthria, and other neurological deficits. Careful gradual correction is critical in chronic hyponatremia.

The main intracellular anion is:
• A) Chloride
• B) Bicarbonate
• C) Phosphate
• D) Sulfate
Answer: C) Phosphate
Explanation: Phosphate resides predominantly intracellularly, forming ATP and nucleic acids. Hypophosphatemia impairs energy metabolism, causing muscle weakness, respiratory failure, hemolysis, and neurological deficits. Hyperphosphatemia is seen in renal failure or tissue breakdown.

Which electrolyte is essential for PTH secretion and action?
• A) Sodium
• B) Magnesium
• C) Calcium
• D) Potassium
Answer: B) Magnesium
Explanation: Magnesium is required for PTH secretion and responsiveness. Deficiency can lead to functional hypoparathyroidism and hypocalcemia resistant to calcium therapy. Causes include malnutrition, diuretics, alcoholism, and gastrointestinal losses.

Which electrolyte disorder can cause nephrogenic diabetes insipidus?
• A) Hypercalcemia
• B) Hypokalemia
• C) Both A and B
• D) Hypernatremia
Answer: C) Both A and B
Explanation: Hypercalcemia impairs renal concentrating ability via vasoconstriction and tubule dysfunction. Hypokalemia reduces aquaporin-2 expression in collecting ducts. Both disorders lead to polyuria, polydipsia, and risk of dehydration if untreated.

Which electrolyte disorder is associated with Trousseau and Chvostek signs?
• A) Hypercalcemia
• B) Hypocalcemia
• C) Hypermagnesemia
• D) Hypokalemia
Answer: B) Hypocalcemia
Explanation: Hypocalcemia increases neuromuscular excitability. Chvostek sign is facial twitching on tapping the facial nerve, and Trousseau sign is carpal spasm on BP cuff inflation. Causes include hypoparathyroidism, vitamin D deficiency, and renal failure. Hypercalcemia produces opposite effects, decreasing excitability.

The most common cause of hypernatremia is:
• A) Excess salt intake
• B) Water loss
• C) SIADH
• D) Hyperaldosteronism
Answer: B) Water loss
Explanation: Hypernatremia is usually due to water loss from fever, sweating, diarrhea, or diabetes insipidus. Excessive sodium intake or hyperaldosteronism is less common. Symptoms include thirst, irritability, confusion, seizures, and weakness.

Hyperkalemia can cause which ECG finding?
• A) Flattened T waves
• B) Peaked T waves
• C) U waves
• D) Prolonged QT interval
Answer: B) Peaked T waves
Explanation: Hyperkalemia increases myocardial excitability. ECG shows peaked T waves, flattened P waves, and widened QRS. Severe hyperkalemia may cause ventricular fibrillation or cardiac arrest. Prompt treatment with calcium, insulin-glucose, or dialysis is critical.

Sodium is the major:
• A) Intracellular cation
• B) Extracellular cation
• C) Intracellular anion
• D) Extracellular anion
Answer: B) Extracellular cation
Explanation: Sodium regulates extracellular fluid volume, osmolarity, and blood pressure. Normal serum levels are 135–145 mmol/L. Hyponatremia or hypernatremia causes neurological symptoms due to cerebral edema or dehydration, respectively. Kidneys tightly regulate sodium balance.

Which electrolyte deficiency is most likely in chronic alcoholism?
• A) Sodium
• B) Magnesium
• C) Potassium
• D) Calcium
Answer: B) Magnesium
Explanation: Chronic alcoholism leads to hypomagnesemia due to poor intake, malabsorption, and urinary losses. Magnesium deficiency can cause muscle cramps, tremors, seizures, arrhythmias, and hypocalcemia or hypokalemia. ECG may show prolonged QT interval and torsades de pointes risk.

Hypokalemia commonly results from:
• A) Diuretic therapy
• B) Vomiting and diarrhea
• C) Insulin administration
• D) All of the above
Answer: D) All of the above
Explanation: Hypokalemia occurs via renal losses (diuretics), gastrointestinal losses, or intracellular shift (insulin, alkalosis). Symptoms include muscle weakness, cramps, constipation, and arrhythmias. ECG may show flattened T waves, U waves, and ST depression.

The main anion in extracellular fluid is:
• A) Phosphate
• B) Chloride
• C) Bicarbonate
• D) Sulfate
Answer: B) Chloride
Explanation: Chloride maintains extracellular fluid balance and osmolarity. It passively follows sodium and participates in acid-base regulation. Hypochloremia occurs with vomiting or diuretics; hyperchloremia occurs with dehydration or renal tubular acidosis.

Hypophosphatemia can lead to:
• A) Muscle weakness
• B) Hemolysis
• C) Respiratory failure
• D) All of the above
Answer: D) All of the above
Explanation: Phosphate deficiency reduces ATP production, impairing muscle, red blood cell, and respiratory function. Severe hypophosphatemia can cause rhabdomyolysis, respiratory failure, hemolysis, and neurological deficits. Causes include malnutrition, alcoholism, and phosphate-binding drugs.

Hypercalcemia can cause:
• A) Constipation
• B) Polyuria and polydipsia
• C) Renal stones
• D) All of the above
Answer: D) All of the above
Explanation: Excess calcium reduces neuromuscular excitability and affects renal function. Common causes include hyperparathyroidism, malignancy, and vitamin D toxicity. Symptoms include constipation, polyuria, polydipsia, kidney stones, confusion, and arrhythmias.

SIADH causes which electrolyte abnormality?
• A) Hypernatremia
• B) Hyponatremia
• C) Hyperkalemia
• D) Hypokalemia
Answer: B) Hyponatremia
Explanation: SIADH leads to water retention without edema, diluting serum sodium (euvolemic hyponatremia). Urine osmolality is high, serum osmolality low, and renal, adrenal, and thyroid function are normal. Symptoms include nausea, confusion, seizures, and in severe cases, coma.

Rapid correction of chronic hyponatremia may cause:
• A) Cerebral edema
• B) Central pontine myelinolysis
• C) Seizures
• D) Hypokalemia
Answer: B) Central pontine myelinolysis
Explanation: Overly rapid correction (>8–10 mmol/L/24h) can damage myelin in the pons, causing quadriplegia, dysarthria, and neurological deficits. Gradual correction with careful monitoring of sodium is critical to prevent osmotic demyelination syndrome.

Which electrolyte is essential for PTH secretion and action?
• A) Calcium
• B) Sodium
• C) Magnesium
• D) Potassium
Answer: C) Magnesium
Explanation: Magnesium deficiency impairs PTH release and action, causing functional hypoparathyroidism and refractory hypocalcemia. Causes include malnutrition, alcoholism, diuretics, and gastrointestinal losses. Correcting magnesium restores calcium homeostasis.

Hypomagnesemia can lead to:
• A) Refractory hypokalemia
• B) Tetany
• C) Arrhythmias
• D) All of the above
Answer: D) All of the above
Explanation: Magnesium deficiency affects neuromuscular and cardiac function, causing muscle cramps, tetany, prolonged QT, torsades de pointes, and refractory hypokalemia. Causes include alcoholism, malnutrition, gastrointestinal losses, and diuretics.

The major intracellular anion is:
• A) Chloride
• B) Bicarbonate
• C) Phosphate
• D) Sulfate
Answer: C) Phosphate
Explanation: Phosphate is mostly intracellular, forming ATP and nucleic acids. Hypophosphatemia impairs energy metabolism, causing muscle weakness, respiratory failure, hemolysis, and neurological deficits. Hyperphosphatemia is often seen in renal failure or tissue breakdown.

Which electrolyte abnormality is associated with peaked T waves?
• A) Hypokalemia
• B) Hyperkalemia
• C) Hypocalcemia
• D) Hypermagnesemia
Answer: B) Hyperkalemia
Explanation: Hyperkalemia increases cardiac excitability. ECG shows peaked T waves, flattened P waves, and widened QRS. Severe hyperkalemia may result in ventricular fibrillation or cardiac arrest, requiring urgent treatment with calcium, insulin-glucose, or dialysis.

Hypokalemia ECG changes include:
• A) Flattened T waves and U waves
• B) Peaked T waves
• C) Shortened QT interval
• D) Wide QRS
Answer: A) Flattened T waves and U waves
Explanation: Hypokalemia decreases membrane excitability, producing flattened T waves, prominent U waves, ST depression, and arrhythmias. Causes include diuretics, vomiting, diarrhea, and intracellular potassium shifts due to insulin or alkalosis.

Hypercalcemia ECG changes include:
• A) Shortened QT interval
• B) Prolonged QT interval
• C) Peaked T waves
• D) U waves
Answer: A) Shortened QT interval
Explanation: Elevated calcium accelerates ventricular repolarization, shortening the QT interval. Severe hypercalcemia may cause arrhythmias, bradycardia, and hypertension. Common causes include primary hyperparathyroidism and malignancy.

Which electrolyte deficiency causes tetany resistant to calcium therapy?
• A) Sodium
• B) Magnesium
• C) Potassium
• D) Chloride
Answer: B) Magnesium
Explanation: Hypomagnesemia impairs PTH secretion and action, causing refractory hypocalcemia with tetany. Symptoms resolve only after magnesium correction. Common causes include alcoholism, malnutrition, diuretics, and gastrointestinal losses.

Which electrolyte disorder can cause nephrogenic diabetes insipidus?
• A) Hypercalcemia
• B) Hypokalemia
• C) Both A and B
• D) Hypernatremia
Answer: C) Both A and B
Explanation: Hypercalcemia impairs renal concentrating ability via vasoconstriction and tubular dysfunction. Hypokalemia reduces aquaporin-2 expression in collecting ducts. Both cause polyuria, polydipsia, and risk of dehydration.

Hyperphosphatemia is most commonly seen in:
• A) Chronic kidney disease
• B) Hypoparathyroidism
• C) Vitamin D deficiency
• D) Diuretic use
Answer: A) Chronic kidney disease
Explanation: Reduced phosphate excretion in CKD leads to hyperphosphatemia, causing secondary hyperparathyroidism, vascular calcification, and bone disease. High phosphate levels are also seen with tumor lysis or rhabdomyolysis.

Hypochloremia is commonly associated with:
• A) Vomiting
• B) Diuretics
• C) Metabolic alkalosis
• D) All of the above
Answer: D) All of the above
Explanation: Chloride loss occurs via vomiting, diuretics, or shifts during metabolic alkalosis. Low chloride can contribute to volume depletion, alkalosis, and electrolyte disturbances like hypokalemia.

The most abundant intracellular cation is:
• A) Sodium
• B) Potassium
• C) Calcium
• D) Magnesium
Answer: B) Potassium
Explanation: Potassium maintains resting membrane potential, nerve conduction, and muscle contraction. Intracellular potassium constitutes ~98% of total body potassium. Disorders include hypokalemia and hyperkalemia, both affecting cardiac function.

Hypokalemia may lead to which muscle condition?
• A) Muscle weakness
• B) Tetany
• C) Tremors
• D) Myotonia
Answer: A) Muscle weakness
Explanation: Low potassium impairs skeletal muscle excitability, causing weakness, cramps, and in severe cases, paralysis. ECG changes include flattened T waves, U waves, and arrhythmias.

Hypermagnesemia is most often caused by:
• A) Renal failure
• B) Excess magnesium intake
• C) Both A and B
• D) Diuretic therapy
Answer: C) Both A and B
Explanation: Renal failure reduces magnesium excretion, while excessive magnesium intake (antacids, laxatives) may raise levels. Symptoms include hypotension, bradycardia, hyporeflexia, respiratory depression, and arrhythmias.

Hypokalemia can result in which ECG abnormality?
• A) Peaked T waves
• B) Flattened T waves with U waves
• C) Shortened QT interval
• D) Widened QRS
Answer: B) Flattened T waves with U waves
Explanation: Low potassium prolongs repolarization, producing flattened T waves and prominent U waves. It increases risk of atrial and ventricular arrhythmias, especially in patients with underlying heart disease.

Hypernatremia primarily causes:
• A) Edema
• B) Neurological symptoms
• C) Arrhythmias
• D) Tetany
Answer: B) Neurological symptoms
Explanation: Hypernatremia increases plasma osmolality, causing water to shift from brain cells, leading to irritability, confusion, seizures, and coma. Causes include water loss (diabetes insipidus, diarrhea) or excessive sodium intake. Correction must be gradual to prevent cerebral edema.

Hypocalcemia may result in:
• A) Tetany
• B) Seizures
• C) Prolonged QT interval
• D) All of the above
Answer: D) All of the above
Explanation: Low calcium increases neuromuscular excitability, producing tetany, seizures, and ECG changes like prolonged QT. Causes include hypoparathyroidism, vitamin D deficiency, renal failure, and magnesium deficiency.

Which electrolyte disorder is associated with Torsades de Pointes?
• A) Hypokalemia
• B) Hypocalcemia
• C) Hypomagnesemia
• D) Hypernatremia
Answer: C) Hypomagnesemia
Explanation: Magnesium deficiency prolongs the QT interval, predisposing to Torsades de Pointes. Causes include alcoholism, malnutrition, diuretics, and GI losses. Correction of magnesium is crucial to prevent life-threatening arrhythmias.

Hyperkalemia can be caused by:
• A) Renal failure
• B) ACE inhibitors
• C) Tissue breakdown
• D) All of the above
Answer: D) All of the above
Explanation: Hyperkalemia arises from decreased renal excretion, drugs reducing aldosterone activity, or cellular release of potassium (rhabdomyolysis, hemolysis). Symptoms include weakness, paresthesia, and ECG changes like peaked T waves and widened QRS.

Which electrolyte regulates extracellular fluid volume and osmolarity?
• A) Potassium
• B) Sodium
• C) Calcium
• D) Magnesium
Answer: B) Sodium
Explanation: Sodium is the major extracellular cation. It determines plasma osmolality and volume. Hyponatremia or hypernatremia can cause neurological symptoms due to cerebral edema or dehydration, respectively. Renal regulation maintains sodium balance.

Hypokalemia is most commonly caused by:
• A) Diuretics
• B) Vomiting
• C) Intracellular shifts
• D) All of the above
Answer: D) All of the above
Explanation: Potassium losses occur via renal (diuretics), GI (vomiting, diarrhea), or intracellular shifts (insulin, alkalosis). ECG monitoring is essential because severe hypokalemia increases arrhythmia risk.

Hypercalcemia most commonly results from:
• A) Vitamin D deficiency
• B) Hyperparathyroidism
• C) Renal failure
• D) Diuretic therapy
Answer: B) Hyperparathyroidism
Explanation: Excess PTH increases bone resorption, renal calcium reabsorption, and intestinal absorption via vitamin D, causing hypercalcemia. Symptoms include constipation, polyuria, polydipsia, kidney stones, and neuropsychiatric disturbances.

Hypomagnesemia may lead to:
• A) Tetany
• B) Arrhythmias
• C) Refractory hypokalemia
• D) All of the above
Answer: D) All of the above
Explanation: Magnesium deficiency impairs neuromuscular and cardiac function, prolonging QT interval, causing tetany, and preventing potassium and calcium correction until magnesium is replenished. Causes include alcoholism, malnutrition, diuretics, and GI losses.

Which electrolyte is primarily intracellular?
• A) Sodium
• B) Potassium
• C) Chloride
• D) Bicarbonate
Answer: B) Potassium
Explanation: Potassium maintains resting membrane potential, nerve conduction, and muscle contraction. Intracellular potassium is ~98% of total body potassium. Hypokalemia or hyperkalemia affects cardiac and skeletal muscle function.

Hyperphosphatemia is most commonly seen in:
• A) Chronic kidney disease
• B) Hyperparathyroidism
• C) Vitamin D deficiency
• D) Diuretic therapy
Answer: A) Chronic kidney disease
Explanation: CKD reduces phosphate excretion, leading to hyperphosphatemia, which causes secondary hyperparathyroidism, vascular calcification, and bone disease. Other causes include tissue breakdown and tumor lysis syndrome.

Hypophosphatemia can cause:
• A) Muscle weakness
• B) Respiratory failure
• C) Hemolysis
• D) All of the above
Answer: D) All of the above
Explanation: Low phosphate impairs ATP production, affecting skeletal muscle, RBCs, and respiratory muscles. Causes include malnutrition, refeeding syndrome, alcohol abuse, and phosphate-binding drugs. Severe deficiency leads to rhabdomyolysis and neurological deficits.

Chloride is the major:
• A) Intracellular anion
• B) Extracellular anion
• C) Intracellular cation
• D) Extracellular cation
Answer: B) Extracellular anion
Explanation: Chloride follows sodium and helps maintain extracellular fluid osmolarity and acid-base balance. Hypochloremia occurs with vomiting or diuretics; hyperchloremia may arise in dehydration or renal tubular acidosis.

SIADH is characterized by:
• A) Hypernatremia
• B) Hyponatremia
• C) Hypokalemia
• D) Hyperkalemia
Answer: B) Hyponatremia
Explanation: SIADH leads to euvolemic hyponatremia with low serum osmolality and concentrated urine, caused by inappropriate ADH secretion. Renal, adrenal, and thyroid function are normal. Symptoms include nausea, confusion, seizures, and coma if severe.

Rapid correction of chronic hyponatremia may cause:
• A) Cerebral edema
• B) Central pontine myelinolysis
• C) Seizures
• D) Hypokalemia
Answer: B) Central pontine myelinolysis
Explanation: Rapid sodium correction (>8–10 mmol/L per 24h) causes osmotic demyelination, especially in the pons, resulting in quadriplegia, dysarthria, and neurological deficits. Gradual correction is essential.

Hypokalemia ECG changes include:
• A) Flattened T waves, U waves
• B) Peaked T waves
• C) Shortened QT
• D) Widened QRS
Answer: A) Flattened T waves, U waves
Explanation: Hypokalemia prolongs repolarization, producing flattened T waves, prominent U waves, ST depression, and arrhythmias. Causes include diuretics, vomiting, diarrhea, and intracellular shifts from insulin or alkalosis.

Hypercalcemia ECG change is:
• A) Shortened QT interval
• B) Prolonged QT interval
• C) Peaked T waves
• D) U waves
Answer: A) Shortened QT interval
Explanation: Elevated calcium accelerates ventricular repolarization, shortening QT interval. Severe hypercalcemia can cause arrhythmias, bradycardia, and hypertension. Primary hyperparathyroidism and malignancy are common causes.

Magnesium deficiency affects:
• A) PTH secretion
• B) Calcium and potassium levels
• C) Neuromuscular excitability
• D) All of the above
Answer: D) All of the above
Explanation: Magnesium deficiency impairs PTH release/action, causing refractory hypocalcemia, secondary hypokalemia, neuromuscular irritability, tetany, seizures, and arrhythmias. Causes include alcoholism, malnutrition, diuretics, and GI losses.

Hypermagnesemia is most often caused by:
• A) Renal failure
• B) Excess magnesium intake
• C) Both A and B
• D) Diuretic therapy
Answer: C) Both A and B
Explanation: Impaired renal excretion or excess intake (antacids, laxatives) causes elevated magnesium. Symptoms include hypotension, bradycardia, hyporeflexia, respiratory depression, and arrhythmias.

Hypokalemia can cause which neuromuscular effect?
• A) Tetany
• B) Muscle weakness
• C) Tremors
• D) Spasticity
Answer: B) Muscle weakness
Explanation: Low potassium reduces skeletal muscle excitability, causing weakness, cramps, and paralysis in severe cases. ECG changes include flattened T waves, U waves, and arrhythmias.

Hyperkalemia may result from:
• A) Renal failure
• B) Insulin deficiency
• C) Cellular breakdown
• D) All of the above
Answer: D) All of the above
Explanation: Decreased renal excretion, insulin deficiency, or release from cells (rhabdomyolysis, hemolysis) raises potassium. Symptoms include muscle weakness, paresthesia, and ECG changes (peaked T waves, widened QRS).

Pseudohyperkalemia is caused by:
• A) Hemolysis during blood draw
• B) Renal failure
• C) Addison’s disease
• D) Diuretics
Answer: A) Hemolysis during blood draw
Explanation: Potassium released from lysed cells in vitro falsely elevates serum potassium. It does not reflect true hyperkalemia. Correct handling prevents misdiagnosis and inappropriate treatment.

Hypophosphatemia affects:
• A) ATP production
• B) Muscle strength
• C) RBC function
• D) All of the above
Answer: D) All of the above
Explanation: Low phosphate impairs energy metabolism, leading to muscle weakness, hemolysis, respiratory failure, rhabdomyolysis, and neurological deficits. Causes include malnutrition, refeeding syndrome, alcohol, and phosphate-binding drugs.

Hyperphosphatemia in CKD leads to:
• A) Secondary hyperparathyroidism
• B) Vascular calcification
• C) Bone disease
• D) All of the above
Answer: D) All of the above
Explanation: Phosphate retention stimulates PTH secretion (secondary hyperparathyroidism), promotes vascular calcification, and leads to renal osteodystrophy. Management includes phosphate binders, diet control, and dialysis.

Hypochloremia is associated with:
• A) Vomiting
• B) Diuretic therapy
• C) Metabolic alkalosis
• D) All of the above
Answer: D) All of the above
Explanation: Loss of chloride occurs via vomiting, diuretics, or shifts during alkalosis. Hypochloremia contributes to volume depletion, alkalosis, and electrolyte disturbances such as hypokalemia.

Sodium imbalance primarily affects:
• A) Muscle contraction
• B) Neurological function
• C) Bone mineralization
• D) ATP production
Answer: B) Neurological function
Explanation: Sodium determines extracellular osmolality. Hyponatremia or hypernatremia leads to cerebral edema or dehydration, causing confusion, seizures, and coma. Muscle effects are secondary; bone mineralization and ATP are unaffected directly.