Fluid and electrolyte analysis MCQs With Answer

This blog provides a focused collection of multiple-choice questions on fluid and electrolyte analysis tailored for M.Pharm students in Clinical Pharmacy Practice. Covering fundamentals and advanced concepts, the quiz emphasizes clinical interpretation, laboratory methods, specimen handling, and calculation-based problem solving relevant to patient care. Each question is designed to test conceptual clarity on sodium, potassium, chloride, bicarbonate, calcium, magnesium, phosphate, osmolality, anion gap, and fluid therapy choices. Detailed answer keys are provided to reinforce learning and prepare students for exams and clinical decision-making. Use this set to identify gaps, practice analytic reasoning, and strengthen applied knowledge in electrolyte management.

Q1. Which laboratory method is most commonly used for routine measurement of serum sodium in hospital clinical chemistry analyzers?

• Flame photometry
• Colorimetric assay
• Ion-selective electrode (ISE)
• Atomic absorption spectroscopy

Correct Answer: Ion-selective electrode (ISE)

Q2. A patient has serum Na+ 128 mmol/L, glucose 500 mg/dL (27.8 mmol/L). What is the approximate corrected serum sodium for hyperglycemia?

• 120 mmol/L
• 132 mmol/L
• 136 mmol/L
• 142 mmol/L

Correct Answer: 132 mmol/L

Q3. Which calculation gives the serum osmolality (mOsm/kg) most accurately in routine clinical practice?

• 2 × [Na+] + [K+] + glucose/18 + BUN/2.8
• 2 × ([Na+] + [K+] + [Cl-])
• [Na+] + [Cl-] + bicarbonate
• 2 × [Na+] + glucose/18 + BUN/2.8

Correct Answer: 2 × [Na+] + glucose/18 + BUN/2.8

Q4. An increased anion gap metabolic acidosis is most likely caused by which of the following?

• Diarrhea
• Renal tubular acidosis type II
• Lactic acidosis
• Hyperchloremia due to saline infusion

Correct Answer: Lactic acidosis

Q5. Which electrolyte change is most characteristic of primary hyperaldosteronism (Conn’s syndrome)?

• Hyponatremia with hyperkalemia
• Hypernatremia with hyperkalemia
• Hypernatremia with hypokalemia
• Hyponatremia with hypokalemia

Correct Answer: Hypernatremia with hypokalemia

Q6. Which fluid is isotonic and commonly recommended for initial resuscitation in hypovolemic shock?

• 0.9% sodium chloride (normal saline)
• 5% dextrose in water (D5W)
• 0.45% sodium chloride (half-normal saline)
• 3% sodium chloride

Correct Answer: 0.9% sodium chloride (normal saline)

Q7. In hyponatremia evaluation, a urine osmolality of 50 mOsm/kg suggests which mechanism?

• Syndrome of inappropriate ADH secretion (SIADH)
• Primary polydipsia or excessive free water intake
• Renal salt wasting
• Adrenal insufficiency

Correct Answer: Primary polydipsia or excessive free water intake

Q8. Which of the following best describes the principle of anion gap (AG) calculation?

• AG = [Na+] + [K+] – [Cl-] – [HCO3-]
• AG = [Na+] – ([Cl-] + [HCO3-])
• AG = [Cl-] + [HCO3-] – [Na+]
• AG = 2 × [Na+] – [Cl-]

Correct Answer: AG = [Na+] – ([Cl-] + [HCO3-])

Q9. Which laboratory artifact can cause a spuriously high serum potassium (pseudohyperkalemia)?

• Hemolysis of the blood sample
• Hypothermia of the sample
• Use of heparin as anticoagulant
• Collection in a fluoride tube

Correct Answer: Hemolysis of the blood sample

Q10. A low serum magnesium can cause which of the following electrolyte disturbances that is often refractory to correction without magnesium repletion?

• Hypernatremia
• Hypocalcemia
• Hyperkalemia
• Hyperchloremia

Correct Answer: Hypocalcemia

Q11. Which urine electrolyte test is most useful to differentiate renal from non-renal causes of hypokalemia?

• Urine osmolality
• Urine potassium-to-creatinine ratio
• Urine sodium concentration alone
• Urine magnesium concentration

Correct Answer: Urine potassium-to-creatinine ratio

Q12. Which acid-base disturbance is suggested by an arterial blood gas with pH 7.28, PaCO2 55 mmHg, HCO3- 24 mmol/L?

• Metabolic acidosis with respiratory compensation
• Respiratory acidosis with metabolic compensation
• Primary respiratory acidosis
• Metabolic alkalosis with respiratory compensation

Correct Answer: Primary respiratory acidosis

Q13. Measurement of serum ionized calcium is preferred over total calcium in which clinical scenario?

• When albumin concentration is significantly abnormal
• Routine population screening in healthy individuals
• Assessing calcium in mild dehydration only
• Estimating total body calcium stores

Correct Answer: When albumin concentration is significantly abnormal

Q14. Which of the following is the best description of tonicity?

• The total osmoles per liter of solution
• The effective osmotic pressure exerted by solutes that do not cross the membrane
• The concentration of electrolytes only
• The total body water divided by extracellular fluid volume

Correct Answer: The effective osmotic pressure exerted by solutes that do not cross the membrane

Q15. In the assessment of hyponatremia, a urine sodium >30 mmol/L with euvolemia most strongly suggests which diagnosis?

• Congestive heart failure
• Dehydration from gastrointestinal losses
• Syndrome of inappropriate ADH secretion (SIADH)
• Primary polydipsia

Correct Answer: Syndrome of inappropriate ADH secretion (SIADH)

Q16. During laboratory measurement, which pre-analytical factor most commonly causes falsely low plasma bicarbonate (HCO3-) values?

• Delayed separation of plasma and exposure to air (CO2 loss)
• Use of heparinized tubes
• Refrigeration of samples immediately after collection
• Collecting blood from a catheter with saline flush

Correct Answer: Delayed separation of plasma and exposure to air (CO2 loss)

Q17. Which electrolyte abnormality is most commonly associated with tumor lysis syndrome?

• Hypophosphatemia
• Hyperkalemia
• Hypokalemia
• Hypercalcemia

Correct Answer: Hyperkalemia

Q18. Which statement about fractional excretion of sodium (FENa) is correct?

• FENa <1% suggests intrinsic renal failure
• FENa >2% is typical of pre-renal azotemia
• FENa <1% usually indicates a pre-renal cause of AKI
• FENa is independent of diuretic use

Correct Answer: FENa <1% usually indicates a pre-renal cause of AKI

Q19. An increased serum chloride with normal sodium and low bicarbonate most likely indicates which acid–base disorder?

• High-anion-gap metabolic acidosis
• Hypochloremic metabolic alkalosis
• Normal-anion-gap (hyperchloremic) metabolic acidosis
• Respiratory alkalosis

Correct Answer: Normal-anion-gap (hyperchloremic) metabolic acidosis

Q20. Which laboratory technique is preferred for precise measurement of serum phosphate in critical care patients?

• Colorimetric molybdate method on automated analyzer
• Ion-selective electrode designed for phosphate
• Flame photometry
• Enzymatic glucose oxidase method

Correct Answer: Colorimetric molybdate method on automated analyzer

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