Acid-Base, Fluid and Electrolyte Biochemistry MCQs

Biochemistry · 36 free questions with answers & explanations.

  1. A patient has pH 7.28, PaCO2 28 mmHg, and HCO3⁻ 12 mEq/L. Using Winter's formula for respiratory compensation in metabolic acidosis (expected PaCO2 = 1.5×[HCO3⁻] + 8 ± 2), what conclusion can be drawn?
  2. The Henderson-Hasselbalch equation for the bicarbonate buffer system is pH = pKa + log([HCO3⁻]/[H2CO3]). In blood at physiologic pH 7.4, the ratio of [HCO3⁻] to [H2CO3] is approximately:
  3. In proximal renal tubular acidosis (type 2 RTA), the primary biochemical defect is failure of bicarbonate reabsorption in the proximal tubule. Which transporter is principally responsible for basolateral HCO3⁻ exit from the proximal tubular cell?
  4. An ABG shows pH 7.52, PaCO2 48 mmHg, HCO3- 38 mEq/L. The primary disorder and compensatory response are:
  5. The Henderson-Hasselbalch equation underlies blood pH regulation. At physiological pH of 7.40, what is the ratio of bicarbonate to dissolved CO2 (HCO3-:dCO2) assuming pKa of carbonic acid = 6.1?
  6. Proximal renal tubular acidosis (type 2 RTA) is characterised by defective HCO3- reabsorption in the PCT. This directly impairs which transport mechanism?
  7. A 25-year-old woman with anorexia nervosa and self-induced vomiting has ABG: pH 7.52, PaCO2 48 mmHg, HCO3− 38 mEq/L. Which acid-base disturbance is present and what is the mechanism?
  8. In type 1 renal tubular acidosis (distal RTA), the underlying defect is failure of H+ secretion in the collecting duct. The characteristic biochemical finding that distinguishes it from other causes of non-anion-gap metabolic acidosis is:
  9. The Henderson-Hasselbalch equation for the bicarbonate buffer system is pH = 6.1 + log([HCO3−] / 0.03 × PaCO2). At normal values (HCO3− = 24 mEq/L, PaCO2 = 40 mmHg), the ratio [HCO3−]/[H2CO3] is approximately:
  10. A patient's arterial blood gas shows pH 7.28, PaCO2 28 mmHg, HCO3− 13 mEq/L. Which is the PRIMARY acid-base disorder and the appropriate compensatory response?
  11. The bicarbonate buffer system is the principal extracellular buffer. The Henderson-Hasselbalch equation for this system is pH = pKa + log([HCO3−]/[H2CO3]). The normal ratio of [HCO3−]/[H2CO3] maintained at pH 7.4 is approximately:
  12. A patient with chronic diarrhea develops hyperchloremic metabolic acidosis with normal anion gap. What is the BIOCHEMICAL explanation for the normal anion gap?
  13. A 60-year-old diabetic is admitted with an arterial blood gas showing: pH 7.22, PaCO2 20 mmHg, HCO3- 8 mEq/L, Na+ 138, Cl- 100, glucose 180 mg/dL. Serum lactate is normal; urine ketones are negative. What is the MOST likely acid-base disorder and its cause?
  14. The Henderson-Hasselbalch equation for the bicarbonate buffer system is pH = pKa + log [HCO3-]/[H2CO3]. The pKa of this system is approximately 6.1. At normal blood pH of 7.4, the HCO3-:H2CO3 ratio is approximately:
  15. In Type 1 (distal) Renal Tubular Acidosis (dRTA), the patient cannot acidify the urine below pH 5.5 despite systemic acidosis. Serum electrolytes show hyperchloraemia and hypokalaemia. The biochemical defect responsible for hypokalaemia in dRTA is:
  16. A patient with chronic renal failure has the following ABG: pH 7.30, PaCO2 28 mmHg, HCO3- 13 mEq/L, Na 138, Cl 105. Calculated anion gap = 20 mEq/L (high). Expected respiratory compensation for metabolic acidosis using Winters formula is PaCO2 = 1.5 × HCO3- + 8 ± 2. Expected PaCO2 = 27.5 ± 2. The actual PaCO2 is 28 mmHg. This means:
  17. In distal renal tubular acidosis (Type 1 RTA), the defect is failure of the collecting duct to secrete H+ ions. The biochemical consequence that distinguishes Type 1 from Type 2 RTA on urine pH measurement is:
  18. The Henderson-Hasselbalch equation for the bicarbonate buffer system is pH = 6.1 + log [HCO3-]/[H2CO3]. In clinical practice, carbonic acid concentration [H2CO3] is replaced by 0.03 × PaCO2. The factor 0.03 represents:
  19. A 25-year-old with type 1 diabetes presents with Kussmaul breathing, blood glucose 480 mg/dL, pH 7.1, bicarbonate 8 mEq/L. The primary biochemical mechanism generating this metabolic acidosis is:
  20. The Henderson-Hasselbalch equation describes the relationship between pH and bicarbonate. In a patient with metabolic alkalosis, compensatory hypoventilation is limited. What is the ceiling PaCO2 in respiratory compensation for metabolic alkalosis?
  21. The Na⁺-K⁺-ATPase pump maintains the resting membrane potential. Which statement correctly describes the stoichiometry and energy cost of this pump?
  22. A patient has pH 7.28, PaCO2 58 mmHg, HCO3- 26 mEq/L. The expected compensation for this primary respiratory acidosis and the adequacy of the measured HCO3- can be assessed by the rule that chronic respiratory acidosis raises HCO3- by:
  23. The anion gap (AG) is calculated as Na+ - (Cl- + HCO3-). A patient has Na+ 138, Cl- 102, HCO3- 14, serum albumin 2 g/dL (normal 4 g/dL). The corrected anion gap reveals which type of metabolic acidosis?
  24. Renal tubular acidosis type I (distal RTA) is characterised by inability to acidify urine below pH 5.5. The enzyme whose deficiency in the alpha-intercalated cells of the collecting duct directly causes this defect is:
  25. The Henderson-Hasselbalch equation for blood pH is: pH = 6.1 + log([HCO3−] / 0.03 × pCO2). A patient has pH 7.20, pCO2 60 mmHg, and HCO3− 22 mEq/L. What is the primary acid-base disorder?
  26. Carbonic anhydrase II deficiency causes a rare syndrome of renal tubular acidosis, osteopetrosis, and cerebral calcification. The enzyme normally accelerates which reaction that is essential for urinary H+ secretion?
  27. In diabetic ketoacidosis, the anion gap is elevated because of accumulation of ketoacid anions. The anion gap is calculated as Na+ − (Cl− + HCO3−). A patient has Na+ 140, Cl− 112, HCO3− 8 mEq/L. What is the anion gap and what does a simultaneous delta ratio (delta gap / delta bicarbonate) of 0.5 suggest?
  28. Lactic acidosis type A results from tissue hypoperfusion. In the anaerobic state, pyruvate accepts electrons from NADH via lactate dehydrogenase (LDH) to form lactate, regenerating NAD+. Why is NAD+ regeneration critical here?
  29. A 22-year-old with type 1 diabetes presents with vomiting and altered consciousness. Blood gas: pH 7.10, PaCO2 18 mmHg, HCO3- 5 mEq/L, Na+ 138, Cl- 100, K+ 5.2 mEq/L. The anion gap is:
  30. A 50-year-old COPD patient on home oxygen has: pH 7.36, PaCO2 58 mmHg, HCO3- 32 mEq/L. This blood gas pattern represents:
  31. The delta-delta ratio (delta AG / delta HCO3-) is used to detect a concurrent metabolic alkalosis in a high anion gap metabolic acidosis. A delta-delta ratio >2 suggests:
  32. Distal renal tubular acidosis (Type 1 RTA) is characterised by all of the following EXCEPT:
  33. A 28-year-old woman with type 1 diabetes presents obtunded. ABG: pH 7.22, PaCO2 18 mmHg, HCO3- 7 mEq/L. Na+ 138, Cl- 98 mEq/L. Calculate the anion gap and delta ratio.
  34. A 70-year-old with COPD has ABG: pH 7.36, PaCO2 58 mmHg, HCO3- 32 mEq/L. This pattern represents:
  35. A patient with profuse vomiting develops metabolic alkalosis. Which renal mechanism PARADOXICALLY perpetuates alkalosis by excreting acid urine?
  36. Henderson-Hasselbalch equation for bicarbonate buffer: pH = 6.1 + log([HCO3-] / 0.03 × PaCO2). If HCO3- = 12 mEq/L and PaCO2 = 24 mmHg, what is the approximate pH?
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