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352) A patient has the laboratory results shown in the table.

Patient Reference Range Units

Na 141 136–146 mmol/L

K 4.0 3.5–5.0 mmol/L

Cl 88 101–109 mmol/L

CO₂ 48 22–29 mmol/L

pH 7.48 7.36–7.41

PCO₂ 47 32–45 mmHg

Which one of the following is the most likely cause of these results?

	Patient	Reference Range	Units
Na	141	136–146	mmol/L
K	4.0	3.5–5.0	mmol/L
Cl	88	101–109	mmol/L
CO₂	48	22–29	mmol/L
pH	7.48	7.36–7.41
PCO₂	47	32–45	mmHg

Metabolic acidosis. Respiratory acidosis. Metabolic alkalosis. Diabetic ketoacidosis (DKA). Respiratory alkalosis.

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• Metabolic alkalosis can result, for example, from ingestion of large amounts of alkali antacids or aggressive intravenous treatment with bicarbonate solutions. Loss of gastric hydrochloric acid from the stomach caused by severe vomiting, or aspiration of gastric fluids, can also result in metabolic alkalosis.

• Hypovolemia (e.g., from severe vomiting) will result in reabsorption of Na⁺ to restore volume, and the renal retention of HCO₃^– in the presence of low chloride concentrations to maintain electrical neutrality. The decrease of chloride in metabolic alkalosis is known as hypochloremic alkalosis.

• In addition, K⁺ and H⁺ are excreted in exchange for Na⁺, which will increase the blood pH. The urine pH may be acidic in metabolic alkalosis.

• The anion gap is the difference between the measured cations and the measured anions. The anion gap is calculated as: [measured cations (Na + K)] – [measured anions (Cl + HCO₃^–)]. The reference range is usually 7 to 16 mmol/L. In the case in this question, the anion gap was 9 mmol/L. A normal anion gap is usually observed in metabolic alkalosis.

• In metabolic alkalosis, HCO₃^– is increased, PCO₂ is normal or slightly increased, and the HCO₃^–/0.03 PCO₂ ratio, which is used in the Henderson-Hasselbalch equation to calculate the pH, is increased, which causes the elevated blood pH.

Park SH, An D, Chang YJ, et al: Development and validation of an arterial blood gas analysis interpretation algorithm for application in clinical laboratory service. Ann Clin Biochem 2011;48:130–135.

Hood JL, Scott MG: Physiology and disorders of water, electrolyte and acid-base metabolism.In: Burtis CA, Ashwood ER, Bruns DE, eds. Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. 5th ed. St. Louis: Elsevier Saunders, 2012:1609–1635.

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Clinical Pathology: General Principles, Clinical Chemistry

352) A patient has the laboratory results shown in the table. Patient Reference Range Units Na 141 136–146 mmol/L K 4.0 3.5–5.0 mmol/L Cl 88 101–109 mmol/L CO2 48 22–29 mmol/L pH 7.48 7.36–7.41 PCO2 47 32–45 mmHg Which one of the following is the most likely cause of these results?

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