AACN Essentials of Critical Care Nursing Practice Test 2026 – Your Comprehensive All-in-One Resource for Exam Success!

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Which formula represents the anion gap as described in the material?

(Na+ + Cl-) - (K+ + HCO3-)

Na+ - (Cl- + HCO3-)

(Na+ + K+) - (Cl- + HCO3-)

Anion gap reflects unmeasured anions in the blood by balancing the electrical charges of measured ions. The main measured cations are sodium and potassium, and the main measured anions are chloride and bicarbonate. So the gap is calculated as (Na+ + K+) - (Cl- + HCO3-). This value estimates the unmeasured anions, which helps interpret metabolic acidosis and distinguish its causes. Some settings omit potassium, giving Na+ - (Cl- + HCO3-), but the description here uses both Na and K, making (Na+ + K+) - (Cl- + HCO3-) the correct formula.

(Na+ + K+) + (Cl- + HCO3-)