Question

The anion gap, an estimate of anions not directly measured in serum, is correctly calculated by which of the following formulae?

a) Anion Gap = (Na+ - Cl-) - HCO3-
b) Anion Gap = Na+ + K+ - Cl-
c) Anion Gap = HCO3- - (Na+ + K+)
d) Anion Gap = (Na+ + K+) - Cl-

Answer 1

The correct way to calculate the anion gap is by using the formula Anion Gap = (Na+ + K+) - (Cl- + HCO3-) or the simplified Anion Gap = Na+ - (Cl- + HCO3-) when potassium is omitted. This value is used to identify acid-base disturbances in the blood.

Step-by-step explanation:

The anion gap is a value calculated from serum electrolyte measurements, reflecting the concentration of unmeasured anions in the plasma. The correct formula to calculate the anion gap is Anion Gap = (Na+ + K+) - (Cl- + HCO3-), which represents the difference between the measured cations (sodium and potassium) and the measured anions (chloride and bicarbonate). Despite the sodium ion (Na+) being an inert cation that does not affect the pH of the solution, it is still accounted for in the anion gap calculation. Potassium (K+) is sometimes omitted from the calculation, simplifying the formula to Anion Gap = Na+ - (Cl- + HCO3-). This measure is important in identifying various acid-base disturbances and helping to narrow down potential differential diagnoses.