Extracellular potassium makes up about 2% of the total body potassium; the remaining 98% is intracellular.
total body potassium (in mEq) =
= (27.3 * (body weight in kgs)) + (11.5 * (body height in cm)) - (21.9 * (age in years) + 778
Levels of potassium depletion can be estimated from the serum potassium concentration. In a 70 kg person, a decrease in the serum potassium from 4 to 3 mEq/L represents a 300-400 mEq potassium deficit.
potassium deficit in mEq for 70 kg man =
= 1491.4497 - (379.0618 * (serum potassium in mEq/L))
In some situations such as diabetic ketoacidosis, the deficit estimates may be misleading due to shift of potassium from within to outside of cells (low intracellular potassium, normal to high extracellular potassium).
In addition, potassium levels are affected by the pH. When the pH increases by 0.1, the potassium decreases by about 0.6 mEq/L (mmol/L). In a patient with acidosis and hypokalemia, attempts to correct the acidosis will worsen the degree of hypokalemia.
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