Final answer:
It is false that an arterial blood sample is the most accurate measurement of the body's potassium; potassium is mainly intracellular, and serum levels do not reflect total body stores.
Step-by-step explanation:
The statement that the most accurate measurement of the body's store of potassium is an arterial blood sample is false.
Serum potassium levels, which are typically measured through blood tests, do not necessarily reflect total body potassium stores, as potassium is the major intracellular cation and its concentration is much higher inside cells than in the bloodstream or extracellular fluid.
The intracellular concentration of potassium is maintained by the sodium-potassium pumps in cell membranes, which actively transport potassium into and sodium out of cells.
Therefore, an arterial blood sample provides information about the level of serum potassium, not the total potassium stored in the body.