Potassium levels may sometimes appear to be normal in blood tests when in fact there is a potassium deficiency in the body. Dr D Polzin states in
Chronic kidney disease (2007)
Delaware Valley Academy of Veterinary Medicine "muscle potassium content decreased in normokalemic cats with spontaneous CKD, indicating that a total-body deficit of potassium may develop well before the onset of hypokalemia." This is because, although potassium is used in the body's cells, the regulatory mechanism of the body is actually set to maintain a certain level of potassium in the blood, not the cells. Thus, when potassium levels drop, as they tend to do in early stage CKD, the cat's body will try to maintain levels of potassium in the blood by taking potassium from the cells. This means that at the intra-cellular level where the potassium is really needed, potassium levels are too low, even though the blood levels of potassium may appear to be normal.
There are a number of tests available for humans to test potassium at the intracellular level. One is the
Exa Test, which requires a buccal sample (from the cheek inside the mouth). I only know of one person who has had potassium checked at the intracellular level, but unfortunately he cannot remember which company his vet used.
Goal for Potassium Level in Bloodwork
Potassium is usually measured in either mEq/l (USA) or mmol/l (international). However, in practice the numbers are the same value for potassium, e.g. 4 mEq/l is the same as 4 mmol/l.
Although laboratories vary, most have a range around 3.5 to 5.5. Ideally though, you
want your cat's potassium level to be firmly in the middle, at around 4.4, but definitely above 4.