What are the causes of low potassium (hypokalemia)?

See below. A low potassium level has many causes, some are due to decreased intake, some due to increase loss from the skin, gut eg loose stools, urine eg alcohol intake, tubular problems or magnesium deficiency.Others are due to shift of potassium into the cells.
In/out/shift. The approach is as follows: 1. Not enough in: this is not likely 2. Too much out: a) urine: can occur with diuretics, low magnesium b) gi: as a result of vomittng, or due to diarrhea 3. Shift: into cells in patients with alkalosis, or with Insulin excess.