Electrolytes are the high valence molecular ions in the bloodstream and other body fluids that help regulate body functions such as nerve transmission and osmotic fluid transfer. Sodium and potassium are the two most important electrolytes, but there are others. Sports drinks contain small but sufficient quantities of these electrolytes as sweating and exercise can cause an electrolyte imbalance even in a well hydrated person. Such imbalances can also be caused by severe diarrhea, severe vomiting and poor diet. In a hospital setting, a banana bag contains a mixture of electrolytes in the same quantities as the ideal mix in human blood. Electrolytes are routinely tested for as part of standard blood tests.
In Histories, House suspects an electrolyte imbalance when he finds the patient's vomit is salty.