Hypomagnesemia (or hypomagnesaemia) is an electrolyte disturbance in which there is an abnormally low level of magnesium in the blood. Normal magnesium levels in humans fall between 1.7 - 2.2 mg/dL. Usually a serum level less than 1.7 mg/dL (0.7 mmol/L) is used as reference for hypomagnesemia (not hypomagnesia which refers to low magnesium content in food/supplement sources). The prefix hypo- means under (contrast with hyper-, meaning over). The root 'magnes' refers to magnesium. The suffix of the word, -emia, means 'in the blood.'