Hypomagnesemia is having a serum magnesium concentration of <1.3 mEq/L.
Patients with mild hypomagnesemia is asymptomatic and have usually a serum Mg >0.5 mmol/L. While those with moderate-severe hypomagnesemia, the patient is symptomatic and have serum Mg <5 mmol/L.
Hypermagnesemia signs and symptoms usually do not appear unless Mg >2 mmol/L (5 mg/dL). It rarely occurs and usually iatrogenic.