molecular weight of magnesium: 24.305
valence of magnesium ion: 2 (1 mmol = 2 mEq)
Patient selection: one or more risk factors for poor intake, poor absorption or increased loss
24 hour urine output for magnesium in mg =
= (magnesium concentration in mg/dL) * (24 hour urine output in mL) / 100
24 hour urine output for magnesium in mmol =
= (magnesium concentration in mmol/L) * (24 hour urine output in mL) / 1000
Interpretation:
• The lower limit of the normal reference range for magnesium excretion is 3 mmol/day (approximately 75 mg/day).
• A decreased urine output but normal or low normal magnesium reflects decreased total body stores.
• Low serum magnesium levels usually are associated with a urine excretion below 20-25 mg/day (0.82 - 1.03 mmol/day; see Figure 2, page 23)
