Hypomagnesaemia

What it is

Hypomagnesemia is a low magnesium level. It matters less for itself than for what comes with it: a hypokalemia that will not correct until the low Mg2+ is corrected, and a hypocalcemia that goes with it, since severe hypomagnesemia causes decreased PTH release and resistance to PTH. In an alcoholic patient it is the electrolyte abnormality that is typically the cause of hypocalcemia, and the likely underlying cause of refractory hypokalemia.

Causes and risk

• Gitelman syndrome, an autosomal recessive defect of the Na+/Cl- cotransporter (NCC) in the distal convoluted tubule. Magnesium is significantly low, with low K+, metabolic alkalosis, low Ca2+ excretion (hypocalciuria) and a normal or low blood pressure. Bartter syndrome, by contrast, sits in the thick ascending limb of the loop of Henle at the Na+/K+/2Cl- cotransporter (NKCC2), where magnesium is normal or only slightly low and calcium excretion is high (hypercalciuria).
• Long-term use of proton pump inhibitors (PPIs), which is also associated with fractures, vitamin B 12 deficiency, iron deficiency and acute interstitial nephritis with progression to chronic kidney disease.
• Alcohol. In an alcoholic patient, hypomagnesemia is the likely underlying cause of refractory hypokalemia, and severe hypomagnesemia is the cause of the hypocalcemia as well.
• The neonate of a pregnancy with GDM, where hypomagnesemia is listed with hypoglycemia and hypocalcemia among the neonatal complications.