Routine plasma magnesium estimation: a useful test?

An investigation of 527 consecutive patients showed that 24 (4.5%) had hypomagnesaemia (plasma magnesium level, less than 0.70 mmol/L) and 26 (4.9%) had hypermagnesaemia (plasma magnesium level, greater than 1.00 mmol/L). The magnesium levels returned to normal values without specific treatment in 15 of the hypomagnesaemic patients. Magnesium levels of less than 0.60 mmol/L occurred only in patients with disorders that are known to cause magnesium deficiency. Seventeen of the hypermagnesaemic patients had plasma creatinine values in excess of 0.20 mmol/L; in the remainder, the plasma magnesium level was less than 1.10 mmol/L. Eighteen of the hypermagnesaemic patients received no specific treatment, in five the plasma magnesium values returned to normal levels within three days, while the high levels were maintained in the remaining 13 patients, but none was in excess of 1.15 mmol/L. These results suggest that many cases of hypomagnesaemia are transient and do not require treatment; severe hypomagnesaemia occurs only in patients with disorders that are known to cause magnesium deficiency; hypermagnesaemia is common in renal insufficiency; most cases of mild hypermagnesaemia (plasma magnesium level, less than 1.20 mmol/L) do not require specific treatment; and that screening all patients for hyper- or hypomagnesaemia is clinically unproductive and only those patients with disorders that are known to affect magnesium metabolism need to be investigated.