Investigative algorithms for disorders affecting plasma magnesium: a narrative review

Abstract

Background and Objective: The following article is a part of a special series to aid the reader in diagnosing the cause of various electrolyte imbalances. By the end of the article, the reader will be able to order and interpret appropriate investigations when faced with a patient with low or high magnesium. Methods: A narrative, focused literature review was performed using PubMed, OMIM and Google during September 2021 to January 2022 to identify references published from database inception to January 2022. Reference lists from identified articles were also used. Language was restricted to English. Key Content and Findings: Magnesium is primarily intracellular with homeostasis tightly controlled via regulated gastrointestinal and renal absorption. It should be noted that in acutely ill people, hypomagnesaemia is more likely to be an epiphenomenon rather than representing a true magnesium deficiency—which takes months to years to develop (with plasma concentration maintained). If hypomagnesaemia is identified screen for gastrointestinal diseases or problem drinking and consider a 24-h urine collection to establish renal handling. For hypermagnesaemia consider drugs and tissue lysis. Conclusions: Diagnostic schema will be presented and the limitations of the laboratory tests discussed. The following schema, by focusing on the investigation of hypomagnesaemia and hypermagnesaemia, should support healthcare professionals to efficiently and systematically approach people with these electrolyte abnormalities.