The Usefulness of Measuring the Anion Gap in Diagnosing Metformin-associated Lactic Acidosis

A Case Series

Jesus Ruiz-Ramos; Laura Lozano-Polo; Ana Juanes-Borrego; Iván Agra-Montava; Mireia Puig-Campmany; María Antonia Mangues-Bafalluy


J Med Case Reports. 2021;15(17) 

In This Article


Since the 1950s, metformin has been successfully used as a first-line pharmacotherapy for treating individuals with type II diabetes.[1] Although it is considered as a drug with a broad safety profile, metformin-associated lactic acidosis (MALA) is a widely documented adverse event.[2,3] MALA is a rare condition associated with poor prognoses and has an estimated mortality of between 25 and 50%.[4] It develops more frequently in elderly patients with impaired kidney function and liver failure[5]

It has been established that a pH bellow 7.35, a high lactate level, and compatible symptomatology are key elements in detecting the presence of MALA.[5] The anion gap, which measure the difference between cations and anions in serum, is an useful tool when attempting to identify the cause of metabolic acidosis. Despite a high anion gap being considered one of the main causes of metabolic acidosis, it is still uncertain whether there is an association between an anion gap and MALA diagnosis. In this report, we present a case series of suspected MALA patients with the aim of highlighting the importance of the anion gap value in MALA diagnoses.