Potential serum magnesium under request in primary care. Laboratory interventions to identify patients with hypomagnesemia

Magnesium is an important electrolyte for many cell functions as it is involved in more than 600 enzymatic reactions [1]. Hypomagnesemia is relatively common and often associated with hypocalcemia and hypokalemia [2]. Hypomagnesemia is a negative outcome predictor for cardiovascular and renal disorders [3] and has been implicated in the pathogenesis of hypertension [4]. There is an overall prevalence of hypomagnesemia of around 30% in patients with diabetes [5]. Magnesium should be assessed in many relevant clinical conditions such as arrhythmia, hypokalemia, hypocalcemia, diarrhea and chronic alcoholism and in critically ill patients and those on drugs known to cause hypomagnesemia. Despite its importance, however, this marker is often known as the forgotten cation, and many cases of hypomagnesemia remain undiagnosed. We hypothesized that – given asymptomatic magnesium depletion is often associated with hypokalemia and hypocalcemia, diabetes and hypertension – hypomagnesemia could be detected by measuring serum magnesium test in the above situations [6, 7]. We also hypothesized that the elderly population – likely to have more comorbidity – would be more prone to magnesium deficiency. Our laboratory is located at the public University Hospital of San Juan (Alicante, Spain), a 370-bed suburban community hospital that serves a population of 234,551 inhabitants, including nine different primary care centers. Laboratory requests are made through an electronic system that includes a field regarding the reason for the laboratory request by means of the International Classification of Diseases, Ninth Revision, Clinical Modification (CIE-9-MC) codes [8]. First, we evaluated the GPs’ request pattern for serum magnesium from January 2017 to August 2019, to study the demand for serum magnesium in primary care. After that, two cross-sectional studies were designed: one involving calcium and potassium for the same period as above and another one regarding diabetes, hypertension and elderly from March 1, 2019 to May 31, 2019. In consensus with GPs, we decided that the laboratory information system (LIS) would automatically add serum magnesium order (if it had not been requested by GPs) when calcium <7.5 mg/dL (1.9 mmol/L) or potassium <2.5 mEq/L (2.5 mmol/L). In a second meeting, we decided to screen for hypomagnesemia in primary care patients with diabetes (ICD-9: 250.0), hypertension (ICD-9: 401.0) and those older than 65 years living at home and institutionalized. The LIS would automatically register a serum magnesium order in such cases, to be measured on the original blood sample. In both strategies, an automatic comment is added in case the magnesium is low: “Patient with hypomagnesemia”. For all requests where magnesium test was automatically registered, we collected the patients’ *Corresponding author: Maria Salinas, PhD, Clinical Laboratory, Hospital Universitario de San Juan, Carretera Alicante-Valencia, s/n, 03550 San Juan de Alicante, Alicante, Spain; and Department of Biochemistry and Molecular Pathology, Universidad Miguel Hernandez, Elche, Spain, Phone: +34 965169463, Fax: +34 965169460, E-mail: salinas_mar@gva.es Emilio Flores: Clinical Laboratory, Hospital Universitario de San Juan, Carretera Alicante-Valencia, s/n, Alicante, Spain; and Department of Clinical Medicine, Universidad Miguel Hernandez, Elche, Spain Maite López-Garrigós and Rosa Carbonell: Clinical Laboratory, Hospital Universitario de San Juan, Carretera Alicante-Valencia, s/n, Alicante, Spain Francisco Pomares: Department of Endocrinology and Nutrition, Hospital Universitario de San Juan, San Juan de Alicante, Spain Carlos Leiva-Salinas: Department of Radiology, University of Missouri, Columbia, MO, USA Clin Chem Lab Med 2020; 58(10): e221–e223