title: Do intracellular, extracellular or urinary magnesium concentrations predict renal retention of magnesium in critically ill patients?
abstract: OBJECTIVE
  Magnesium disorders are common in hospitalized patients. In patients with low or normal magnesium, the intravenous magnesium loading test has been demonstrated to be a sensitive test to assess magnesium deficiency in critically ill patients. However, it is more time consuming and more difficult than the measurement of intracellular or extracellular magnesium concentrations. This study evaluated whether erythrocyte, plasma and urinary magnesium concentrations predict renal magnesium retention measured by th magnesium loading test.
  
  
  METHODS
  One-hundred-and-three intensive care patients (36 females, 67 males) in a tertiary care centre and 41 healthy subjects (13 females, 28 males) took part in this prospective study. Intracellular, total plasma, ionize extracellular and urinary magnesium concentrations were measured and also magnesium retention by intravenous magnesium loading test.
  
  
  RESULTS
  Total plasma magnesium concentration was poorly correlated with magnesium retention (r = 0.36 r2 = 0.13) and was the only parameter that significantly predicted magnesium retention in intensive care patients (P < 0.01). However, only 10% of the magnesium retention data were linked to the total plasma magnesium concentration.
  
  
  CONCLUSIONS
  Total plasma magnesium concentration predicts magnesium retention in critically ill intensive care patients but not intracellular and urinary magnesium concentrations. Only a small proportion of the magnesium retention was due to the total plasma magnesium concentration.
authors.affiliation: Georg-August-University of Goettingen, Department of Anesthesiology, Emergency- and Intensive-Care-Medicine, Goettingen, Germany. psaur@gwdg.de
authors.forename: P
authors.initials: P
authors.lastname: Saur
authors.forename: P D
authors.initials: PD
authors.lastname: Niedmann
authors.forename: E
authors.initials: E
authors.lastname: Brunner
authors.forename: D
authors.initials: D
authors.lastname: Kettler
mesh_terms: D003422:Critical Care; D016638:Critical Illness; D004912:Erythrocytes / Q000737:chemistry; D005110:Extracellular Space / Q000378:metabolism*; D005260:Female; D006801:Humans; D007424:Intracellular Fluid / Q000378:metabolism*; D007668:Kidney / Q000378:metabolism*; D008274:Magnesium / Q000097:blood / Q000378:metabolism* / Q000652:urine; D008275:Magnesium Deficiency / Q000097:blood / Q000175:diagnosis / Q000652:urine; D008297:Male; D008875:Middle Aged; D011153:Population; D011237:Predictive Value of Tests
chemical_list: D008274:Magnesium