title: The utility and accuracy of four equations in predicting sodium levels in dysnatremic patients.
abstract: BACKGROUND
  Improper correction of hyponatremia can cause severe complications, including osmotic demyelination syndrome (ODS). The Adrogué-Madias equation (AM), the Barsoum-Levine (BL) equation, the Electrolyte Free Water Clearance (EFWC) equation and the Nguyen-Kurtz (NK) equation are four derived equations based on the empirically derived Edelman equation for predicting sodium at a later time (Na2) from a known starting sodium (Na1), fluid/electrolyte composition and input and output volumes.
  
  
  METHODS
  Our retrospective study included 43 data points from 31 mostly hyponatremic patients. We calculated Na2 based on five sets of rules that were progressively more precisely calculated. Sets A-D included all 31 patients and 43 data points and set E was based on 15 patients and 27 data points.
  
  
  RESULTS
  The root mean square error was calculated and found to be between 4.79 and 6.37 mmol/L (mEq/L) for all sets. Bland-Altman analysis showed high variability and discrepancies between the predicted and actual Na2.
  
  
  CONCLUSIONS
  Like similar studies in hypernatremic patients, the data suggest that hyponatremic modeling equations are not reliably accurate in predicting Na2 from Na1 and available clinical data regarding sodium, potassium and fluid balance over longer time frames (12-30 h). Our study was retrospective and was done in an inpatient setting and thus was subject to limitations and laboratory measurement variability, but showed that all four equations are not able to reliably predict Na2 from Na1 and inputs across a 12-30 h period.
authors.affiliation: Division of Nephrology, Department of Medicine , Cedars-Sinai Medical Center , 8700 Beverly Blvd, Los Angeles, CA , USA.
authors.forename: Ramy Magdy
authors.initials: RM
authors.lastname: Hanna
authors.affiliation: Division of Nephrology, Department of Medicine , Kaiser Permanente , Fontana, CA , USA.
authors.forename: Wan-Ting
authors.initials: WT
authors.lastname: Yang
authors.affiliation: Division of Nephrology, Department of Medicine , Kaiser Permanente , Panorama City, CA , USA.
authors.forename: Eduardo A
authors.initials: EA
authors.lastname: Lopez
authors.affiliation: Division of Nephrology, Department of Medicine , UCLA David Geffen School of Medicine , Los Angeles, CA , USA.
authors.forename: Joseph Nabil
authors.initials: JN
authors.lastname: Riad
authors.affiliation: Division of Nephrology, Department of Medicine , UCLA David Geffen School of Medicine , Los Angeles, CA , USA.
authors.forename: James
authors.initials: J
authors.lastname: Wilson
keywords: clearance; hyponatremia; intensive care; nutrition; vasopressin