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Kidney Week

Abstract: PO1118

Selection of the Best Equation for Serum Osmolality Calculation in Hemodialysis Patients

Session Information

Category: Dialysis

  • 701 Dialysis: Hemodialysis and Frequent Dialysis

Authors

  • Miyagi, Tsuyoshi, Harold Simmons Center for Kidney Disease Research and Epidemiology, Orange, California, United States
  • Wenziger, Cachet, Harold Simmons Center for Kidney Disease Research and Epidemiology, Orange, California, United States
  • Narasaki, Yoko, Harold Simmons Center for Kidney Disease Research and Epidemiology, Orange, California, United States
  • Miyasato, Yoshikazu, Harold Simmons Center for Kidney Disease Research and Epidemiology, Orange, California, United States
  • Kimura, Hiroshi, Harold Simmons Center for Kidney Disease Research and Epidemiology, Orange, California, United States
  • Iseki, Kunitoshi, Ryukyu Daigaku Igakubu Daigakuin Igaku Kenkyuka, Nakagami-gun, Okinawa, Japan
  • Tantisattamo, Ekamol, Harold Simmons Center for Kidney Disease Research and Epidemiology, Orange, California, United States
  • Rhee, Connie, Harold Simmons Center for Kidney Disease Research and Epidemiology, Orange, California, United States
  • Streja, Elani, Harold Simmons Center for Kidney Disease Research and Epidemiology, Orange, California, United States
  • Kalantar-Zadeh, Kamyar, Harold Simmons Center for Kidney Disease Research and Epidemiology, Orange, California, United States
Background

Although the serum osmolality (SOsm) is determined by circulating solutes including sodium, potassium, glucose and urea, calculated serum osmolality formula without potassium (2[Na, in mmol/L] + [Glucose, in mg/dL] / 18 + [BUN in mg/dL] / 2.8) is commonly used. Several different equations have been previously described to estimate SOsm. Although in hemodialysis patients it is important to monitor homeostasis by means of estimating SOsm, few studies have examined the accuracy of those equations.

Methods

We identified 20 patients who transitioned to hemodialysis therapy and had repeated SOsm data along with, pre-dialysis sodium, potassium, glucose, and blood urea nitrogen (BUN) on the same day. We compared estimated SOsm by the 13 equations used in the previous literature and measured SOsm.

Results

The patients were 52% male, 33% non-white, and the mean age was 60 ± 17 (mean± SD) years. There were 65 measured SOsm and the mean (± SD) was 310.8 ± 12.0 mOsm/Kg. The following equation provided the best fit between measured and calculated SOsm: 2([Na, in mmol/L] + [K, in mmol/L]) + [Glucose, in mg/dL] / 18 + [BUN in mg/dL] / 2.8 (mean difference, -0.7 mOsm/Kg; 95% confidence interval, -2.12–0.71; P=0.32).

Conclusion

Our result suggests that the equation for estimating serum osmolality in hemodialysis patients should include serum potassium in addition to other components usually used to estimate serum osmolality in non-hemodialysis patient.