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Abstract: SA-PO732

Use of Serum Osmolality to Guide Management of Severe Hyponatremia Outside of Detectable Range

Session Information

Category: Fluid, Electrolytes, and Acid-Base Disorders

  • 1102 Fluid, Electrolyte, and Acid-Base Disorders: Clinical


  • Assante, William Joseph, Westchester Medical Center, Valhalla, New York, United States
  • Gupta, Sanjeev, Westchester Medical Center, Valhalla, New York, United States
  • Mittal, Amol, Westchester Medical Center, Valhalla, New York, United States
  • Chugh, Savneek S., Westchester Medical Center, Valhalla, New York, United States

Hyponatremia is common, and it is heterogeneous in its clinical presentation (ranging from mild and asymptomatic to critically low with severe symptoms, such as seizures). Competent management entails identifying the etiology and monitoring sodium closely to avoid overcorrection. Consequently, a challenge arises when the serum sodium is below measurable range for the lab. In such cases, it is more difficult to discern the starting sodium and therefore prevent overcorrection.This case demonstrates use of serum osmolality to estimate sodium in these cases.

Case Description

A 44-year-old male with a history of alcohol abuse was admitted to the hospital due to decompensated cirrhosis. He presented with jaundice, shortness of breath, and swelling in his lower extremities. Sodium on admission was < 106mg/dL, which is lower than the lower limit of calculation for the laboratory. Serum osmolality 219 mOsm/kg, urine Na <20 mmol/L, urine Cl <20 mmol/L, urine osmolality 413, BUN/Cr 7/0.66, serum alcohol level 113.7mg/dL.

Despite receiving 3% hypertonic saline for 24 hours, his sodium continued to be below 106mg/dL, even on blood gas analysis. In order to determine the initial sodium level upon admission and the rate of correction, we used the following formula: serum osmolality = 2(Na) + BUN/2.8 + Glucose/18 + EtOH/3.7 (where 219 = 2x Na + other values). According to this formula, the estimated initial sodium level was 94 mg/dL, and subsequent measurements using this formula showed appropriate correction. The patient remained on 3% hypertonic saline for 48 hours, and two days later, his sodium level reached 107.

At this point, the administration of 3% saline was discontinued, and the patient was given intravenous Lasix on a daily basis due to suspected hypervolemic hyponatremia in the context of liver cirrhosis. The sodium levels continued to improve slowly, reaching 140 on the eighth day of hospitalization.


The patient in this case presented with critically low sodium below detectable range and severe symptoms, necessitating a precise plan of care for improving sodium promptly but also without overcorrecting. Using simple algebraic calculations involving the serum osmolality formula, the patient's sodium was reliably estimated. This guided sodium correction without any episodes of overcorrection in this already critically ill patient.