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Abstract: PO1155

Polyethylene Glycol-Induced Pseudohyponatremia

Session Information

Category: Fluid, Electrolyte, and Acid-Base Disorders

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

Authors

  • Reddy, Swetha, Mayo Clinic Arizona, Scottsdale, Arizona, United States
  • Swaminathan, Sundararaman, Mayo Clinic Arizona, Scottsdale, Arizona, United States
Introduction

Pseudohyponatremia due to Polyethylene glycol (PEG) is poorly described and goes unrecognized. We describe a case of hyperosmolar hyponatremia due to PEG absorption into the systemic circulation.

Case Description

An 84-year-old lady with hypertension and CKD stage 4 was admitted with an asymptomatic serum sodium of 121. Initially thought be due to SIADH. She was started on 1-liter fluid restriction, sodium chloride tablet and torsemide. Nephrology was consulted on day 3 as her serum creatinine was 2.9 (baseline 2.3 mg/dl) and sodium improved to only 124. Patient complained of increased thirst and had dry mucus membrane on examination. Labs on admission revealed a serum sodium of 121 mEq/L, a serum osmolality of 286 mOsm/kg, urine osmolality of 230 mOsm/kg and urine sodium of 40. Serum creatinine was 2.3 mg/dL, BUN 50 mg/dL, glucose of 100mg/dl, uric acid 8.1 mg/dL. Thyroid function tests and cortisol were within normal range. An osmolar gap of 22 was noted. In the absence of hyperglycemia and other potential causes of an osmotic gap, such as mannitol or alcohols, a careful review of medication showed that she was on 3 weeks of PEG for constipation. PEG was held, fluid restriction and torsemide discontinued. Resolution of osmolar gap was confirmed in two weeks with return in sodium to 134 and creatinine to 2.3.

Discussion

The prevalence of hyponatremia is reported at 7% in bowel prep patients. Etiology in these cases was due to increased free water intake. Hyperosmolar hyponatremia is caused by the addition of an ‘effective solute’ (e.g. glucose, mannitol or sucrose) to the serum. Commonly used as an osmotic laxative, PEG is described as ‘a nonabsorbable, nonmetabolized polymers’ that when administered orally acts as a ‘pure osmotic agent’ in the gastrointestinal tract. Systemic absorption can occur in rare cases. When PEG absorption occurs, most of its clearance occurs via renal filtration, this process is likely impaired in a patient with CKD such as seen in our patient.
When a patient presents with hyponatremia, the expectation of a low-serum osmolality needs to be confirmed with the actual measurement of serum osmolality. This case highlights the importance of detecting the etiology of hyponatremia without which treatment of the same can be impossible and expands the understanding of normal to high serum osmolality can go beyond the commonly known mannitol, paraproteinemia and lipidemia.