Pseudohyponatremia in pregnancy

A report describes a case of a 28-year-old woman with pregestational type I diabetes, well controlled with a mix of insulin aspart and insulin NPH, at 21 weeks gestation, who presented with a complaint of a throbbing headache for 12 hours. She gave a history of chronic migraines and sumatriptan consumption at symptom onset when not pregnant. However, she declined the usage of medication while pregnant as she was concerned about the effect of sumatriptan on her fetus. 

The physicians hospitalized her for the management of a headache. They found her blood pressure normal at 112/68, urine dip negative for protein, blood glucose level of 112 mg/ dL, and serum sodium as 111 mEq/L (further reconfirmed by repeat sodium level examination). They gave her restricted oral fluids and intravenous normal saline at 300 mL/h while awaiting the repeat sodium evaluation.

They found no improvement in serum sodium by repeat electrolyte panel and thus discussed the administration of hypertonic saline but did not implement it. The physicians calculated her osmolal gap and found it elevated at 58 mOsm/kg of H2O. They thought of possible ketoacidosis and performed an arterial blood gas evaluation, which revealed a normal pH (7.41). They thus made a diagnosis of pseudohyponatremia. 

The physicians' considered venous blood sample analysis on a blood gas machine, that uses a different methodology to assay serum sodium (direct potentiometry), and found the result as 138 mEq/L. They discontinued her Normal saline infusion and fluid restriction. Her serum cholesterol panel revealed total cholesterol of 1193 mg/dL, and lipoprotein electrophoresis revealed a triglyceride level of 3140 mg/dL and markedly increased chylomicrons. Her protein electrophoresis was normal.

Thus, clinicians must consider Pseudohyponatremia before initiating corrective measures for hyponatremia, especially in an asymptomatic patient. 

Source: Sosa M. Pseudohyponatremia in pregnancy. J Case Rep Images Obstet Gynecol 2022;8:100107Z08MS2022.