When the Numbers Lie: Uncovering Pseudohyponatremia After an Anabolic Steroid Injection.

Pseudohyponatremia is a laboratory artifact in which serum sodium levels appear falsely low despite normal serum osmolality. It typically occurs in the presence of hypertriglyceridemia or paraproteinemia, but this case highlights a rare etiology: inadvertent intravenous injection of an oil-diluted anabolic steroid. A 42-year-old healthy man presented to the emergency department with nausea, vomiting, and presyncope. He reported injecting trenbolone intramuscularly three days prior and noted blood aspiration before injection, suggesting possible intravenous administration. He denied other recent illnesses or exposures. On examination, he was afebrile, hemodynamically stable, and non-toxic, with an unremarkable physical exam. Initial laboratory results revealed a serum sodium level of 125 mmol/L. However, the measured serum osmolality was 289 mOsm/kg while the calculated osmolality was 259 mOsm/kg, revealing an osmolal gap. A point-of-care iSTAT revealed a sodium level of 137 mmol/L, indicating true normonatremia and supporting the diagnosis of pseudohyponatremia. Additional labs showed erythrocytosis, consistent with anabolic steroid use, and no evidence of hypertriglyceridemia or paraproteinemia. Nephrology was consulted due to concern for symptomatic hyponatremia. With a normal measured osmolality, normal lipid and protein levels, and a history of recent anabolic steroid injection, the low serum sodium level was attributed to a laboratory artifact resulting from nonaqueous solvent interference. The patient was admitted for observation and remained stable, with improving symptoms and normalizing labs. Serum sodium by main-lab indirect analysis was 136 mmol/L by the time of discharge on hospital day two. He was discharged with outpatient follow-up. In patients with unexplained hyponatremia and normal clinical status, pseudohyponatremia must be considered. Prompt recognition can prevent unnecessary treatments, reduce patient risk, and guide appropriate care.