Spurious Hyponatremia: Back to the Laboratory
Chitturi C, and Soman S. SPURIOUS HYPONATREMIA: BACK TO THE LABORATORY. Am J Kidney Dis 2019; 73(5):663.
Am J Kidney Dis
Hyponatremia (hypoNa) occurs in 15%–30% of hospitalized patients. Spurious hypoNa requires etiologic diagnosis but not therapy. This report describes pseudohyponatremia (PHNa) attributed to a systematic laboratory defect. Four patients with AKI were identified with 6-10mmol/L drop in serum sodium (SNa) overnight. This drop couldn't be explained physiologically on review of last 24hrs intake/output. They were asymptomatic. Hence serum osmolality (Sosm) and whole blood Na were performed. Fig1 indicates PHNa with concern for lab error. Two of the four patients were dialysis dependent. We avoided adjusting dialysate Na, which could have induced true hypoNa due to confirmatory testing. General causes of PHNa are hypertriglyceridemia & paraproteinemia. In our cases, it turned out to be lab error due to a dysfunctional electrode in the indirect Ion specific electrode (ISE) analyzer. Indirect ISE is commonly employed in most hospitals to test SNa. It uses a small serum volume by a preanalytic dilution step. It is important to confirm hypoNa with Sosm and direct ISE which measures the Na concentration in the water phase of serum. If direct ISE is unavailable the SNa can be estimated. Fig2 SNa is one of the most frequently requested blood tests. It is imperative we understand how to interpret and investigate if there is a concern for PHNa. The dangers of failing to recognize and treating as if it were true hypoNa could potentially lead to dangerous consequences. [Figure Presented][Figure Presented]