Which statement correctly matches isotonic hyponatremia with its associated condition?

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Isotonic hyponatremia, also called pseudohyponatremia, happens when the serum osmolality is normal but the measured sodium appears low due to a lab artifact from high levels of nonaqueous substances in the blood. The classic culprits are severe hyperlipidemia or hyperproteinemia. In these states, the plasma water fraction is reduced, and indirect ion-selective electrode methods assume a normal water fraction, leading to a falsely low sodium reading even though the true sodium concentration in the water phase is normal. Since the osmolality is unchanged, this is considered isotonic hyponatremia.

Hyperlipidemia fits this pattern because the excess lipids trap the measurement in a way that makes sodium look low without changing the serum’s osmolality. Hyperglycemia, in contrast, raises serum osmolality and causes hypertonic hyponatremia rather than isotonic. Electrolyte abnormalities like hyperkalemia or hypophosphatemia do not produce this pseudohyponatremia artifact.