Hyponatremia due to excess natriuresis

Nine cases with hyponatremia were precisely examined during the past 2 years. Seven of them showed normal plasma volume, serum aldosterone and pituitary function, although ADH was detected. Therefore, those seven cases were diagnosed without dilutional hyponatremia due to SIADH (a syndrome of inappropriate secretion of antidiuretic hormone). The mechanism of hyponatremia of such a type has not been yet explained definitely, but it may be referring to excess natriuresis. Only each one case of hyponatremia due to hypopituitarism and dilutional hyponatremia due to SIADH was verified in this series. SIADH showing high plasma volume value was thought to be rare. Differential diagnosis between SIADH and hyponatremia due to excess natriuresis is essential and simple. Non-invasive plasma volume measurement using RISA is significantly useful for it. For the hyponatremia due to excess natriuresis, water restriction is not necessary, but digestive supply of NaCl is needed.