The proportion of hyponatremia in the elderly group was higher than that in the nonelderly group, which is consistent with previous studies.[22,23] The hyponatremia may be due to the syndrome of inappropriate secretion of antidiuretic hormone, renal salt-wasting syndrome as part of dysautonomia, use of immunoglobulin, etc.[23] However, we could not confirm the certain cause of hyponatremia in the study because we had not examined the antidiuretic hormone, the urine volume, and blood volume of the patients. This evidence concerns the gene AVP and dysautonomia.