PETER U. FEIG, M.D.; RICHARD H. STERNS, M.D.
To the editor: In a recent report of another case of carbamazepine-induced hypotonicity (1), the authors claim that "inappropriate antidiuresis can be diagnosed when hyponatremia with serum hypo-osmolal to urine occurs . . ." This may well be the most widespread misconception in the diagnostic evaluation of hypotonic states. The appropriate response to hypotonicity is diuresis via maximal urinary dilution, that is, urinary osmolality (Uosm) in two-digit range. Any Uosm greater than 100 mosmol/kg H2O represents some degree of antidiuresis (2). Hyponatremia develops when water intake exceeds total water losses and it is maintained by zero water balance (in spite
FEIG PU, STERNS RH. Diagnosis of Hypotonic States. Ann Intern Med. ;88:717. doi: 10.7326/0003-4819-88-5-717_1
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Published: Ann Intern Med. 1978;88(5):717.
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