The value of urinary chloride measurement in distinguishing surreptitious vomiting from Bartter's syndrome.

Urinary chloride measurement is a simple and common procedure but its value in clinical practice is not extensive. This case report highlights a practical and important use of this test. A patient presented with most of the clinical and metabolic derangements of Bartter's syndrome but was found to have extremely low or absent urinary chloride excretion. Her ability to excrete chloride was, however, intact during a chloride load test. The finding of low urinary chloride excretion did not support the diagnosis of Bartter's syndrome and suggested an extrarenal loss of chloride. This was confirmed when she eventually admitted to surreptitious vomiting.