Preservation of urine with sulfamic acid in soluble packages.

Urine samples must be acidified if accurate calcium analyses are to be obtained (1). In many institutions the nursing staff is not permitted to dispense the strong acids traditionally used to decrease the pH of urine, so that the acid must be transferred into the collection vessels in the clinical laboratory. To avoid the dangerous practice of using a caustic liquid acid as a preservative, we have enclosed a dry strong acid in a water-soluble plastic envelope, which can be included with the urine container. In this way a predetermined quantity of acid may be dispensed safely.