Evaluation of the enzymatic ammonia method for urine on the Du Pont automatic clinical analyzer

The enzymatic method for ammonia with the Du Pont Automatic Clinical Analyzer was tested in our laboratory. The method is very suitable for urine samples although the method was released by Du Pont only for plasma samples. The results correlated well with those obtained by a method based on the Berthelot indophenol reaction and by a method based on the use of an ammonium electrode, which has an ammonium ion selective membrane. The day-to-day coefficient of variation is about 2 and 4% at concentration levels of 100 and 50 mumol/1 respectively. The measured and relative ammonia concentration are linearly related. Recovery of added known amounts of ammonium is complete and no interference from glucose, urea, creatinine and uric acid could be demonstrated. Recommendations are given for handling blood and urine samples before analysis.