Measurement of the blood ammonia level

A venous blood sample was collected from each patient after at least 6 hours of fasting, and 9 hours avoidance of smoking, making sure that the patients had followed the instructions not to perform any physical exercise the day before. The samples were put into sterile specimen tubes containing EDTA as an anticoagulant.

The samples were transported on ice to the laboratory, separated within 15 minutes of collection, and analyzed immediately. These precautions are necessary as the ammonia content of standing blood increases spontaneously, due to generation and release of ammonia from red blood cells and, to a lesser extent, the deamination of amino acids by enzymes in the circulation.