• BIOCHEMISTRY
• LABORATORY TESTS
• QUANTITATION

To the Editor,

We read with interest the letter by Schuff-Werner and Steiner1 that commented a recently published article dealing with the evaluation of the short- and long-term storage stability of plasma ammonia.2 We were particularly impressed by the authors’ claim that blood ammonia values may significantly depend on the activity of γ-glutamyl-transferase (GGT) in plasma. They support this conclusion by reporting experimental results obtained in two samples with low and increased GGT catalytic concentrations stored up to 6 h either at room temperature or at 4°C.1

Several, mostly preanalytical, factors, like haemolysis and poor specimen quality, skin contamination and delayed analysis in general, may cause artificial increase of blood ammonia.3 ,4 If the systematic detection of haemolysis through the automatic photometric measurement of haemolysis index (HI) is now relatively common, it is more difficult for laboratories to keep the time short between blood drawing and analysis. To prevent an artificial increase of ammoniaemia caused by the metabolism of red blood cells due …