Antech Diagnostics will no longer offer an Ammonia Level as a test of hepatic function. The necessity of careful sample preparation, combined with transportation time, limits the usefulness of this test in most clinical settings. Accurate results depend upon the use of ammonia-free heparin as the anticoagulant, continuous icing of the sample once drawn, immediate plasma separation (red cells contain ammonia and can create a false elevation), and immediate assay (within one hour of collection), as the ammonia is volatile. Clearly, these restrictions make it a cumbersome test of questionable diagnostic usefulness.

The Bile Acids Assay provides similar diagnostic information and is the test of choice, when evaluation of hepatic function flow and function is required.