Measurement of ammonia is problematic as it rapidly increases with storage in whole blood and also increases with storage in separated plasma. As a result the following handling collection and handling instructions should be followed:

Mailed-in samples or samples that will not reach the lab within an hour of sampling:

Blood should be collected into EDTA or heparin tubes, separated immediately and the plasma should be frozen.  The frozen plasma sample should be shipped to the lab on dry ice (needs to stay frozen).  Mark the outside of the shipping box in large letters with the following: PERISHABLE KEEP FROZEN.  If the sample arrives at the lab thawed a comment will be added indicating that the ammonia value may be falsely increased from storage.

Local clients within a 1 hour drive from the lab:

Blood should be collected into EDTA or heparin tubes, separated immediately and the plasma kept on ice until analysis. Ammonia is stable in plasma for a maximum of 3 hours under these conditions. If sample separation from cells cannot be achieved, the sample should be kept on ice until submission to the laboratory, however ammonia will be less accurate. Mark the outside of the shipping box in large letters with the following: PERISHABLE KEEP COOL.