That test, whilst sensitive and accurate in detecting amatins is not FDA approved yet and not used for diagnostic purposes at this stage.
The FAQ put out by the manufacturer states as much and makes interesting and potentially relevant reading :
FAQ – AMATOXtest – a rapid, sensitive and simple test for amanitin
“
Is AMATOXtest a diagnostic test for amatoxin mushroom poisoning? The diagnosis of amatoxin poisoning in humans is based on a clinical triad that includes a history of foraged mushroom ingestion, vomiting and diarrhea beginning at least 6 and up to 24 hours later, and the subsequent development of liver injury as observed by climbing serum transaminase (liver enzyme) values. The diagnosis is more difficult in dogs as mushroom ingestion is often not observed and
dogs tend to be poor historians.
AMATOXtest may detect amatoxin in urine samples up to 3 days after an ingestion. Enough amatoxin is present in urine samples within 120 minutes after ingestion to be detected, and therefore a positive
AMATOXtest result is possible hours before any of the symptoms of amatoxin poisoning develop.
A positive result confirms the presence of amatoxin in a biological sample but
does not diagnose amatoxin poisoning.”
Edit : I see you found the same document.