The ACEP guidelines still have, as level B recommendations, that a single cardiac biomaker “8 to 12 hours” after symptom onset is adequate to exclude the diagnosis of NSTEMI.
This study looked at all of Highland’s patients that received more than one troponin measurement in their ED. Then, they looked at all the patients with initially negative troponins, and subsequently positive ones. And, finally, they tried to see how many of those had symptoms >8 hours. Their definitions are that troponins <0.06 ng/mL are negative, between 0.06 and 0.6 are indeterminate, and >0.6 are positive.
After starting with 5,596 patients, they had 125 that were negative initially, and then positive. And, for symptoms greater than 8 hours, a grand total of seven troponins ≤0.06 ng/mL and then subsequently positive, and 18 others that were indeterminate and then subsequently positive. They then say only two had a diagnosis of ACS.
Regardless, despite the size of the study, when you start talking about these sorts of tiny numbers and getting into splitting hairs on the diagnosis, you’re basically working on anecdotal evidence. So, take it with a grain of salt – you’re usually safe in a patient with that symptom duration, but you’re working off mostly consensus opinion as opposed to great evidence.
More interesting, really, would be some kind of follow-up on the 1,086 patients that were discharged after a single negative troponin (many of which probably fulfilled the >8 hour criterion) – but there’s no way to actually make that sort of follow happen realistically.