Table 2 Deviations from the 0/1/4-hour OUT-ACS protocol (n = 86)

Rule-out group

(n = 25)

4-hour hs-cTnT collected without indication (n = 25)

• Subject to unnecessary repeated testing after being ruled out by the 0/1-hour samples.

• Resulted in prolonged observation and delayed time before conclusive decision.

Observation group

(n = 57)

1-hour hs-cTnT missing (n = 32)

• 0-hour < 12 ng/L (n = 25)

 o Potentially rule-out cases if a 1-hour sample had been collected.

• 0-hour 12–14 ng/L (n = 1)

• 0-hour  above the 99th percentile URL; >14 ng/L (n = 6)

 o Median hs-cTnT 18 ng/L (IQR 15–23)

 o Patients with myocardial injury. Without the 1-hour measurement, it was not possible to distinguish acute from chronic injury (i.e., a potential safety issue).

4-hour hs-cTnT missing (n = 26)

• Median hs-cTnT 12 ng/L (IQR 11–16)

• Most had stable 0/1-hour measurements above the rule-out threshold of 11 ng/L (e.g., 0/1-hour hs-cTnT pairs of 12–12 ng/L, 17–17 ng/L, or 16–16 ng/L).

Rule-in group

(n = 4)

4-hour hs-cTnT missing (n = 4)

• Discharged home after being discussed with the on-call hospital specialist.

• The elevated hs-cTnT levels were interpreted as habitual or non-ischaemic before being advised against further testing.