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I agree with Paul Collinson (message 1/9/02) that timing depends upon prior probability and acceptable miss rate, but disagree with the way he has calculated miss rate. Missing 45 out of 50 MIs is a miss rate of 10% in my book, not 0.5% as was calculated based on a population tested of 1000. I am also concerned with the testing policy (of Jonathan Kay) that states that a second specimen at 12 hour post onset of symtoms should always be collected for TnI in addition to a first specimen obtained when patient is first seen. The concern I have with this strategy is that many of the patients tested (>50% in our locale) at 1 or 2 hours after presentation do not get another blood sample collected for TnI for a number of reasons, one being that the patient has been sent home. It does not seem practical to me to force the Emergency Dept to test again at 12h in all patients initially tested because a TnI was ordered on presentation, as much as we may think this is the right thing to do. This takes me back to the point made by Paul Collinson that a testing strategy should take into account timing practicality and acceptable miss rate. If a 10% miss rate is acceptable (as was suggested it is) and this is acheived at 6h post onset of symptoms, then I would suggest that the first specimen be collected at this time and not before. This way no patient would be sent home with a TnI test performed on blood collected 1 hour after presentation as is the case now. I can think of one other testing strategy alternative when troponin is the only biochemical marker available. Collect first specimen on presentation and again after 6-8 hours, but analyze TnI on both only when the second specimen is taken. I would appreciate any feedback on this.