Early diagnosis of acute myocardial infarction.

REPLY,-My article made clear that single enzyme measurements are rarely diagnostic in the first 12 hours.Serial measurements are more useful, but in the real world of a busy hospital and an understaffed biochemistry laboratory this is unlikely to find much favour, particularly when the method requires four hourly blood sampling and construction of a "log creatine kinase slope."Even if the method were practicable it would not permit diagnosis until 12 hours or more after admission (perhaps 16 hours after infarction), when the benefits of thrombolytic treatment are considerably diminished and when electrocardiography often shows unequivocal changes.Practical considerations aside, I am less enthusiastic than Dr Mullen about the validity of this method.The main differential diagnosis in patients with cardiac chest pain is between unstable angina and acute infarction.Difficulties arise only if the electrocardiogram taken on ad- mission to hospital is non-diagnostic, and an additional test may be required.Collinson et al gave no information about admission electro- cardiograms, and in the 1989 study only one patient had unstable angina compared with 34 with acute infarction-which makes it difficult to assess the test's discriminatory value.Indeed, they seem to acknowledge this difficulty by diagnosing five patients as "ischaemia ?infarction," a conundrum