Ruling out AMI with 99.7% certainty from the first blood sample
Blood samples
In the US and Europe, approximately 15 million patients present each year to emergency departments (ED) with chest pains or other symptoms of acute myocardial infarction (AMI). However the vast majority of such patients presenting to the ED turn out not to have AMI. Currently electrocardiography (ECG) and the measurement of cardiac troponin levels form the diagnostic basis to complement clinical assessment of these patients. However nearly a third of all patients with AMI present without any significant ECG changes so in practice ECG is actually of little help in “ruling out” AMI. As for assays for Troponin, they have the limitation that there is a sensitivity “deficit” in the initial period after AMI. This means that a prolonged period of close patient monitoring is required, including the taking of serial blood samples.
Recent work (Reichlin T et al. Incremental value of copeptin for rapid rule out of MI. J Amer Coll Card 2009; 54: 60) has shown that the combination of measurements of circulating troponin and of copeptin can dramatically improve the possibility of ruling out AMI. Copeptin is a 39 amino acid glycopepetide that makes up the C-terminal part of the arginine vasopressin (AVP) precursor. The AVP system has long been known to play a crucial role in the regulation of endogenous stress response but diagnostic use of this property has been limited because of the short half-life of AVP. Copeptin however is much more stable. An automated immunofluoroscent assay has now been developed to determine circulating copeptin levels. Copeptin is a marker of endogeneous stress, and plasma levels increase immediately after the onset of AMI. The recent work investigated the combination of copeptin and Troponin measurements in 487 patients to rule out AMI. Patients negative for both markers could be ruled out for AMI at initial presentation with a negative predictive value of 99.7% and without the need for serial blood sampling. Thus, 65% of all the patients presenting to the ED were ruled out for AMI at the first blood sample.
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