Diagnosis, size estimation and prediction of acute myocardial infarction from S-myoglobin observations. A system analysis to assess the influence of various sources of variability.

Three different ways of using S-myoglobin observations for early diagnosis of acute myocardial infarction have been investigated by computer simulation techniques, viz. classification based on (i) single determination in relation to a decision limit, (ii) the peak serum concentration value, (iii) estimated or predicted value of infarct size from serial serum concentration determinations. The results of the in numero experiments indicate that it is possible to define optimal conditions with regard to time, period and frequency of observation, as well as to assess requirements on pre-analytical/analytical variation. The optimal time for a single observation should be about 10-12 h after onset of symptoms. The influence of pre-analytical/analytical variation is not very critical in this connection and the quality requirements are achievable in the clinical chemical laboratory today (total CV about 0.10). The peak serum value has good diagnostic power, but does not provide a good index of infarct size, no matter how good the analytical quality may be. It should be possible to predict infarct size from early serial S-myoglobin observations. A coefficient of pre-analytical/analytical variation below 0.05 is then required in addition to frequent blood specimen collection from admission up to peak time of the serum concentration curve.