31 - The impact of biochemical tests on patient management

Summary

Introduction

Biochemical testing is the ‘Gold standard’ for the diagnosis of acute myocardial infarction (AMI). Although the electrocardiogram (ECG) is the first test used for the differential diagnosis of patients who present with suspected acute coronary syndromes (ACS), the diagnostic accuracy of the ECG is only 55–75%. ST segment elevation has excellent specificity for AMI and identifies patients who will respond to thrombolytic therapy [1]. Biochemical tests form part of the World Health Organization criteria for AMI and have a diagnostic sensitivity of 95–100%.

The breakdown of diagnoses in patients with chest pain presenting to a typical district general hospital is shown in Figure 31.1. Only 10% have ST segment elevation AMI and the majority of patients have either low-risk ischaemic heart disease (IHD) or no IHD. Admission of these patient groups represents a significant waste of scarce healthcare resources. As only 10% of the patients present with characteristic ECG changes, biochemical diagnosis to confirm or exclude a diagnosis of AMI is required for 90% of the patients who present with suspected ACS. The role of the ECG is, therefore, to select patients for thrombolysis, not as the definitive diagnostic test for AMI. Creatinine kinase (CK)-MB is the best of the current enzymes and CK-MB mass the best test for the diagnosis of AMI according to current criteria [2]. Diagnosis can be achieved reliably within 12 hours from admission by serial measurement of myoglobin, CK or CK-MB.