Timed sequential analysis of creatine kinase in the diagnosis of myocardial infarction in patients over 65 years of age.

Abstract

Aim-To assess the value of timed sequential analysis of creatine kinase (CK) activity for the early diagnosis of acute myocardial infarction (AMI) in patients over 65 years of age. Method-Samples were collected on admission and eight to 12 hours later from 156 patients over 65 years of age. Routine cardiac enzyme activities were determined and serial electrocardiograms (ECGs) Measurement of timed sequential creatine kinase (CK) activity in serum has been proposed as one method for early confirmation of a diagnosis of AMI.'-Like other tests for the diagnosis of AMI, this test has been evaluated in patients admitted to a coronary care unit,' 2 however, only small numbers of patients were included in these early studies. Other investigators who studied slightly larger groups of patients found that the test gave false negative results and could not be used to exclude reliably a diagnosis of AMI.78 Although a coronary care unit provides a well controlled environment in which to conduct the evaluation of a test requiring carefully timed samples, the populations studied so far have been preselected with a high incidence of AMI, up to 55%,9 and other possible confounding diagnoses may have been excluded. As a result, the test's performance may not be as accurate when evaluated in unselected elderly subjects presenting with acute chest pain. This group of subjects may also have other potential confounding diagnoses not found in younger age groups.The predictive value of a test improves with selection of the population studied and collection of samples under well controlled conditions. We therefore investigated the value of this test in patients over 65 years of age admitted to a busy district general hospital with acute chest pain.Over five months, 156 patients (88 women) presenting with acute chest pain were studied. All were over 65 years of age. The time of onset of chest pain in relation to the time of admission was recorded. Three serial electrocardiograms (ECGs) were collected, standard cardiac enzyme activities comprising total CK and lactate dehydrogenase (LDH) were determined on the three days following admission, and the results recorded. The final diagnosis at the time of discharge was also recorded.The study was approved by the District Ethics Committee and all patients gave informed consent. MethodsBlood samples for timed CK analysis were collected on admission and eight to 12 hours later. All blood samples for cardiac enzyme analysis were centrifuged, the serum separated and analysed at the time received to simulate the provision of a routine clinical service.Creatine kinase activity was measured at 37°C with a Beckman CX7 analyser (Beckman Instruments, High Wycombe, UK) using commercially available reagents (Randox, Dublin, Republic of Ireland). The between batch imprecision of this method was 4-1% at 147 IU/l and 2-3% at 467 IU/1. The laboratory upper reference range for CK was 195 IU/l for men and 170 IU/l for women.Lactate dehydrogenase activity was measured using the same instrument and reage...

Creatine kinase isoform electrophoresis for the early confirmation of myocardial infarction detected by timed sequential CK slope analysis

“…The validity of this cut-off had previously been confirmed in a study of elderly individuals. 4 Throughout their stay in hospital, patients' treatment and further investigation continued under the direction of the consultant who was responsible for their care. The results of timed CK analysis and CK isoform analysis were not made available to the consultant responsible for the patient's care.…”