Myocardial infarction: serum creatine kinase diagnosed it

Clinical bottom line (level 4)

  1. Two thirds of patients with a suspected MI had one.
  2. Patients with suspected MI who had a serum creatine kinase level of 280 IU/L or more were very likely to have had an MI (LR+54.3) .
  3. Patients with a serum creatine kinase level of 80 to 279 IU/L were likely to have had an MI (LR+4.45) .
  4. Patients with a creatine kinase level of 40 to 79 IU/L were less likely to have had an MI (LR-0.30) .
  5. Patients with a creatine kinase level of less than 40 IU/L were much less likely to have had an MI (LR-0.01) .
Smith : Lancet 1967; : 178-182
Expires March 2003

The study

Setting: coronary care unit, UK

400 patients (aged ?, ?% male) suspected myocardial infarction

Independent ?blinded reference standard, applied in all patients from a consecutive inappropriate spectrum.
Reference standard:
  • Patients were classified into four groups according to World Health Organisation (1959} categories: 1. very probable MI- ECG with pathological Q waves, ST-segment elevation, and T-wave inversion; 2. possible MI- less diagnostic ECG abnormalities- ST-segment and T wave changes only; 3. coronary insufficiency- history typical of cardiac pain unaccompanied by anything more than transient ECG abnormalities; 4. miscellaneous. To determine normal creatine kinase levels 111 patients with no serious illness had their levels measured. 40 IU per litre was taken as the upper limit of normal.
Diagnostic test: Serum creatine kinase level- obtained at admission and on following two mornings. Measured in most cases, on day of receipt of specimen.
  • Possible myocardial infarction was considered along with very probable myocardial infarction when analysing the diagnostic test.

The evidence


diagnostic test MI or possible MI no MI LR
(95% CI)		 post-test probability
creatine kinase =280 IU/L 96 1 54.3
(7.66 to 384) 		99.0%
creatine kinase 80-279 IU/L 118 15 4.45
(2.72 to 7.27) 		89.0%
creatine kinase 40-79 IU/L 14 26 0.30
(0.16 to 0.56) 		35.0%
creatine kinase <40 2 88 0.01
(0.00 to 0.05) 		2.00%
total 230 130

Comments

  1. Technique for measuring CK no longer widely used, and reference standard used now superceded (partly as a result of this study).
  2. Unstable angina (group 3) s now diagnosed and managed very differently

Citation

  1. Smith AF, : Diagnostic value of serum-creatine-kinase in a coronary-care unit. Lancet 1967; : 178-182
Contributor: Clare Wotton and Musab Hayatli, January 2000
Reviewer: Donald E. Stanley

Clinical Question.
Patient myocardial infarction
Intervention or Exposure serum creatine kinase levels
Comparison normal
Outcome diagnosis