Significance of elevated MB isoenzyme with normal creatine kinase in acute myocardial infarction
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Elevated creatine kinase-MB (CK-MB) with normal creatine kinase (CK) levels may indicate missed myocardial infarction diagnoses due to standard "normal" ranges. Careful enzyme analysis is crucial for accurate AMI detection.
Area of Science:
- Cardiology
- Biochemistry
- Clinical Diagnostics
Background:
- Acute myocardial infarction (AMI) diagnosis relies on cardiac enzyme levels.
- Elevated creatine kinase-MB (CK-MB) is a key indicator, but its interpretation alongside total creatine kinase (CK) levels requires careful consideration.
Purpose of the Study:
- To investigate the significance of elevated CK-MB levels when total CK levels are within the normal range in patients with suspected AMI.
- To evaluate the impact of standard diagnostic criteria on the detection of myocardial injury.
Main Methods:
- Analysis of CK and CK-MB levels in 400 patients with suspected AMI.
- Categorization of patients into groups based on enzyme elevation patterns.
- Assessment of enzyme curves and baseline levels to identify potential missed elevations.
Main Results:
- In 57% of patients with only CK-MB elevated, total CK levels doubled within the normal range, suggesting missed elevations.
- Patients with elevated CK-MB and normal CK had a significantly greater median CK increase compared to those with no enzyme elevation.
- Standard diagnostic approaches could miss significant CK elevations in a substantial number of AMI cases, particularly with limited sampling.
Conclusions:
- Arbitrary definitions of
- normal
- CK levels may lead to underdiagnosis of myocardial infarction.
- A significant proportion of patients with suspected AMI may be misclassified due to reliance on standard enzyme thresholds.
- More sensitive diagnostic criteria or increased sampling frequency may be necessary for accurate AMI detection.
Abstract:
The significance of elevated levels of the MB isomer of creatine kinase (CK-MB) when creatine kinase (CK) level is normal was studied in 400 patients with suspected acute myocardial infarction (AMI). In 350 patients both CK and CK-MB were elevated (group 1), in 21 only CK-MB was elevated (group 2), in 24 neither enzyme was elevated (group 3) and in 5 only CK was elevated (group 4). In 57% of patients in group 2 the CK level was doubled, with a characteristic enzyme curve, within the normal range, suggesting that an increase in CK had been missed because arbitrary definitions of "normal" were used. The median CK increase (60 IU/liter) in group 2 was greater than that in group 3 (23 IU/liter) (p less than 0.001). Patients in group 1 with small AMIs had a relative increase in CK similar to that in group 2. However, patients in group 2 had a lower baseline CK level so that peak CK did not become abnormally high despite a 5-fold increase in some patients. In patients in group 1 with small AMIs, CK was elevated in fewer samples than CK-MB. If only 2 samples were obtained in all patients, elevation of CK levels would have been missed in 63 group 1 patients, erroneously increasing the number of patients in group 2 fourfold (to 84 of 400, or 21%, instead of 21 of 400, or only 5%). Conversely, if patients in group 2 with a doubling of CK are excluded, the prevalence of elevated CK-MB with normal CK would be only 9 of 400 (2%).(ABSTRACT TRUNCATED AT 250 WORDS)