What is the equation for the CK Relative Index (CKI)?

The CK Relative Index (CKI) is an important calculation for assessing the proportion of creatine kinase (CK) isoenzymes in a patient's serum, particularly in the context of myocardial infarction. The correct equation for the CK Relative Index is derived from the relationship between the total CK activity and the activity of its isoenzyme, CK-MB, when considering the total CK (CKT).

The formula for the CKI is formulated as CKMB divided by the total CK activity (CKT), and then multiplied by 100 to express it as a percentage. This approach provides an accurate representation of the extent to which the MB isoenzyme contributes to the overall CK activity, which is crucial for diagnosing and managing cardiac events.

The rationale behind using this formula is that an elevated CK-MB level—specifically a significant increase in its relative proportion compared to the total CK—can indicate myocardial damage. By calculating the CKI in this manner, healthcare providers can more effectively assess the likelihood of heart-related issues.

This understanding is key for laboratory technologists interpreting test results and providing accurate information to facilitate clinical decision-making.