Variable distributions of serum creatine kinase reference values. Relationship to exercise activity.

Area of Science:

• Biochemistry
• Exercise Physiology
• Clinical Chemistry

Background:

• Serum creatine kinase (CK) activity is influenced by exercise.
• Current blood collection protocols lack standardization for CK analysis.
• Variability in CK reference ranges is often attributed to laboratory differences.

Purpose of the Study:

• To investigate the impact of exercise on serum CK activity and frequency distributions.
• To highlight the need for a standardized protocol for serum CK analysis.
• To evaluate the influence of exercise timing and type on CK levels.

Main Methods:

• Analysis of serum CK activity in different volunteer groups (students, nurses, mothers).
• Comparison of CK frequency distributions under varying exercise conditions.
• Monitoring CK levels over extended periods post-exercise.

Main Results:

• Serum CK activity showed variable frequency distributions (Gaussian to skewed) depending on exercise.
• Extremely high CK values were observed 5-8 days after eccentric exercise.
• CK levels in some individuals remained elevated for up to 15 days post-exercise.
• Peak CK values typically occurred within 24 hours of exercise.
• Standardizing exercise avoidance normalized skewed CK distributions in nurses.

Conclusions:

• A standardized protocol for serum CK analysis is essential due to exercise-induced variability.
• Documentation of physical activity, particularly eccentric exercise, for three weeks prior to sampling is recommended.
• Subject counseling to avoid unusual exercise and spaced sampling (3 tests, 1 week apart) are advised.