What is the normal range of creatine kinase (CK) for well-muscled men who lift weights?—CHARLES LIANG, DO, Bloomington, Ill.

To my knowledge, there is no well-accepted reference range for CK in this population. However, it is generally accepted that serum levels of CK are affected by lean body mass, gender, race, and muscle activity. The reference range for males (55-170 units/L) is higher than for females (30-135). Persons of African descent typically have values 30% higher than other persons. Regular exercise, particularly strength training, increases serum CK by about 50% (Clin Chem. 1998;44:A136). Putting all this together, it’s entirely possible that well-muscled men who lift weights may have CK values that exceed the usual reference range for men.—Walter N. Kernan, MD (148-6)