Patient: I recently had my CPK checked approx 5 hrs after hiking for 2 hrs. I am in fairly good physical condition but have lupus. My CPK level came back 446. Could this elevation in CPK be attributed the exertion hiking and deerhunting the night before?
Doctor: Creatinine phosphokinase (CPK) is an enzyme found in skeletal muscle, cardiac muscle, and the brain. All of these areas have elevated serum levels of CPK when stressed; therefore, monitoring the serum level of CPK is important because elevated levels may indicate a serious health disorder, such as heart attack, stroke, or brain tumor. However, other factors such as age, sex, and exercise also affect CPK levels. In fact, elevated CPK is common in adults who exercise regularly. Normal levels of serum CPK vary from 0 to approximately 188 micrograms per liter. Different laboratories may report slightly different upper limits as within the normal range because of differences in test procedures and population differences. During exercise, especially of the high intensity burst type, considerable amounts of CPK leak into the extracellular fluid and plasma as a result of changes in membrane activity. The type of exercise and the duration affect the elevation of serum CPK. Non-weight-bearing activities such as rowing and swimming cause less pronounced CPK elevations than comparable weight bearing events. CPK elevations have been found to be linear with the duration of exercise up to 5.5 hours. Longer durations of exercise are associated with an accelerated increase in CPK. Exercise-induced increases in the level of serum CPK are temporary. Resting levels of CPK changes generally become elevated during exercise days and then return to normal levels during rest days. Peaks in serum CPK have been reported to occur at 5 minutes, 11 hours, 24 hours, 25 hours, and even 4-6 days following exercise. With continued physical activity, CPK levels remained elevated. Resting levels of serum CPK are higher in exercised trained individuals than in untrained ones. CPK elevations vary with age and sex. Older individuals are less likely to have elevations after exercise than are middle-aged or young adults. Women are more likely to have exercise induced elevations than are men.