Capillary and venous samples of total creatine kinase are similar after eccentric exercise

Circulating creatine kinase (CK) levels are often monitored as an indirect biomarker of muscle damage after resistive exercise. The purpose of the present investigation was to evaluate whether capillary whole-blood sampling, a simpler and less invasive method for obtaining a venous blood sample, would allow for a reliable measurement of total CK compared to venipuncture. Fifteen untrained subjects performed 50 maximal eccentric elbow extensions to induce muscle damage of the biceps brachii. Capillary (fingerstick) and venous whole-blood samples were collected contemporaneously at baseline and again at 24, 48, 72, and 96 hours post-exercise. Using a commercial CK analysis kit with a protocol modification to account for a reduced sample size, total CK activity of the capillary and venous samples was analyzed concurrently via spectrophotometry. Results indicated a 0.997 correlation between sampling sites for total CK, with disagreement between the venous and capillary samples estimated at <12% across the range of CK values. These findings indicate capillary sampling for total CK activity provides a valid alternative to venipuncture and should be considered by researchers, clinicians, and strength and conditioning specialists as an alternate sampling technique when indirectly evaluating muscle damage after exercise.