"Extrapolated" creatine kinase-BB isoenzyme activity in assessment of initial brain damage after severe head injury.

The severity of initial brain damage is an important risk factor in determining the prognosis of head trauma. It can be assessed by assigning neurological scores or by determining the cerebrospinal fluid (CSF) activity of the isoenzyme creatine kinase-BB (CK-BB). In 10 severely head-injured patients serial CSF samples were obtained during the first 24 hours after trauma, and exponential decay of CK-BB activity with an average half-life of 4.5 hours was demonstrated. This finding led the authors to propose an "extrapolated" CK-BB activity, which theoretically occurs immediately after injury and is calculated from a single CK-BB recording, as a new index for assessing the degree of initial brain damage. In 50 patients with severe head injury, the prognostic ability of "observed" and "extrapolated" CK-BB activity was compared with two clinical scoring systems that evaluate severity of head trauma (the Glasgow and the Glasgow-Liege Coma Scales). "Extrapolated" CK-BB activity proved to be the best prognostic factor. With a CK-BB cutoff point of 330 U/liter, a true-positive rate of 79% and a true-negative rate of 73% were obtained. These results suggest the usefulness of measuring CK-BB activity in CSF as soon as possible after hospital admission for head injury.