Radioimmunoassay of brain-type creatine kinase-BB isoenzyme in human tissues and in serum of patients with neurological disorders.

A sensitive radioimmunoassay for human brain type creatine kinase-BB isoenzyme has been used to measure the protein in serum as a potential index of central nervous system damage in patients with neurological disorders. The MB form of the enzyme (but not the MM form) partially cross-reacts in the radioimmunoassay but shows non-parallel dilution characteristics which distinguish it from the BB form of the enzyme. A survey of human tissues shows immunoreactive creatine kinase-BB in all human organs, with intestine and prostate approaching 35% of the brain concentration in contrast to the particularly low levels found in skeletal muscle, liver, spleen, and erythrocytes. No serum factors interfering in the assay were detected, and the normal serum level of creatine kinase-BB was found to be approximately 1-3 ng/ml. Serum containing high levels of immunoreactivity showed dilution characteristics paralleling the standard curve in the radioimmunoassay. Measurements of the protein in 47 patients with a variety of neurological disorders showed significantly raised mean levels in patients with dementia and with head injuries, isolated raised levels were also found in other disorders.