Spurious brain creatine kinase in serum from patients with renal disease.

Creatine kinase isoenzyme I(BB) is generally not detectable in normal serum, and its occurrence in serum has been documented in only a few disease states. In particular, increased activity of this isoenzyme has been reported in association with chronic renal failure, hemodialysis, and renal transplantation. The present study demonstrates that the apparent creatine kinase observed in the serum of such renal patients is an artifact, observed as a result of measuring creatine kinase isoenzymes by fluorescence. Our observations resemble those of McKenzie et al. [Clin. Chim. Acta 70, 333(1976)] concerning an artifact in the fluorometric determination of lactate dehydrogenase isoenzymes in the sera of patients with end-stage renal failure. The artifact binds to albumin, is not a protein, and occurs in some normal sera at very low concentrations. This artifact can be mistakenly identified as isoenzyme I in renal-disease patients if CK isoenzymes are determined fluorometrically.