Detection of creatine kinase macroenzymes.

Background: It is vital to detect macroenzymes in patients' plasma or serum since their presence may lead to spurious elevation of enzyme activity, thereby causing diagnostic confusion. Our service for macroenzyme detection has been made available to laboratories throughout the UK. This report describes our laboratory's experience with macro-creatine kinase (CK) detection over a 10-year period.

Methods: In each sample received, the presence of macro-CK was looked for by both polyethylene glycol percent precipitable activity (%PPA) and isoenzyme electrophoresis (IsoEP). The accumulated findings over 10 years were reviewed.

Results: Out of a total number of 255 requests received from throughout the UK, 30 patients (11.8%) were found to be positive for macro-CK (28 type 1 and 2 type 2). Among those found to be positive, the total CK elevation was relatively modest and the %PPA positively correlated with macro-CK by IsoEP and densitometry (Spearman r(s) = 0.631). The upper reference limit for %PPA of CK could be increased from 37% to 45% after assessment by both an International Federation of Clinical Chemistry-approved calculation and by receiver operating characteristic curve analysis.

Conclusions: Adoption of this change would allow for a more cost-effective investigation protocol. More than 80% of those positive for macro-CK type 1 (immunoglobulin bound) were female, which conforms to findings in many autoimmune processes.