Prevalence of increased serum creatine kinase activity due to macro-creatine kinase and experience of screening programmes in district general hospitals

Background: Macro creatine kinase type 1 (MCK1) may be the cause of elevated total serum CK activity, which can lead to diagnostic confusion. There is evidence that this problem is poorly recognized perhaps due to a lack of information on its prevalence. Precipitation with polyethylene glycol (PEG) has been described for the detection of MCK1 but has not been fully evaluated.Methods: We introduced a screening programme to detect elevated serum total CK due to MCK1 and determine the prevalence of this problem using PEG precipitation with confirmation by gel filtration chromatography (GFC). The results were compared with those from a laboratory which selected samples for further investigation during the clinical validation process. We also studied characteristics of the PEG precipitation test including sensitivity and specificity when compared with GFC.Results: Over 2 years we screened 368 patients. In 17 cases the proportion of CK activity precipitated by PEG was relatively high and the presence of MCK1 wa...