title: Prevalence of increased serum creatine kinase activity due to macro-creatine kinase and experience of screening programmes in district general hospitals.
abstract: 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 was confirmed in seven by GFC. In a second laboratory, over a period of 5 years, 11 samples were selected during the clinical validation process for further study and MCK1 was the cause of the elevated CK activity in six cases. PEG precipitates a proportion of normal, uncomplexed CK and this is increased by increasing serum globulin concentration and by higher concentrations of PEG.
  
  
  CONCLUSIONS
  The prevalence of elevated serum CK activity due to MCK1 was approximately 2%. Laboratories should consider introducing a systematic screening programme based on PEG precipitation.
authors.affiliation: Department of Clinical Biochemistry, Southend Hospital, Westcliff-on-Sea, Essex, UK. mfahie-wilson@southend.nhs.uk
authors.forename: Michael N
authors.initials: MN
authors.lastname: Fahie-Wilson
authors.forename: Sally
authors.initials: S
authors.lastname: Burrows
authors.forename: Graham J
authors.initials: GJ
authors.lastname: Lawson
authors.forename: Tania
authors.initials: T
authors.lastname: Gordon
authors.forename: Way
authors.initials: W
authors.lastname: Wong
authors.forename: Bhaskar
authors.initials: B
authors.lastname: Dasgupta
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D011232:Chemical Precipitation; D002850:Chromatography, Gel; D003093:Colitis, Ulcerative / Q000201:enzymology*; D003402:Creatine Kinase / Q000097:blood*; D005189:False Positive Reactions; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011092:Polyethylene Glycols / Q000494:pharmacology; D015995:Prevalence; D012016:Reference Values; D012680:Sensitivity and Specificity; D013997:Time Factors
chemical_list: D011092:Polyethylene Glycols; D003402:Creatine Kinase