title: Clinical evaluation of a new creatine kinase MB activity reagent abrogating the effect of mitochondrial creatine kinase.
abstract: BACKGROUND
  Measuring creatine kinase (CK) MB activity using the immunoinhibition method remains useful in clinical laboratories. CK-MB activity is abnormally high when macro CK type 2 (mitochondrial creatine kinase, MtCK) is present in patient serum. In order to improve the accuracy of the CK-MB activity assay, we developed a new CK-MB activity method using highly specific anti-MtCK antibodies. We evaluated the clinical performance of the new method, which abrogates the effect of MtCK activity.
  
  
  METHODS
  Receiver operating characteristic analysis, CK-MB activity range, cut-off, and CK-MB to CK activity ratio were investigated.
  
  
  RESULTS
  Mean CK-MB activity in normal human serum was 2.5 U/L by our method, in contrast to 12.0 U/L by the current method. Approximately 80% of CK-MB activity determined using the current kit corresponds to MtCK activity, and ubiquitous mitochondrial creatine kinase activity constitutes approximately 90% of MtCK activity. The cut-off and CK-MB activity ratio of our method were 12 U/L and 3 to 20%, respectively, in contrast to 22 U/L and 5 to 23%, respectively, using the current CK-MB method. The areas under the curve of our method, current CK-MB, electrophoresis, and CK-MB mass were 0.976, 0.928, 0.967, and 0.991, respectively. Our new method was superior to the electrophoresis and CK-MB mass as well as the conventional method due to jts promptness, simplification, and low cost.
  
  
  CONCLUSIONS
  The new kit will improve the clinical diagnosis of acute myocardial infarction. CK-MB activity assay was considered as a suitable alternative to conventional cardiac markers due to its superior diagnostic validity.
authors.affiliation: Division ofLaboratory Medicine, Department of Pathology and Microbiology, Nihon University School ofMedicine, Tokyo, Japan.
authors.forename: Tadashi
authors.initials: T
authors.lastname: Hoshino
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Sakai
authors.forename: Kazuaki
authors.initials: K
authors.lastname: Yamashita
authors.forename: Kouji
authors.initials: K
authors.lastname: Kishi
authors.forename: Katsuhisa
authors.initials: K
authors.lastname: Tanjoh
authors.forename: Atsushi
authors.initials: A
authors.lastname: Hirayama
authors.forename: Tomohiro
authors.initials: T
authors.lastname: Nakayama
mesh_terms: D052279:Creatine Kinase, MB Form / Q000097:blood*; D006801:Humans; D007202:Indicators and Reagents / Q000737:chemistry*; D008928:Mitochondria / Q000201:enzymology*; D012372:ROC Curve
chemical_list: D007202:Indicators and Reagents; D052279:Creatine Kinase, MB Form