title: Inter-method variability in bone alkaline phosphatase measurement: clinical impact on the management of dialysis patients.
abstract: BACKGROUND
  Bone-specific alkaline phosphatase (BAP) is now recommended to assess bone turnover in hemodialysis (HD) patients. However, little is known about potential variability between methods available to measure BAP.
  
  
  METHODS
  We measured BAP in 76 HD patients with six different assays (Beckman-Coulter Ostase IRMA, Beckman-Coulter Ostase Access, IDS iSYS Ostase, IDS Ostase enzyme immunoassay, DiaSorin Liaison Ostase and Quidel MicroVue BAP).
  
  
  RESULTS
  We observed a high correlation between all the assays ranging from 0.9948 (IDS iSYS vs. IDS EIA) to 0.9215 (DiaSorin Liaison vs. Quidel MicroVue). However, using the regression equations, the equivalent concentration of a Beckman-Coulter Access value of 10 μg/L can range from 7.7 to 14.4 μg/L and of 20 μg/L can range from 16.9 to 27.9 μg/L with other assays. According to Beckman-Coulter Access, 13%, 50% and 37% of the patients presented BAP values ≤10, between 10 and 20 and ≥20 μg/L, respectively. Discrepancies are observed when other assays are used (concordance from 10 to 100%).
  
  
  CONCLUSIONS
  Analytical problems leading to inter-method variation should be overcome to improve the usefulness of this marker in clinical practice. According to correlation results, recalibration of BAP assays is necessary but should not be a major issue.
authors.affiliation: Department of Clinical Chemistry, University of Liège, CHU Sart-Tilman, Liège, Belgium. Electronic address: Etienne.cavalier@chu.ulg.ac.be.
authors.forename: Etienne
authors.initials: E
authors.lastname: Cavalier
authors.affiliation: Laboratoire d'Explorations fonctionnelles, Hôpital Necker-Enfants maladies, Inserm U845, Paris, France.
authors.forename: Jean-Claude
authors.initials: JC
authors.lastname: Souberbielle
authors.affiliation: Department of Clinical Chemistry, University of Liège, CHU Sart-Tilman, Liège, Belgium.
authors.forename: Romy
authors.initials: R
authors.lastname: Gadisseur
authors.affiliation: Department of Nephrology, Dialysis and Hypertension, University of Liège, CHU Sart-Tilman, Liège, Belgium.
authors.forename: Bernard
authors.initials: B
authors.lastname: Dubois
authors.affiliation: Department of Nephrology, Dialysis and Hypertension, University of Liège, CHU Sart-Tilman, Liège, Belgium.
authors.forename: Jean-Marie
authors.initials: JM
authors.lastname: Krzesinski
authors.affiliation: Department of Nephrology, Dialysis and Hypertension, University of Liège, CHU Sart-Tilman, Liège, Belgium.
authors.forename: Pierre
authors.initials: P
authors.lastname: Delanaye
mesh_terms: D000368:Aged; D000469:Alkaline Phosphatase / Q000378:metabolism*; D015415:Biomarkers / Q000378:metabolism; D001842:Bone and Bones / Q000378:metabolism*; D005260:Female; D006801:Humans; D007124:Immunoenzyme Techniques / Q000379:methods; D007674:Kidney Diseases / Q000378:metabolism*; D008297:Male; D006435:Renal Dialysis / Q000379:methods
chemical_list: D015415:Biomarkers; D000469:Alkaline Phosphatase
keywords: Analytical variation; Bone-specific alkaline phosphatase; Dialysis patients; Standardization