title: The "normal" factor VIII concentration in plasma.
abstract: BACKGROUND
  The quantitation of factor (F)VIII by activity-based assays is influenced by the method, procedure, the quality and properties of reagents used and concentrations of other plasma proteins, including von Willebrand factor (VWF).
  
  
  OBJECTIVE
  To compare FVIII concentrations measured by activity-based assays with those obtained by an immunoassay and to establish the influence of plasma dilution on the FVIII clotting activity (FVIIIc).
  
  
  METHODS
  The APTT, a chromogenic assay (Coatest) and two in-house immunoassays were used. Albumin-free recombinant FVIII was used as the calibrator in all assays.
  
  
  RESULTS
  For a group of 44 healthy individuals (HI), the mean value observed for FVIII antigen (FVIIIag; 1.22+/-0.56 nM; S.D.) is substantially higher than that for FVIIIc (0.65+/-0.29 nM) and the chromogenic assay (FVIIIch; 0.50+/-0.23 nM). A positive correlation between FVIIIag and VWFag with R(2)=0.20 was observed. Since plasma VWF has an inhibitory effect on FVIIIc, we evaluated the influence of plasma dilutions on FVIIIc in HI (n=105). At a 4-fold dilution, estimates of FVIIIc by clotting assay were much lower than FVIIIag (0.77+/-0.31 vs. 1.14+/-0.48 nM). At 10- and 25-fold dilutions, the estimated FVIIIc increased to 0.87+/-0.36 and 0.94+/-0.44 nM, respectively.
  
  
  CONCLUSIONS
  1) In plasma, FVIIIag is higher than FVIIIc and FVIIIch; and 2) Real FVIII concentrations in plasma can be estimated by measuring FVIIIag.
authors.affiliation: Department of Biochemistry, College of Medicine, University of Vermont, Burlington, VT 05446, USA. sbutenas@uvm.edu
authors.forename: Saulius
authors.initials: S
authors.lastname: Butenas
authors.forename: Behnaz
authors.initials: B
authors.lastname: Parhami-Seren
authors.forename: Anetta
authors.initials: A
authors.lastname: Undas
authors.forename: David N
authors.initials: DN
authors.lastname: Fass
authors.forename: Kenneth G
authors.initials: KG
authors.lastname: Mann
mesh_terms: D000328:Adult; D004797:Enzyme-Linked Immunosorbent Assay / Q000379:methods; D005169:Factor VIII / Q000378:metabolism*; D005260:Female; D006467:Hemophilia A / Q000097:blood; D006801:Humans; D007118:Immunoassay / Q000379:methods; D008297:Male; D010314:Partial Thromboplastin Time / Q000379:methods; D010949:Plasma / Q000378:metabolism; D055815:Young Adult; D014841:von Willebrand Factor / Q000378:metabolism
chemical_list: D014841:von Willebrand Factor; D005169:Factor VIII
references.citation: Blood. 1984 Jun;63(6):1303-8
references.pmid: 6426549
references.citation: J Thromb Haemost. 2003 Aug;1(8):1771-6
references.pmid: 12911592
references.citation: Br J Haematol. 1982 Oct;52(2):259-67
references.pmid: 6812613
references.citation: Blood. 2009 Mar 12;113(11):2587-94
references.pmid: 19144987
references.citation: Arterioscler Thromb Vasc Biol. 2000 Aug;20(8):2024-8
references.pmid: 10938027
references.citation: Thromb Haemost. 2000 Jan;83(1):10-3
references.pmid: 10669146
references.citation: Br J Haematol. 1982 Aug;51(4):649-58
references.pmid: 6809034
references.citation: J Thromb Haemost. 2003 Sep;1(9):1927-34
references.pmid: 12941033
references.citation: Blood. 1981 Jul;58(1):1-13
references.pmid: 6165414
references.citation: Eur J Biochem. 1987 Jul 1;166(1):37-43
references.pmid: 3109914
references.citation: Thromb Res. 1975 Feb;6(2):109-18
references.pmid: 234637
references.citation: Thromb Res. 1991 Feb 15;61(4):385-93
references.pmid: 1905848
references.citation: Semin Thromb Hemost. 2002 Jun;28(3):247-56
references.pmid: 12098084
references.citation: Am J Clin Pathol. 2003 Jul;120(1):34-9
references.pmid: 12866370
references.citation: J Thromb Haemost. 2004 Apr;2(4):623-8
references.pmid: 15102018
references.citation: Thromb Haemost. 2001 Apr;85(4):580-3
references.pmid: 11341489
references.citation: Br J Haematol. 2007 Jan;136(1):138-45
references.pmid: 17222201
references.citation: J Biol Chem. 1988 Jul 25;263(21):10451-5
references.pmid: 3134349
references.citation: J Thromb Haemost. 2003 Nov;1(11):2283-9
references.pmid: 14629459
references.citation: Methods Enzymol. 1993;222:128-43
references.pmid: 8412790
references.citation: Br J Haematol. 2001 May;113(2):533-6
references.pmid: 11380427
references.citation: Blood. 1991 May 1;77(9):1929-36
references.pmid: 1902121
references.citation: Haemophilia. 2009 Jan;15(1):63-72
references.pmid: 18691375
references.citation: Thromb Haemost. 2003 Dec;90(6):1088-93
references.pmid: 14652641
references.citation: Thromb Haemost. 2000 Dec;84(6):942-8
references.pmid: 11154139
references.citation: J Thromb Haemost. 2009 Jan;7(1):132-7
references.pmid: 18983499
references.citation: J Biol Chem. 1989 Aug 25;264(24):14005-10
references.pmid: 2503509