The “normal” factor VIII concentration in plasma

Abstract

Introduction 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 R2=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.

Determining Concentrations of Factors VIII, IX and Fibrinogen in Fresh Frozen Plasma: An Alternative to Improve Treatment of Hemorrhagic Diseases in a Developing Country

“…In this study, mean concentrations were respectively 0.4±0.4 IU/mL for factor VIII, and 0.3±0.2 IU/mL for factor IX. Our values are lower than mean concentrations of factors VIII and IX, reported in the literature [12,17,18], which varies between 0.7 and 1 IU/mL for factor VIII. This difference could be due to the methods of plasma preparation.…”

CD4 T cells specific for factor VIII are present at high frequency in healthy donors and comprise naïve and memory cells

“…17 It was however below the frequency found for strong immunogens, such as KLH, 15,18 and it was too low to be detected without any in vitro culture phase. The data suggest that the basal level of expression of endogenous FVIII (ie, 0.1 mg/mL or 0.3 nM in normal plasma 19 ) does not preclude a large escape of FVIII-specific CD4 T cells from negative thymic selection. Whether such a large pool of circulating FVIII-specific CD4 T cells provides help to natural FVIII-specific B cells and accounts for the presence of natural anti-FVIII antibodies in a substantial percentage of healthy individuals 3,20 and whether the uncontrolled recruitment of this pool leads to the development of acquired hemophilia remain to be established.…”

Factor VIII inhibitors: von Willebrand factor makes a difference in vitro and in vivo

“…Previous studies have shown that VWF in the FVIII‐deficient plasmas utilized in one‐stage aPTT assays appears to depress measurements of apparent FVIII activity [23–25]. We wanted to determine whether similar effects were present when inhibitor titers were calculated using a chromogenic assay to measure residual FVIII activity.…”