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A novel specific immunoassay for plasma two-chain factor VIIa:
investigation of FVIIa levels in normal individuals and in patients with
acute coronary syndromes
H Philippou, A Adami, RA Amersey, PJ Stubbs and DA Lane
Department of Haematology, Charing Cross and Westminster Medical School,
London, UK.
We report the development of an enzyme-linked immunosorbent assay (ELISA)
that is specific for factor VIIa (FVIIa). This assay uses a neoantigen
specific capture antibody directed to the amino acid peptide sequence N
terminal to the FVII cleavage activation site. The antibody exhibits
approximately 3,000-fold greater reactivity to FVIIa than FVII on a molar
basis. Experiments using plasma with added (exogenous) human FVIIa gave
quantitative recovery in the ELISA over a range of 0.20 to 3.2 ng/mL of
FVIIa. The intra- and inter-assay coefficient of variation (CVs) of the
ELISA are 4.5% and 9.8%, respectively. The ELISA shows excellent
correlation (r = .99) with a functional assay (using recombinant soluble
tissue factor) in detecting FVIIa added to plasma over the range 0.05 to
18.0 ng/mL. However, a major discrepancy exists between the two assays when
normal endogenous plasma concentrations of FVIIa are measured. Using normal
plasma (n = 14) the functional assay reported 3.10 +/- 0.30 ng/mL (mean +/-
SE) whereas only 0.025 +/- 0.010 ng/mL was detected in the same samples by
the immunoassay. Patients (n = 43) presenting with acute coronary syndromes
(myocardial infarction and unstable angina) exhibited elevations (P <
.05) in immunologically detected FVIIa, 0.093 +/- 0.013 ng/mL (mean +/- SE)
compared to patient controls (n = 20) contemporaneously admitted with
noncardiac chest pain, 0.048 +/- 0.007 ng/mL (mean +/- SE). These
elevations in the acute coronary syndromes were accompanied by increased (P
< .05) and correlating prothrombin fragment F1 + 2 levels (Spearman
correlation coefficient rs = .4, P < .01), demonstrating that thrombin
generation is certainly associated with, and may even be caused by,
extrinsic pathway activation.
Volume 89,
Issue 3,
pp. 767-775,
02/01/1997
Copyright © 1997 by The American Society of Hematology
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