ABSTRACT
We report the results of external quality assessment exercises in which 60 to 120
centers performed factor VIII (FVIII) inhibitor testing on a series of samples over
a 13-year period. Samples from seven different subjects were distributed for analysis
comprising the following: four different subjects with severe hemophilia A with antibodies
following replacement therapy, one subject with acquired hemophilia A and antibodies
to FVIII, one subject with normal FVIII and an easily detected lupus anticoagulant,
and one subject with mild hemophilia A and a difficult-to-detect lupus anticoagulant
but without antibodies to FVIII. In all of the surveys the results obtained in different
centers analyzing the same sample varied to an extent that would influence patient
management decisions. In the UK National External Quality Assessment Scheme surveys
reported here, there was considerable interlaboratory variation in the results of
FVIII inhibitor testing that did not improve over the survey period. The coefficient
of variation of results in different centers was between 33% and 106% in samples from
patients with severe congenital hemophilia A. In some cases, results were affected
by assay components. For one plasma, the mean FVIII inhibitor results in centers using
one source of normal plasma was 3.9 Bethesda unit (BU)/mL compared with a mean of
5.7 BU/mL in centers using a different normal plasma source (p = 0.04). Our data indicate that the detection of FVIII inhibitors is not the same
in different centers, and the degree of variability noted makes it likely that assay
variability has contributed to the lack of international consensus in relation to
the real incidence of FVIII inhibitors in different clinical settings. Improvements
in assay standardization are urgently needed.
KEYWORDS
FVIII inhibitor - quality assurance
REFERENCES
Available at: http://www.wfh.org/2/docs/Publications/Diagnosis_and_Treatment/Lab_manual_web.pdf Accessed December 7, 2009
steve.kitchen@sth.nhs.uk
