title: Identification of factor inhibitors by diagnostic haemostasis laboratories: a large multi-centre evaluation.
abstract: We have assessed the proficiency of diagnostic haemostasis facilities to correctly identify coagulation factor abnormalities and inhibitors. Forty-two laboratories participating in the external Quality Assurance Program (QAP) conducted by the RCPA agreed to participate and were each sent a set of eight samples (each 3 x 1 ml) for evaluation. They were asked to blind test these samples for the presence or absence of inhibitors, and where identified, to perform further analysis (including specific inhibitor analysis). In order to make the exercise more challenging, in addition to true factor inhibitors, samples were provided that reflected potential pre-analytical variables that might arise and complicate inhibitor detection or lead to false inhibitor identification. In brief, the sample set comprised a true high level factor (F) V inhibitor, a true moderate level FVIII inhibitor (but sample was defibrinogenated), a true lupus anticoagulant (LA), a normal (but slightly aged) plasma sample, a normal serum sample, a normal EDTA sample, an oral anticoagulant/vitamin K deficiency sample, and a gross heparin ( approximately 10 U/ml) contaminated sample. Sixty-three percent of participants correctly identified the true FV inhibitor as such, although the reported range varied greatly [10 to >250 Bethesda units (BU/ml)] and 46% correctly identified the true FVIII inhibitor, despite the complication of the sample presentation, although the reported range also varied (7 to 64 BU/ml). Some laboratories either failed to identify the inhibitor present, or misidentified the inhibitor type. The LA, the oral anticoagulant/vitamin K deficiency, the normal serum sample, and the normal (aged) sample were also correctly identified by most laboratories, as was the absence of specific factor inhibitors in these samples. However, a small subset of laboratories incorrectly identified the presence of specific factor inhibitors in some of these samples. The heparin sample was also correctly identified by most (68%) laboratories. In contrast, the normal EDTA sample was misidentified as a FV and/or FVIII inhibitor by most (68%) laboratories, and only one laboratory correctly identified this as an EDTA sample. Thus, we conclude that although laboratories are able, in most cases, to identify the presence of true factor inhibitors, there is a large variation in identified inhibitor levels and there are also some significant errors in identification (i.e. false negatives and misidentifications). In addition, there is a significant false positive error rate where some laboratories will identify the presence of specific factor inhibitors where no such inhibitor exists (i.e. false positives).
authors.affiliation: Department of Haematology and RCPA Quality Assurance Program (QAP), Institute of Clinical Pathology and Medical Research (ICPMR),Westmead Hospital, Westmead, New South Wales, Australia. emmanuel@icpmr.wsahs.nsw.gov.au
authors.forename: Emmanuel J
authors.initials: EJ
authors.lastname: Favaloro
authors.forename: Roslyn
authors.initials: R
authors.lastname: Bonar
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Duncan
authors.forename: Gail
authors.initials: G
authors.lastname: Earl
authors.forename: Joyce
authors.initials: J
authors.lastname: Low
authors.forename: Margaret
authors.initials: M
authors.lastname: Aboud
authors.forename: Sarah
authors.initials: S
authors.lastname: Just
authors.forename: John
authors.initials: J
authors.lastname: Sioufi
authors.forename: Alison
authors.initials: A
authors.lastname: Street
authors.forename: Katherine
authors.initials: K
authors.lastname: Marsden
mesh_terms: D001779:Blood Coagulation Factors / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000276:immunology; D019411:Clinical Laboratory Techniques / Q000592:standards*; D003951:Diagnostic Errors; D004492:Edetic Acid / Q000032:analysis; D005165:Factor V / Q000037:antagonists & inhibitors; D005169:Factor VIII / Q000037:antagonists & inhibitors; D006487:Hemostasis; D006801:Humans; D011785:Quality Assurance, Health Care / Q000592:standards; D015203:Reproducibility of Results
chemical_list: D001779:Blood Coagulation Factors; D005165:Factor V; D005169:Factor VIII; D004492:Edetic Acid