Laboratory diagnosis of hereditary bleeding disorders: external quality assessment

A World Federation of Hemophilia external quality assessment scheme has been established to promote high standards of laboratory performance in haemophilia centres world-wide. Results from 22 International Haemophilia Training Centres (IHTCs) provide target values for the prothrombin time (PT), activated partial thromboplastin time (APTT), factor VIII:C, IX:C and von Willebrand factor assays, against which the performance of haemophilia centres (HCs) in developing countries can be assessed. A higher proportion of HCs failed to identify an abnormal PT or APTT in samples from donors with mild deficiencies of the extrinsic and intrinsic systems, respectively. For factor VIII:C and IX:C assays, agreement between HC results was consistently poorer than between IHTCs. However, improvement in between-centre agreement could be seen for two samples distributed on more than one occasion. A minority of HCs perform assays for von Willebrand factor, and a questionnaire revealed equipment and reagent costs as limiting the range of assays which could be carried out in several centres. However, agreement was in some cases better between those HCs that did perform VWF assays, than between IHTCs. The problems of screening test sensitivity, and between-centre agreement for factor assays need to be addressed, together with the limitations which prevent HCs from performing a full range of tests in the diagnosis and treatment of bleeding disorders.