Potential misdiagnosis of dysfibrinogenaemia: Data from multicentre studies amongst UK NEQAS and PRO-RBDD project laboratories.

INTRODUCTION: Mutations in fibrinogen (Fgn) genes, causing dysfibrinogenaemia, can result in either a bleeding or thrombophilic diathesis. Dysfibrinogenaemia is infrequently encountered in hospital laboratories, and the utility of different assays in the diagnosis of dysfibrinogenaemia has not previously been explored in a multicentre study. We describe here an exercise in which PRO-RBDD project (prospective data collection on patients with fibrinogen and Factor XIII deficiencies) centres, and UK NEQAS centres, performed investigations for dysfibrinogenaemia.

METHODS: Samples from donors with dysfibrinogenaemia (sample 1: gamma p.Arg301Cys, sample 2: Bbeta166Arg3Cys-Fgn Longmont, sample 3: Aalpha p.Arg35His) and a normal donor were sent to laboratories for investigation for possible dysfibrinogenaemia. Median, coefficient of variation and range were determined for each assay method.

RESULTS: Results were returned from 62 UK NEQAS and 24 PRO-RBDD centres. PT, APTT, Clauss fibrinogen and thrombin times were performed by >90% of centres, with 51% performing reptilase times, and 31% fibrinogen antigen. All centres identified samples 1 and 3 as abnormal. However, 39% of centres reported a normal or raised fibrinogen for the Fgn Longmont sample, and marked differences in Clauss fibrinogen results with different reagents were noted for this sample (median 1.01 g/L vs 5.10 g/L for the two mostly widely used reagents).

CONCLUSION: In-house studies suggest that the method of detection of fibrin clot formation may result in different Clauss fibrinogen measurements with FgnLongmont plasma. It is possible that some widely used methodologies, both using optical and mechanical end-point detection systems, will fail to detect this rare fibrinogen variant.