Assay discrepancy in factor VIII activity between the one-stage and the chromogenic assays has been described in approximately one third of patients with non-severe haemophilia A. Whether assay discrepancy may also occur in patients with haemophilia B remains unknown.
Aim
This study compared the results from the one-stage and the chromogenic assays in patients with haemophilia B.
Methods
Plasma samples from patients with haemophilia B attending the haemophilia centre in Malmö, Sweden, were collected after a wash-out period of more than 7 days and analysed with both assays.
Results
Fifty samples from 36 patients were analysed. No discrepancy was found in patients with severe haemophilia B. Among the 44 plasma samples from patients with non-severe disease, 15 showed a twofold or greater difference between the results of the two methods, with the chromogenic method presenting the higher value (mean FIX:Cone-stage0.02 vs. FIX:Cchromo 0.06 IU mL−1). Of these 15 samples, 14 were from seven individuals from five families with the same mutated amino acid at the N-terminal cleaving site of the activation peptide (FIX: c.572G>A; p.Arg191His or FIX: c.571C>T; p.Arg191Cys). These mutations were not observed in any patients with non-discrepant results. The reported bleeding frequency for these patients was low and indicative of a mild bleeding phenotype.
Conclusion
Our findings imply that assay discrepancy occurs for factor IX activity and that both type of assays are needed for a correct diagnosis and classification of haemophilia B. The underlying mechanism by which the mutation influences the assays remains to be determined.
# 36명의 환자로 부터 50개의 샘플을 검사.
# 중증환자가 아닌 샘플44개 중 15개 샘플이 Chromogenic Assay가 2배이상 높게 나옴.
이 15개 샘플 중 14개의 변이가 동일한 돌연변이(FIX: c.572G>A; p.Arg191His or FIX: c.571C>T; p.Arg191Cys). 이 환자들은 출혈빈도가 낮았음
# HA와 마찬가지로 9인자 활성도가 검사 방법에 따라 불일치가 발생함. 정확한 진단을 위해서는 두 가지 검사방법이 필요함.
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