Factor VIII/IX inhibitor testing practices in the United Kingdom: Results of a UKHCDO and UKNEQAS national survey.

INTRODUCTION: Inhibitor formation is the greatest challenge facing persons with haemophilia treated with factor concentrates. The gold standard testing methodologies are the Nijmegen-Bethesda assay (NBA) for FVIII and Bethesda assay (BA) for FIX inhibitors, which are affected by pre-analytical and inter-laboratory variability. AIMS: To evaluate inhibitor testing methodology and assess correlation between self-reported and actual methodology. METHODS: Methodology was evaluated using a survey distributed alongside a UK National External Quality Assessment Service Blood Coagulation external quality assurance (EQA) exercise for FVIII and FIX inhibitor testing. RESULTS: Seventy four survey and EQA exercise responses were received (response rate 63.2%), with 50 paired survey/EQA results. 47.1% (33/70) reported using the NBA and 42.9% (30/70) the BA for FVIII inhibitor testing. Review of FVIII inhibitor assay methodology demonstrated discrepancy (self-reported to actual) in 64.3% (BA reporting) and 27.6% (NBA reporting). Pre-analytical heat treatment was used by 32.4%, most commonly 56°C for 30 minutes. Assay cut-offs of 0.1-1.0 BU/mL were reported. EQA samples (acquired FVIII and congenital FIX) demonstrated titres and coefficients of variation (CV) of 3.1 BU/mL (0.7-15.4 BU/mL; CV = 43%) and 18.0 BU/mL (0-117 BU/mL; CV = 33%), respectively. No significant assay or laboratory factors were found to explain this variance, which could have resulted in change in management for 6 patients (5 misclassified high-titre FVIII inhibitors and 1 false negative for a FIX inhibitor). CONCLUSIONS: Heterogeneity was seen at each stage of assay methodology. No assay-related factors were found to explain variation in inhibitor titres. Further standardization is required to improve inhibitor quantification to guide patient care.

Postpartum bleeding in women with inherited bleeding disorders: a matched cohort study.

: Women with inherited bleeding disorders (IBDs) are reported to have higher rates of primary and secondary postpartum haemorrhage (PPH), even with optimal haemostatic management. We evaluated whether women with IBD have higher odds of PPH compared with those without, when controlled for mode of delivery with a control group of women without IBDs. The obstetric experiences and outcomes of all women with IBD delivering at a tertiary centre between 2008 and 2017, were compared with matched controls (1 : 1). Obstetric care was provided according to national guidelines to both women with IBD and controls. Primary PPH was defined as estimated blood loss at least 500 ml. There were 46 completed pregnancies in women with IBD: 16 haemophilia A carriers, eight haemophilia B carriers, eight factor XI deficiency patients and 14 von Willebrand disease patients (type 1 = 6; type 2 = 8). No peripartum haemostatic treatment was received by carriers of haemophilia A or B. There were 74 control pregnancies. Women with IBD had higher odds of primary PPH, in a model controlling for mode of anaesthesia (adjusted odds ratio 5.30, 95% confidence interval 1.02-27.59, P = 0.048). Carriers of haemophilia A had a higher, statistically nonsignificant, odds for primary PPH than controls (adjusted odds ratio 6.85, confidence interval 0.77-60.73, P = 0.084). An increase in primary PPH was observed in women with IBD, particularly in haemophilia A, despite management according to guidelines. These results warrant further investigation and consideration should be given as to which factor levels to target.