Factor VIII assay variability in postinfusion samples containing full length and B-domain deleted FVIII.

INTRODUCTION: Although the variability in factor VIII (FVIII):C measurement is well recognized, this has not been widely reported for post-FVIII infusion samples. AIM/METHODS: Three samples from haemophilia A patients were distributed in a UK National External Quality Assessment Scheme survey, each after treatment with either ReFacto AF, Kogenate FS or Advate. Fifty-two UK haemophilia centres performed FVIII assays using one-stage (n = 46) and chromogenic (n = 10) assays. Centres calibrated assays with the local plasma standard and with ReFacto AF laboratory standard for the ReFacto AF sample. RESULTS/CONCLUSIONS: Chromogenic assays gave significantly higher results than one-stage assays (P < 0.0001, 32% difference) in the post-Kogenate sample but not in the post-ReFacto AF (11% higher by chromogenic assay, ns) or post-Advate samples (3% lower by chromogenic, ns) when assays were calibrated with plasma standards. Twenty centres used all Instrumentation Laboratory (IL)-activated partial thromboplastin time reagents (Synthasil)/IL deficient plasma/reference plasma) in the one-stage assay and 15 used all Siemens reagents (Actin FS/Siemens deficient plasma/reference plasma); this made a significant difference to results post-ReFacto AF (41% higher by IL reagents, P < 0.0001) and Advate (39% higher by IL reagents, P < 0.0001), but not Kogenate (7% higher by IL, ns) when calibrated with plasma standards. Differences between results obtained with different one-stage assay reagents for monitoring Advate have implications for dosing patients. Furthermore, there was considerable inter-laboratory variation as indicated by CVs in the range 15-26% for chromogenic assay and 12-19% for one-stage assay results. This study suggests that external quality assessment schemes should offer participation in post-FVIII infusion schemes where haemophilic patients are monitored.

Stability of coagulation proteins in lyophilized plasma.

INTRODUCTION: External quality assessment (EQA) is an important component of quality assurance for laboratory tests of haemostasis. Lyophilization of plasma confers stability of labile clotting factors, allowing valid comparison of results between participating centres. However, elevated ambient temperatures in some geographical areas could affect the stability of lyophilized samples in transit. METHODS: The effect on lyophilized plasma samples of consistent elevated temperature with respect to haemostasis tests was determined in a single centre. The temperature to which packages were exposed during transit was also monitored. RESULTS: Survey packages were exposed to average temperatures up to 31.9 °C and maximum temperatures up to 39.7 °C over delivery periods between 1 and 8 weeks. In-house studies revealed samples to be stable over a 6-week period at a constant 30 °C, and only small changes were observed for samples exposed to 37 °C for 4 weeks. 6-week storage at 37 °C was associated with average changes of up to 15% in factor assay activity. CONCLUSION: Lyophilized EQA material employed in UK NEQAS surveys is stable under conditions encountered for the majority of participants, but in cases of delayed delivery of samples, the effect of temperature on sample integrity must be considered when assessing laboratory performance.

Investigation of a prolonged APTT. Different approaches taken by laboratories to achieve the same diagnosis.

INTRODUCTION: The APTT is widely employed as part of a coagulation screening panel, used as a pre-operative assessment of bleeding risk, to detect hereditary and acquired haemostatic defects and to monitor anticoagulant therapy. External quality assessment (EQA) exercises assess laboratory performance of individual tests, but rarely assess the approach to investigation of an abnormal result. METHODS: A multicentre exercise was carried out to investigate the ability of laboratories to identify the cause of a prolonged APTT. A sample was distributed with a request to carry out whichever tests were considered necessary to achieve a probable diagnosis. RESULTS: One hundred and ten centres in the UK NEQAS programme took part, and all 104 centres providing an interpretation correctly identified deficiency of FVIII in the sample. However, of these, 10 centres reported additional defects, including lupus anticoagulant, FIX deficiency, FXII deficiency and a FVIII inhibitor. CONCLUSIONS: A markedly varied approach to investigation of a prolonged APTT was observed, although a lack of clinical information may have contributed to this finding.

Laboratory performance in the World Federation of Hemophilia EQA programme, 2003-2008.

External quality assessment (EQA) has been shown to improve laboratory performance and diagnosis in haemostasis. We report here findings from the World Federation of Haemophilia (WFH) EQA programme during the period 2004-2007. Samples for PT, APTT, FVIII:C, FIX:C and VWF assays were distributed to centres in both established and emerging countries, and results were compared with results obtained by United Kingdom National External Quality Assessment Scheme (UK NEQAS) participants on the same samples. In general, good agreement was seen throughout between WFH and UK NEQAS for screening tests, and it was possible to identify an improvement in WFH centre agreement for results for VWF assays during the period of study. Agreement between emerging and established WFH centres was comparable for screening tests, possibly indicative of the relative simplicity of these tests and the degree of automation now employed in almost all haemostasis laboratories. However, CVs and performance compared with UK NEQAS participant results for factor assays amongst established centres was better than between emerging centres. Distribution of a questionnaire revealed different application of methodology for these assays, which may contribute to the observed difference in performance. Several centres participated in supplementary exercises, with comparable results obtained by emerging and established centres performing FVIII and fibrinogen measurement on cryoprecipitate, and all centres performing FVIII inhibitor assays correctly identifying the presence of an inhibitor. Participation in EQA programmes should continue to encourage improvement in laboratory performance and therefore improvements in the diagnosis and care of patients with haemophilia.

Patient self-management of oral anticoagulation and external quality assessment procedures.

The role of external quality assessment (EQA) is a contentious issue for patient self-management (PSM) of oral anticoagulation. Patients from general practices in the West Midlands undertaking PSM were recruited to compare efficacy of patients' and health professionals' EQA procedure using the UK National External Quality Assessment Scheme (NEQAS). Patients using Coaguchek (Roche Diagnostics) were trained to perform EQA as part of their PSM training. They undertook PSM for 26 weeks and were asked to perform EQA using material provided by the UK NEQAS twice at home without supervision and twice at the practice with supervision. Patients' results were compared with health care professional users of Coaguchek S. Twenty-three PSM patients were compared with 75 health care professional users of the NEQAS scheme. The PSM group international normalized ratio (INR) percentage time in range was 74%. There was no significant difference in the median results on NEQAS samples obtained by the patients and those obtained by professionals. Three patients were outwith consensus (results > 15% from the median INR) on more than one occasion. Patients were able to perform the EQA tests competently. The data show that good agreement can be achieved between patients analysing the same EQA samples, with coefficients of variation ranging from 22.3% to as low as 5.4%. Further study is required to determine how precision within these EQA schemes relates to the stability of treatment in patients' management of their own anticoagulation.