RESUMEN
AIMS: To assess international and local trends in laboratory testing for activated protein C (APC) resistance (APCR) and factor V Leiden (FVL). Also, to compare local results of FVL testing with a variety of different clot-based APCR assays to assess utility for detection of APCR both related and unrelated to FVL. METHODS: Local test statistics and test result patterns were evaluated and international literature was reviewed over the past 9 years. Direct comparisons of FVL testing by DNA analysis against (a) the standard APTT-based APCR assay, with and without pre-dilution with factor V deficient (FVD) plasma, or with and without normalisation, and (b) three alternative RVVT-based procedures (most recently using a commercial RVVT-based procedure called GradiLeiden V; GLV). In total, data obtained over the past 7 years, using referred samples from over 1,000 patients, have been assessed. RESULTS: The 9-year retrospective assessment has seen many changes in test-based processes. Locally, test requests for both APCR and FVL have consistently increased. We suspect this has been fuelled in part by media reports of 'economy class syndrome' (ECS) and associated general public and clinical concern. Current request patterns number around 800 APCR and 1,600 FVL per year. Interestingly, most requests are for one or either test, with joint requests comprising less than 20% of those overall. Although test requests are increasing, detection of the FVL defect as a proportion of test requests is actually falling (from a high of over 25% in 1996 to around 14% currently). Whether this suggests an increasing tendency for clinical ordering in the absence of appropriate clinical histories is a matter of concern. Consistent with previous findings, the original and commonly used APTT-based procedure was found to show the least correlation with DNA findings, with a large overlap between FVL and non-FVL individuals. The alternate-RVVT-based procedures showed much better differentiation. Thus, for the APTT-based method, in order to ensure 100% sensitivity, an APC ratio cut-off value of 3.1 was required, and this yielded only 49.1% specificity. In contrast, for the GLV RVVT-based method, in order to ensure 100% sensitivity, an APC ratio cut-off value of 1.65 was required, and this yielded 96.6% specificity. CONCLUSIONS: It is important to recognise the limitation of APTT-based assays to discriminate FVL. However, a combination of RVVT- and APTT-based testing is still recommended, as this will provide excellent discriminatory power for the FVL defect, particularly negative prediction, in addition to detection of potential APCR unrelated to FVL, as well as detection of other potential haemostatic disturbances. Accordingly, we detail strategies, including a test algorithm that we are currently using to improve our detection of APCR and prediction of FVL, and use of clotting-based procedures as the first-line approach.
Asunto(s)
Resistencia a la Proteína C Activada/diagnóstico , Ciencia del Laboratorio Clínico/normas , Ciencia del Laboratorio Clínico/tendencias , Trombofilia/diagnóstico , ADN/análisis , Factor V/análisis , Factor V/genética , Humanos , Tiempo de Tromboplastina Parcial , Tiempo de Protrombina , Estudios RetrospectivosRESUMEN
Five expert laboratories have participated in a cross-laboratory study to co-evaluate and compare three commercial Factor VIII/von Willebrand factor (VWF) concentrates. A total of nine factor concentrate lots were evaluated, comprising AHF (High Purity) (AHF HP; x3), Biostate (x3) and Humate/Haemate (x3). All laboratories blind tested for FVIII: C, VWF: Ag and VWF: CB, four tested for VWF: RCo, and one performed VWF: Multimers. The study yielded inter-laboratory CVs for VWF: Ag and FVIII:C around 10-15%, and for VWF:CB and VWF:RCo around 20%, significantly lower than those of previous multi-laboratory surveys. All three lots of AHF HP contained in the vicinity of 25 U/ml FVIII:C, around 60-75 U/ml of VWF:Ag, but only 30-45 U/ml of VWF:CB and 40-50 U/ml of VWF:RCo (thus, CB/Ag ratio around 0.5-0.6 and RCo/Ag ratio around 0.6-0.7). Study determined that FVIII: C and VWF: RCo levels were similar to manufacturer assigned levels. Some loss of the high molecular weight (HMW) multimers was observed, together with an intense low molecular weight (LMW) VWF band consistent with some reduction or proteolysis of HMW VWF. All three lots of Humate/Haemate contained in the vicinity of 23-32 U/ml of FVIII:C, 70-105 U/ml of VWF: Ag, 50-90 U/ml of VWF: CB and VWF: RCo (i.e. CB/Ag ratio around 0.6-0.9 and RCo/Ag ratio around 0.6-1.1). Study-determined FVIII: C and VWF: RCo levels were similar to manufacturer-assigned levels. The LMW multimer band seen with AHF HP was also observed with Humate/Haemate. All three lots of Biostate contained in the vicinity of 40-55 U/ml of FVIII:C, 105-170 U/ml of VWF:Ag, 90-150 U/ml of VWF:CB, and 90-135 U/ml of VWF:RCo (i.e. CB/Ag and RCo/Ag ratios around 0.7-1.0). Study-determined FVIII:C levels were similar to manufacturer-assigned levels. The LMW multimer band seen with AHF HP was not observed with Biostate. The defined pattern of increasing CB/ Ag from AHF HP to Humate/Haemate and Biostate was consistently observed in study data from each of the five laboratories. In conclusion, study findings indicate some differences in the retention of functional/ HMW VWF between factor concentrates, and this is expected to have significant implications in terms of clinical efficacy for therapy in VWD.