Prospective evaluation of automatized PF4/heparin immunoassays HemosIL HIT-ab (PF4-H) for the diagnosis of heparin-induced thrombocytopenia.

INTRODUCTION: Recently, rapid immunoassays have been developed to allow the detection of antibodies anti-PF4/heparin. In this prospective study, we evaluated the performances of a automatized immunoassay (HemosIL HIT-Ab) in comparison with an ELISA (Zymutest HIA IgG) used for the diagnosis of heparin-induced thrombocytopenia (HIT) in association with the 4T's score. METHODS: According to the 4T's score, samples with score ≤3 had no further analysis. Two immunological assays Zymutest HIA IgG and HemosIL HIT-Ab were performed in samples with score ≥4. In patients with at least one positive immunological assay or two negative immunological assays but with high-pretest probability (4T's score ≥6), HIT was screened by one functional assay using washed platelets. RESULTS: The sensitivities of both assays were excellent and comparable (100%). The specificity was 92.3% for ELISA and 91.2% for HemosIL HIT-Ab. The analysis of the operating characteristics showed that both assays have almost identical ROCs (AUROC, 0.9951 and 0.9853, respectively, for ELISA and HemosIL HIT-Ab) and the calculating of the κ coefficient revealed a good agreement (0.67). CONCLUSION: Performance characteristics of the HemosIL HIT-Ab are comparable to the Zymutest HIA IgG. The HemosIL HIT-Ab can be used in association with the 4T's score to rule out HIT.

Does the presence of von Willebrand factor in FVIII-deficient plasma influences the measurement of FVIII inhibitor titres in haemophilia A patients?

INTRODUCTION: Reliable measurement of FVIII inhibitor is critical in the follow-up of haemophilia A patients. We performed a multicentre study to evaluate whether the presence of von Willebrand factor (VWF) in FVIII-deficient plasma (FVIII-DP) influences FVIII inhibitor titres. METHODS: Six French haematology laboratories participated in this study. Three samples with varying FVIII inhibitor titres (1, 5 and 15 BU/mL) and one sample without any detectable FVIII inhibitor were tested using four different procedures for FVIII inhibitor assay. The Nijmegen method and a modified assay with imidazole were performed using FVIII-DP with and without VWF in the control mixture and as substrate plasma in the FVIII one stage assay (OSA). Each mixture (reference and test) was incubated for two hours at 37 °C with buffered normal pool plasma. RESULTS: Higher inhibitor titres were measured in 5 and 15 BU/mL samples when assays were performed with the Nijmegen method and FVIII-DP without VWF. When samples were diluted in imidazole buffer, similar inhibitor titres, close to expected values, were measured whether VWF was present in the FVIII-DP or not. The data obtained were also more accurate when residual FVIII activity levels between 40% and 60% were used to calculate inhibitor titres, despite a linear type I reaction kinetics. CONCLUSION: These results support the hypothesis that reliable FVIII inhibitor titres can be measured without the use of FVIII-DP containing VWF when an imidazole-modified assay is used.

The use of the new ReFacto AF Laboratory Standard allows reliable measurement of FVIII:C levels in ReFacto AF mock plasma samples by a one-stage clotting assay.

Factor VIII coagulant (FVIII:C) levels measured in patients receiving ReFacto® (B-domain-deleted recombinant FVIII) using chromogenic substrate assay (CSA) and one-stage clotting assay (OSA) have frequently shown discrepancies, and the use of the ReFacto Laboratory Standard (RLS) has therefore been recommended to minimize these differences. The potency of ReFacto AF®, the albumin-free successor of ReFacto®, is determined using CSA for the titration of vials, and a new standard (RLS-AF) was developed to measure its biological efficacy using OSA. This multicentre study therefore evaluated the efficacy of this new RLS in minimizing differences between OSA and CSA when measuring FVIII:C levels in plasma. Mock plasma samples were prepared by diluting ReFacto AF® in FVIII-deficient plasma to obtain four concentrations ranging from 15 to 90 IU dL⁻¹ . FVIII:C levels were then measured in six laboratories on four separate days using three different procedures, i.e. OSA with a plasma standard (PS) as reference, OSA with RLS-AF and CSA with PS. The inter-centre standard deviation ranged from 1.4 to 5.5 IU dL⁻¹. However, FVIII:C levels measured with OSA were closer to the expected values when RLS-AF was used. In addition, the uncertainty of measurement, reflecting the inter-method discrepancy was greatly reduced when RLS-AF was employed in OSA (15%) in place of PS (33%). This study demonstrates that the OSA performed with RLS-AF to establish calibration curves provides a valuable alternative to CSA to measure FVIII:C in ReFacto-AF-treated patients.

Adaptability of protein A-immunoadsorption allows temporary reduction of anti-VIII antibodies and realisation of high-risk haemorrhagic surgery.

We report the successful treatment by protein A-immunoadsorption (IA) of an hemophilic man with anti-F VIII antibodies (Abs) who needed high-risk bleeding surgery. This patient had developed high levels of anti-F VIII Abs preventing substitution by clotting factor and preventing high-risk bleeding surgery. Because of rebound in Abs levels or complications, IA procedures were modified several times leading to appropriate decrease of anti-F VIII inhibitor Abs allowing bilateral knees surgery. IA procedure is enough adaptable to be modified to prevent complications. Collaboration between clinical, biological, apheresis and surgical teams implied has permitted surgery and prevented life-threatening bleeding complications.

[The abnormal activated partial thromboplastin time biphasic waveform: a red flag in the sepsis? Technique and interest as marker of the sepsis]. / Le Flag A2: un drapeau rouge dans le sepsis? Rappel technique et intérêt comme marqueur du sepsis.

The biphasic waveform (BPW) is an abnormality of the optical transmission waveform obtained during measurement of the activated partial thromboplastin time on a specific photometric haemostasis autoanalyzer. This abnormality is related to calcium-dependent formation of complexes between C reactive protein and very low density lipoprotein. Biphasic waveform had a high sensitivity and negative predictive value for the identification of patients with severe sepsis and septic shock. On day 3, the time course of the biphasic waveform is a marker for the prognosis of sepsis-related mortality. The BPW is not a surrogate marker for C-reactive protein or procalcitonin and provides additional information. Further trials should be necessary using BPW for diagnostic and management procedures. Compared with other laboratory markers such as C reactive protein or procalcitonin, activated partial thromboplastin time waveform analysis is a tool that is rapid, inexpensive, effective and available 24 hours a day. When the analyzer is locally available, waveform analysis of this routine coagulation test provides information for the diagnosis of severe sepsis and the prognosis of septic patients.

Human plasma fibrinogen measurement derived from activated partial thromboplastin time clot formation.

Prothrombin time-derived measurement of fibrinogen (PTd) has already been described. Activated partial thromboplastin time-derived measurement of fibrinogen (aPTTd) has not yet been clearly defined. Using an MDA II coagulometer (Organon Teknika, Durham, North Carolina, USA), we have therefore compared fibrinogen levels determined with Clauss, PTd, and aPTTd assays and an enzyme immunoassay (EIA) in 172 samples. Of these, 47 were from pre-operative controls, 18 from patients with liver disease, 28 from patients with hyperfibrinogenaemia, 33 from patients treated with vitamin K antagonists, 22 from patients treated with unfractionated heparin and 24 from haemophilic patients. Within the normal range, interassay and intra-assay variations were comparable. For control samples, PTd, aPTTd and Clauss assays were well correlated, without any systematic error. EIA was also correlated but values were slightly higher (mean of difference = 0.24). Pathological samples showed an overestimation of fibrinogen when using PTd measurements in patients treated with vitamin K antagonists, as well as when using aPTTd measurements in patients presenting with factor VIII and factor IX deficiencies. These results indicate that, despite expected financial savings, aPTTd fibrinogen measurements should not be used without restriction. PTd and aPTTd fibrinogen determinations are provided without any additional cost. Their comparison with Clauss fibrinogen results may constitute a validation tool or have additional diagnostic utility (e.g. identifying polymerization abnormalities in case of dissimilar results).

Factor IX gene analysis in 70 unrelated patients with haemophilia B: description of 13 new mutations.

Seventy unrelated patients suffering from haemophilia B have been screened for determining the molecular defect and for evaluating the spectrum of factor IX mutations in the Rhône Alpes region in France. Most patients were characterized with respect to factor IX antigen and factor IX coagulant activity. We have used denaturing gradient gel electrophoresis to obtain a full scanning of the whole coding, promoter, and exon flanking sequences of the factor IX gene. This technique enabled us to determine the molecular defect in 68 out of 70 families (97%), and the mutation was further identified in the two last patients with a direct sequencing of the gene. A total of 2 complete gene deletions in patients with antifactor IX inhibitor, 6 small insertions/deletions and 62 point mutations were found. Two of these nucleotide substitutions (Arg145His and Ala233Thr) were detected in 21 patients (30%) suggesting the existence of a local founder effect. Thirteen mutations were previously undescribed, including 7 missense mutations. The detection of mutations in patients affected with haemophilia B may shed some light in the structure-function relationship of factor IX molecule within the coagulation system.