Discrepant low von Willebrand factor activity results on the ACL TOP analyzer are frequent in unselected patients with myeloproliferative neoplasms and show no correlation with high-molecular-weight multimer loss or bleeding phenotype.

BACKGROUND: Bleeding complications are common in patients with myeloproliferative neoplasms (MPNs), with a subset developing acquired von Willebrand disease. Despite this association, a wide spectrum of von Willebrand factor (VWF) abnormalities are described, and the performance of modern assays remains unclear. OBJECTIVES: To comprehensively describe the pattern of VWF laboratory abnormalities in the MPN population. METHODS: We collected samples from 74 unselected clinic patients with MPNs to evaluate VWF quantitatively and qualitatively via multiple methods, correlating findings with a retrospective analysis of clinical bleeding data. VWF assays were performed on both ACL TOP (Instrumentation Laboratory) and Acustar (Instrumentation Laboratory) analyzers using HemosIL reagents (Instrumentation Laboratory), along with multimer analysis by gel electrophoresis. RESULTS: Functional VWF measurements were not concordant between assays, with a median ACL TOP VWF glycoprotein IbR to antigen ratio (VWF:GPIbR/VWF:Ag) of 0.57 (IQR, 0.43-0.71) compared to a median Acustar VWF:GPIbR/VWF:Ag of 0.91 (IQR: 0.82-1.03;P < .001). The ACL TOP showed disproportionately lower results, with 73% of patients having a ratio <0.7. Despite this, no patient experienced loss of high-molecular-weight multimers by gel electrophoresis. An inverse relationship was observed between platelet count and functional ratios on both ACL TOP (R2 = 0.20; P < .001) and Acustar (R2 = 0.18; P = .0011) analyzers. While clinically significant bleeding events were relatively common (11% patients), there was no association with VWF assay abnormalities, and generally, an alternate cause(s) was identified. CONCLUSION: Discrepancies in functional VWF assays are common in patients with MPN, particularly by ACL TOP VWF:GPIbR. Based on our limited series, a VWF functional to an antigenic ratio of <0.7 ("type 2 pattern") alone is poorly predictive of bleeding risk.

A multicentre assessment of contemporary laboratory assays for heparin induced thrombocytopenia.

Heparin induced thrombocytopenia (HIT) is a rare but potentially fatal complication of heparin therapy. In some patients, HIT causes platelet activation and thrombosis (sometimes abbreviated HITT), which leads to adverse clinical sequalae ('pathological HIT'). The likelihood of HIT is initially assessed clinically, typically using a scoring system, of which the 4T score is that most utilised. Subsequent laboratory testing to confirm or exclude HIT facilitates exclusion or diagnosis and management. The current investigation comprises a multicentre (n=9) assessment of contemporary laboratory testing for HIT, as performed over the past 1-3 years in each site and comprising testing of over 1200 samples. The primary laboratory test used by study participants (n=8) comprised a chemiluminescence procedure (HIT-IgG(PF4-H)) performed on an AcuStar instrument. Additional immunological testing performed by study sites included lateral flow (STiC, Stago), enzyme linked immunosorbent assay (ELISA), Asserachrom (HPIA IgG), PaGIA (BioRad), plus functional assays, primarily serotonin release assay (SRA) or platelet aggregation methods. The chemiluminescence procedure yielded a highly sensitive screening method for identifying functional HIT, given high area under the curve (AUC, generally ≥0.9) in a receiver operator characteristic (ROC) analysis against SRA as gold standard. ELISA testing resulted in lower ROC AUC scores (<0.8) and higher levels of false positives. Although there is clear association with the likelihood of HIT, the 4T score had less utility than literature suggests, and was comparable to a previous study reported by some of the authors.

A multicenter laboratory assessment of a new automated chemiluminescent assay for ADAMTS13 activity.

BACKGROUND: Thrombotic thrombocytopenic purpura (TTP) is a rare but potentially fatal disorder caused by ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13) deficiency. Prompt identification/exclusion of TTP can thus be facilitated by rapid ADAMTS13 testing. The most commonly utilized (enzyme-linked immunosorbent assay [ELISA]-based) assay takes several hours to perform and so does not generally permit rapid testing. OBJECTIVES: To evaluate the utility of a new automated test for ADAMTS13 activity, the HemosIL AcuStar ADAMTS13 Activity assay, based on chemiluminescence and able to be performed on an ACL AcuStar instrument within 33 minutes. PATIENTS/METHODS: This multicenter (n = 8) assessment included testing of more than 700 test samples, with similar numbers of prospective (n = 348) and retrospective (n = 385) samples. The main comparator was the Technozym ADAMTS13 Activity ELISA. We also assessed comparative performance for detection of ADAMTS13 inhibitors using a Bethesda assay. RESULTS: Overall, the chemiluminescent assay yielded similar results to the comparator ELISA, albeit with slight negative bias. ADAMTS13 inhibitor detection was also comparable, albeit with slight positive bias with the AcuStar assay. Assay precision was similar with both assays, and we also verified assay normal reference ranges. CONCLUSIONS: The HemosIL AcuStar ADAMTS13 Activity assay provided results rapidly, which were largely comparable with the Technozym ADAMTS13 Activity ELISA assay, albeit lower on average. Conversely, inhibitor levels tended to be identified at a higher level on average. Thus, the HemosIL AcuStar ADAMTS13 Activity assay provides a fast and accurate means to quantitate plasma levels of ADAMTS13 for TTP/ADAMTS13 identification/exclusion, and potentially also for other applications.

Anaphylaxis Following Human Prothrombin Complex Concentrate in a Child with Lupus Anticoagulant Hypoprothrombinemia Syndrome: A Cautionary Tale.

A previously healthy 3-year-old girl presented with a short history of mucocutaneous bleeding and a spontaneous left knee hemarthrosis following a nonspecific viral gastroenteritis. Initial investigations for a bleeding disorder revealed a normal platelet count; however, coagulation studies revealed a prothrombin time (PT) of 25 seconds and an activated partial thromboplastin time (APTT) of 66 seconds (both prolonged). The APTT did not correct on mixing with normal plasma, and further testing confirmed the presence of a strong lupus anticoagulant (LA). One-stage assays of factor VIII, VII, and X were normal, but factor II was markedly reduced. Based on this distinct clinicopathological picture, a diagnosis of lupus anticoagulant hypoprothrombinemia syndrome (LAHS) was made. Due to the presence of a hemarthrosis, the patient was treated with clotting factor concentrate. Human prothrombin complex concentrate (PROTHROMBINEX-VF) was used as a source of factor II replacement; however, during the infusion the patient developed anaphylaxis necessitating resuscitation. The patient was observed without further factor replacement, and the bleeding symptoms resolved over several days. Within 3 weeks her PT and factor II had normalized but the APTT remained prolonged. After 6 months the coagulation profile had completely normalized and the LA was negative. It is unusual to require replacement of factor II in paediatric LAHS because bleeding is typically minor and self-limited. Anaphylaxis to clotting factor concentrates has not been previously reported in the context of LAHS, but is well described in patients with congenital factor IX deficiency (hemophilia B). Whilst the potential mechanism for anaphylaxis in our patient is unknown, it is recommended that human prothrombin complex concentrates should be used cautiously in paediatric LAHS.