Performance of Chromogenic Protein C (PC) Testing.

Protein C (PC) is a vitamin K-dependent zymogen synthesized in the liver that plays a major role in regulating the coagulation pathway. Upon interaction with the thrombin-thrombomodulin complex, PC is converted to its active form, activated PC (APC). APC complexes with protein S and regulates thrombin generation by the inactivation of Factors Va and VIIIa. The role of PC as a key regulator of the coagulation process is highlighted in the deficiency state, in which heterozygous deficiency of PC predisposes to an increased risk of venous thromboembolism (VTE), while in the homozygous deficiency state, potentially fatal complications in the fetus including purpura fulminans and disseminated intravascular coagulation (DIC) can occur. Protein C is often measured with other factors such as protein S and antithrombin as a screen in the investigation of VTE. The chromogenic PC assay, the protocol described in this chapter, quantitates the amount of functional PC in the plasma using an activator of PC with the degree of color change proportional to the amount of PC present in the sample. Other methods, including functional clotting-based assays and antigenic assays, are available; however, protocols for these assays will not be provided in this chapter.

International Council for Standardization in Haematology (ICSH) laboratory guidance for the verification of haemostasis analyser-reagent test systems. Part 2: Specialist tests and calibrated assays.

Before a new method is used for clinical testing, it is essential that it is evaluated for suitability for its intended purpose. This document gives guidance for the performance, verification and implementation processes required by regulatory and accreditation bodies. It covers the planning and verification of specialist haemostatic tests, including factor assays, D-dimers, direct anticoagulants and thrombophilia testing.

International Council for Standardization in Haematology (ICSH) laboratory guidance for the evaluation of haemostasis analyser-reagent test systems. Part 1: Instrument-specific issues and commonly used coagulation screening tests.

Before a new method is used for clinical testing, it is essential that it is evaluated for suitability for its intended purpose. This document gives guidance for the performance of verification, validation and implementation processes required by regulatory and accreditation bodies. It covers the planning and execution of an evaluation of the commonly performed screening tests (prothrombin time, activated partial thromboplastin time, thrombin time and fibrinogen assay), and instrument-specific issues. Advice on selecting an appropriate haemostasis analyser, planning the evaluation, and assessing the reference, interval, precision, accuracy, and comparability of a haemostasis test system are also given. A second companion document will cover specialist haemostasis testing.

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.

Factor V inhibitors: rare or not so uncommon? A multi-laboratory investigation.

Acquired deficiencies of, or inhibitors to, factor V are considered rare events. We report a series of 14 acquired factor V deficiencies, 10 of which were confirmed to have inhibitors to factor V, as identified within Australia in the past 5 years following a multi-laboratory investigation. The initial index case seen by one laboratory was followed within 4 months by a separate similar case. This prompted local contact with colleagues (n = 20) working in other haemostasis referral laboratories to identify the current case series. In total, nearly one-half of all haemostasis referral laboratories contacted had seen a case within the past 5 years. Clinical features and the apparent associated risk of bleeding complications generally varied, as did laboratory findings and the likely causal event. There were three females and 11 males. Age ranged from 44 to 95 years (median, 81 years). The level of inhibitor ranged from undetectable to over 250 Bethesda units. The probable cause leading to development of the inhibitors ranged from exposure to bovine thrombin, exposure to antibiotics, surgery and malignancy. Of additional interest was the apparent association of anti-phospholipid antibodies in many of the cases. For example, in the two similar index cases, with factor V inhibitor titres > 200 Bethesda units, high levels of anti-cardiolipin antibodies (> 70 GPL units) were also detected. Although less clear because of inhibitor interference, many of the cases also showed evident co-associated lupus anticoagulant activity. In conclusion, we report a series of factor V inhibitors recently identified within our geographic region that would represent an annual incidence of around 0.29 cases per million Australians. Although considered a rare finding, there is a high likelihood that most haemostasis referral laboratories will see a case every five or so years.

Systematic application of multiplex PCR enhances the detection of bacteria, parasites, and viruses in stool samples.

OBJECTIVES: To determine whether systematic testing of faecal samples with a broad range multiplex PCR increases the diagnostic yield in patients with diarrhoea compared with conventional methods and a clinician initiated testing strategy. METHODS: 1758 faecal samples from 1516 patients with diarrhoea submitted to two diagnostic laboratories were tested for viral, bacterial, and parasitic pathogens by Fast-Track Diagnostics multiplex real-time PCR kits and conventional diagnostic tests. RESULTS: Multiplex PCR detected pathogens in 530 samples (30%): adenovirus (51, 3%), astrovirus (95, 5%), norovirus (172, 10%), rotavirus (3, 0.2%), Campylobacter jejuni/coli (85, 5%), Salmonella spp. (22, 1%), Clostridium difficile (72, 4%), entero-haemorrhagic Escherichia coli (21, 1%), Cryptosporidium spp. (3, 0.2%), Entamoeba histolytica (1, 0.1%), and Giardia lamblia (59, 3%). In contrast, conventional testing detected a pathogen in 324 (18%) samples. CONCLUSIONS: Using a systematic approach to the diagnosis of gastroenteritis improved diagnostic yield. This enhanced detection with PCR was achieved by a combination of improved detection of individual pathogens and detection of pathogens not requested or unable to be tested by conventional tests. This approach also allowed earlier identification for most pathogens and created a workflow which is likely to adapt well for many diagnostic laboratories.