Use of the ADAMTS13 activity assay improved the accuracy and efficiency of the diagnosis and treatment of suspected acquired thrombotic thrombocytopenic purpura

Laboratory investigation and diagnosis of thrombotic thrombocytopenic purpura

Thrombotic thrombocytopenic purpura (TTP) is a rare and potentially fatal disease for which rapid diagnosis is crucial for patient outcomes. Deficient activity (< 10%) of the liver enzyme, ADAMTS13, is the pathophysiological hallmark of TTP, and measurement of the enzyme activity can establish the diagnosis of TTP with high accuracy. Thus, along with the clinical history, appropriate laboratory assessment of a suspected case of TTP is essential for diagnosis and treatment. Here, we present a review of the available laboratory tests that can assist clinicians in establishing the diagnosis of TTP, with special focus on ADAMTS13 assays, including the measurement of the antigen and activity, and detection of autoantibodies to ADAMTS13.

ADAMTS13 Activity Measurement by ELISA and Fluorescence Resonance Energy Transfer Assay

Accurate estimation of ADAMTS13 (a disintegrin-like and metalloprotease with thrombospondin type 1 motif, member 13) activity level is crucial in the diagnostic setting of differentiation between thrombotic thrombocytopenic purpura (TTP) and other thrombotic microangiopathies. The original assays were too cumbersome and time-consuming for use in the acute situation, and treatment was often based on clinical findings alone, with confirmatory laboratory assays following days or weeks later. Rapid assays are now available that can generate results fast enough to impact on immediate diagnosis and management. Assays based on fluorescence resonance energy transfer (FRET) or chemiluminescence principles can generate results in less than an hour, although they require specific analytical platforms. Enzyme-linked immunosorbent assays (ELISA) can generate results in about 4 h, but do not require specialized equipment beyond ELISA plate readers that are in regular use in many laboratories. The present chapter describes principles, performance, and practical aspects of an ELISA and a FRET assay, for quantitative measurement of ADAMTS13 activity in plasma.

ADAMTS13 Antibody and Inhibitor Assays

A finding of an ADAMTS13 (a disintegrin-like and metalloprotease with thrombospondin type 1 motif, member 13) activity level of <10% of normal is usually sufficient to distinguish thrombotic thrombocytopenic purpura (TTP) from other thrombotic microangiopathies. TTP can be congenital or acquired, the most common form being acquired immune-mediated TTP caused by autoantibodies than inhibit ADAMTS13 function and/or increase its clearance. Basic 1 + 1 mixing tests can detect the presence of inhibitory antibodies, and quantification can be achieved with Bethesda-type assays that measure loss of function in a series of mixtures of test plasma and normal plasma. Not all patients present with inhibitory antibodies, and here the ADAMTS13 deficiency may be caused by clearing antibodies alone, which are not detectable in functional assays. ELISA assays are commonly used to detect clearing antibodies via capture with recombinant ADAMTS13. Since they also detect inhibitory antibodies, they are the preferred assay, although they cannot distinguish between inhibitory and clearing antibodies. The present chapter describes principles, performance, and practical aspects of a commercial ADAMTS13 antibody ELISA and a generic approach to Bethesda-type assays for detecting inhibitory ADAMTS13 antibodies.

ADAMTS13 Activity: Screening Test Protocol

Accurate estimation of ADAMTS13 (a disintegrin-like and metalloprotease with thrombospondin type 1 motif, member 13) activity level is necessary for diagnosis and management of thrombotic microangiopathies (TMA). In particular, it permits distinction between thrombotic thrombocytopenic purpura (TTP) and other TMAs, prompting disorder appropriate treatment. Manual and automated quantitative assays of ADAMTS13 activity are commercially available, some providing results within less than an hour, but they require specialist equipment and personnel and tend to only be available in specialized diagnostic facilities. Technoscreen ADAMTS13 Activity is a rapid, commercially available, semiquantitative screening test employing flow-through technology and an ELISA activity assay principle. It is a simple to perform screening tool, not requiring specialist equipment or personnel. The colored end point is compared to a reference color chart containing four color intensity indicators corresponding to ADAMTS13 activity levels of 0, 0.1, 0.4, or 0.8 IU/mL. Reduced levels detected in the screening test should be confirmed by quantitative assay. The assay lends itself to use in nonspecialized laboratories, remote, and point-of-care settings.

The perfect storm: Thrombotic thrombocytopenic purpura (TTP) associated with COVID-19, a clinical case series and review

This is a case series of three patients in our hospital system who developed acquired thrombotic thrombocytopenic purpura (aTTP) after testing positive for COVID-19 infection. Two patients had acute COVID-19 infections, and one had COVID-19 IgG antibodies consistent with prior COVID-19 infection. Twelve additional cases of aTTP after COVID-19 infection were found in the literature. COVID-19 creates alterations in the vWF-ADAMTS-13 axis with reduced ADAMTS-13 in acute illness that may lead those patients who are predisposed into fulminant aTTP. Further genetic studies are necessary to uncover why some patients with COVID-19 can have concurrent aTTP. For those with a prior COVID-19 infection, molecular mimicry with autoantibodies to ADAMTS-13 is likely the predominant trigger, but having an underlying predisposition (prior episode of TTP, genetic predisposition to autoimmune conditions, or breast cancer history) creates an environment that could be a possible trigger for aTTP.

Translation of a Protease Turnover Assay for Clinical Discrimination of Mucinous Pancreatic Cysts

The classification of pancreatic cyst fluids can provide a basis for the early detection of pancreatic cancer while eliminating unnecessary procedures. A candidate biomarker, gastricsin (pepsin C), was found to be present in potentially malignant mucinous pancreatic cyst fluids. A gastricsin activity assay using a magnetic bead-based platform has been developed using immobilized peptide substrates selective for gastricsin bearing a dimeric rhodamine dye. The unique dye structure allows quantitation of enzyme-cleaved product by both fluorescence and surface enhanced Raman spectroscopy (SERS). The performance of this assay was compared with ELISA assays of pepsinogen C and the standard of care, carcinoembryonic antigen (CEA), in the same clinical sample cohort. A retrospective cohort of mucinous (n = 40) and non-mucinous (n = 29) classes of pancreatic cyst fluid samples were analyzed using the new protease activity assay. For both assay detection modes, successful differentiation of mucinous and non-mucinous cyst fluid was achieved using 1 µL clinical samples. The activity-based assays in combination with CEA exhibit optimal sensitivity and specificity of 87% and 93%, respectively. The use of this gastricsin activity assay requires a minimal volume of clinical specimen, offers a rapid assay time, and shows improvements in the differentiation of mucinous and non-mucinous cysts using an accurate standardized readout of product formation, all without interfering with the clinical standard of care.

Microangiopathic Haemolytic Anaemia in a Young Male Patient With Oesophageal Carcinoma

Microangiopathic haemolytic anaemia (MAHA) in patients with various solid cancers and haematological malignancies has been reported, but to our knowledge, there has been no clearly reported case of MAHA in a young patient with oesophageal adenocarcinoma. MAHA is a subgroup of haemolytic anaemias characterised by destruction of red blood cells as they traverse small-calibre blood vessels. Its most defining features are anaemia and presence of fragmented red blood cells in the circulation. MAHA associated with cancer is now a well-recognized paraneoplastic syndrome, seen in various solid tumours and haematological malignancies, the most common being gastric, breast and lung carcinoma. The development of MAHA associated with any malignant process is usually an ominous condition, not only because of the fact that no convincing treatment has been discovered to date, but also because it invariably almost always occurs in disseminated cancers as a late presentation.

The prompt identification of the signs and symptoms suggestive of intravascular haemolysis, the deliberation of the cause of such symptoms and the concurrent ruling out of related conditions which may mimic MAHA symptoms such as haemolytic uremic syndrome and thrombotic thrombocytopenic purpura are crucial to ensure successful treatment. The patient is a 33-year-old male patient of Asian descent who had oesophageal adenocarcinoma that had metastasized to the peritoneal cavity and para-aortic lymph nodes. The patient was admitted with bilateral extensive deep vein thrombosis, and was later found to have pulmonary embolism as well. A few days after his admission, he suddenly developed shortness of breath, severe chest pain and was diagnosed with cancer-associated MAHA. His sudden, rapid clinical deterioration, and the inability to intervene successfully was a traumatizing experience for his doctors and relatives alike.

Evaluation and Management of Thrombotic Thrombocytopenic Purpura in the Emergency Department

BACKGROUND

Thrombotic thrombocytopenic purpura (TTP) is a dangerous condition that can be misdiagnosed in the emergency department.

OBJECTIVE

The purpose of this narrative review article is to provide a summary of the background, pathophysiology, diagnosis, and management of TTP, with a focus on emergency clinicians.

DISCUSSION

TTP is a disorder with microangiopathic hemolytic anemia, severe thrombocytopenia, and multiorgan ischemic injury. It may be acquired or hereditary, and is caused by a reduced amount or function of a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13 (ADAMTS13), which is an enzyme involved in cleaving von Willebrand factor. The classic presentation of TTP includes fever, neurologic abnormalities, thrombocytopenia with purpura, microangiopathic hemolytic anemia, and acute renal injury. However, < 7% of cases have all of these findings present. Testing should include a complete blood count, complete metabolic panel, blood smear, coagulation panel, fibrinogen, D-dimer, lactate dehydrogenase, ADAMTS13 level, troponin, human immunodeficiency virus assessment, urinalysis, pregnancy test as appropriate, and electrocardiogram. Management includes hematology consultation if available, plasma exchange and corticosteroids, and treatment of end-organ complications. All patients require admission for treatment and close monitoring.

CONCLUSION

TTP is a potentially dangerous medical condition requiring rapid diagnosis and management. It is essential for emergency clinicians to know how to diagnose and treat this disorder.

Immature platelet dynamics correlate with ADAMTS13 deficiency and predict therapy response in immune-mediated thrombotic thrombocytopenic purpura

INTRODUCTION

Thrombotic thrombocytopenic purpura (TTP) requires prompt initiation of therapeutic plasma exchange (TPE) to avoid significant morbidity and mortality. ADAMTS13 activity testing defines TTP, however, at most institutions this is a send-out test and therapy is often initiated prior to measurement availability. We describe our experience looking at absolute immature platelet counts (A-IPC) in patients suspected with TTP at presentation and in response to therapy.

MATERIALS AND METHODS

Forty-eight patients treated for suspected TTP with A-IPC measure on admission and during hospitalization met inclusion criteria. Of these patients, sixteen had new-onset TTP (ADAMTS13 < 10%), ten were relapsing patients (first diagnosis prior to study period), and 22 were classified as non-TTP (ADAMTS13 ≥ 10%).

RESULTS

Patients with ADAMTS13 deficiency (TTP) had A-IPC different from those without deficiency. A-IPC of 1-2 × 10⁹/L at presentation had high sensitivity and specificity with a negative predictive value of 95.5 to 100%. Two-to-three-fold increases in A-IPC from count prior to TPE initiation was limited to ADAMTS13 deficient patients who was the group responding to therapy. Increases were higher in patients with new disease onset compared to relapsing patients (p = 0.018). Likewise, relapsing patients' A-IPC appeared dependent upon platelet count at time of relapse. A-IPC predicted and correlated with ADAMTS13 deficiency in new-onset TTP (p = 0.0002).

CONCLUSIONS

Only patients with A-IPC-fold increases responded to TPE with platelet count normalization. Our results represent a proof of concept that A-IPC measurements can supplement ADAMTS13 testing and determine response to TPE. Future studies are needed to establish ways to apply these findings in the setting of suspected TTP.

A multi-center evaluation of TECHNOSCREEN® ADAMTS-13 activity assay as a screening tool for detecting deficiency of ADAMTS-13

BACKGROUND

Quantifying A disintegrin-like and metalloprotease with thrombospondin type 1 motif, member 13 (ADAMTS-13) activity enhances thrombotic thrombocytopenic purpura (TTP) diagnosis but most assays are time consuming, technically demanding, and mainly available in reference centers.

OBJECTIVE

Evaluate a simple, semiquantitative ADAMTS-13 activity screening test for early identification/exclusion of TTP.

PATIENTS/METHODS

Plasma from 220 patients with suspected thrombotic microangiopathy at three reference centers were tested with TECHNOSCREEN® ADAMTS13 activity screening test in comparison with TECHNOZYM® ADAMTS-13 activity ELISA at two centers, and in-house fluorescence resonance energy transfer assay at the third center. The screening test indicates if ADAMTS-13 activity is at one of four level-indicator points: 0, 0.1, 0.4, or 0.8 IU/mL.

RESULTS

Screen results were interpreted as binary data in that ADAMTS-13 activity was above or below the 0.1 IU/mL TTP clinical threshold. Combining all sites' data, the screen exhibited 88.7% sensitivity, 90.4% specificity, 74.6% positive predictive value, and 96.2% negative predictive value, comparable to published data for quantitative assays. Five samples with quantitative results below the threshold gave screen readings of 0.1 IU/mL and seven marginally above the threshold gave screen readings of zero. All would warrant plasma exchange while the level is quantified. Nine samples with normal/near normal results gave screens of zero and confirmatory quantifications would prompt early treatment withdrawal, as is current practice. One sample generated screen/quantitative results of 0.4/0.00 IU/mL respectively and was the only clear false-negative.

CONCLUSIONS

The screening test provides more rapid ADAMTS-13 level evaluation than most currently available assays. Its simple operation renders it suitable for adoption in routine or specialist laboratory environments.

Potential impact of a delayed ADAMTS13 result in the treatment of thrombotic microangiopathy: an economic analysis

BACKGROUND

A pre-plasma exchange ADAMTS13 measurement differentiates thrombotic thrombocytopenic purpura (TTP) from other forms of thrombotic microangiopathy (TMA). Given that many hospitals do not perform the ADAMTS13 assay in-house and that the turnaround time (TAT) differs among reference laboratories, we performed an analysis investigating the potential impact of a delay in obtaining the results on the healthcare system.

METHODS

An economic model was developed to estimate the impact of a delay in obtaining the pretreatment ADAMTS13 results on patients admitted with TMA with cost (US dollars) as the primary outcome. Incremental cost-effectiveness ratio (ICER) as a composite outcome was calculated from both cost and life days [LDs], an effectiveness surrogate marker. Model parameters were gathered from the medical literature, except for the institutional cost of the ADAMTS13 test.

RESULTS

In patients with TMA, during the 6-day study period, the incremental cost to the healthcare system ranged from approximately $4155 to $5123 for every 1-day delay in obtaining the pre-exchange ADAMTS13 results with virtually no change in the effectiveness marker. The ICER composite outcome established the cost-effectiveness of having a fast TAT for pre-exchange ADAMTS13 results. Probabilistic sensitivity analyses also confirmed the robustness of the model.

CONCLUSIONS

In patients with clinical presentations of TMAs, having a rapid TAT for pre-exchange ADAMTS13 measurement appeared to be cost-effective. If testing cannot be performed in-house, then our findings support the necessity of contracting with a reference laboratory that can reliably provide the result, preferably within 1 day of admission.

Clinical Features and Gene Mutation Analysis of Congenital Thrombotic Thrombocytopenic Purpura in Neonates

Congenital thrombotic thrombocytopenic purpura (TTP) is a rare hereditary disease with a high mortality rate; however, improved patient survival is possible with prompt diagnosis and treatment. The clinical features and mutation sites of a disintegrin and metalloproteinase with thrombospondin motifs 13 (ADAMTS13) in congenital TTP were analyzed in a neonate with suspected congenital TTP. High-throughput sequencing, polymerase chain reaction, and Sanger sequencing were utilized for screening of genes related to thrombocytopenic diseases and ADAMTS13 gene mutation testing on blood samples from the neonate and the parents. Domestic and foreign literature reporting the clinical features and variants of ADAMTS13 in neonates with congenital TTP were retrieved, compared, and analyzed. The patient in this case was a girl who had been born for 1 h and admitted to the hospital due to "dyspnea for 1 h." Routine blood tests on admission revealed profound thrombocytopenia. She quickly developed symptoms of systemic hemorrhage and eventually died. The neonate had two older sisters who had died of idiopathic thrombocytopenia and hemorrhage within 24 h of birth. Genetic testing showed that the neonate harbored a compound heterozygous mutation in ADAMTS13, c.1187G>A/c.1595G>T, which is a novel variant. Of the 12 cases (1 case in China and 11 cases in other countries) of congenital TTP in neonates that have been reported globally, ADAMTS13 mutation analysis was only performed in eight neonates. Common clinical manifestations included dyspnea of unknown etiology, bruising, jaundice, hemorrhage, and thrombocytopenia. Hence, the current case contributes to our understanding of the clinical manifestations and types of variants in neonates with congenital TTP. Our results demonstrate the efficacy of high-throughput sequencing technology in genetic testing of neonates suspected with congenital TTP and have revealed a novel compound missense mutation in ADAMTS13 that has not been reported in China or elsewhere.

Thrombotic Thrombocytopenic Purpura Following Aortic Valve Replacement with St. Jude Medical Trifecta Bio-Prosthesis

Thrombocytopenia is a recognized complication following aortic valve replacement (AVR). While post-operative thrombotic thrombocytopenic purpura (TTP) is less common than heparin-induced thrombocytopenia (HIT), it is associated with high mortality and morbidity and prompt diagnosis and treatment is vital. In this case report, we describe the first reported case of TTP after AVR using the trifecta bio-prosthesis. We recommend that patients with severe and progressive thrombocytopenia following biological AVR should have early screening for both HIT and TTP, to shorten the decision-making process and provide the appropriate therapy.

Thrombotic thrombocytopenic purpura: pathogenesis, diagnosis and potential novel therapeutics

Thrombotic thrombocytopenic purpura (TTP), a potentially fatal clinical syndrome, is primarily caused by autoantibodies against the von Willebrand factor (VWF)-cleaving metalloprotease ADAMTS-13. In general, severe deficiency of plasma ADAMTS-13 activity (< 10 IU dL-1 ) with or without detectable inhibitory autoantibodies against ADAMTS-13 supports the diagnosis of TTP. A patient usually presents with thrombocytopenia and microangiopathic hemolytic anemia (i.e. schistocytes, elevated serum lactate dehydrogenase, decreased hemoglobin and haptoglobin) without other known etiologies that cause thrombotic microangiopathy (TMA). Normal to moderately reduced plasma ADAMTS-13 activity (> 10 IU dL-1 ) in a similar clinical context supports an alternative diagnosis such as atypical hemolytic uremic syndrome (aHUS) or other types of TMA. Prompt differentiation of TTP from other causes of TMA is crucial for the initiation of an appropriate therapy to reduce morbidity and mortality. Although plasma infusion is often sufficient for prophylaxis or treatment of hereditary TTP due to ADAMTS-13 mutations, daily therapeutic plasma exchange remains the initial treatment of choice for acquired TTP with demonstrable autoantibodies. Immunomodulatory therapies, including corticosteroids, rituximab, vincristine, cyclosporine, cyclophosphamide and splenectomy, etc., should be considered to eliminate autoantibodies for a sustained remission. Other emerging therapeutic modalities, including recombinant ADAMTS-13, adeno-associated virus (AAV) 8-mediated gene therapy, platelet-delivered ADAMTS-13, and antagonists targeting the interaction between platelet glycoprotein 1b and VWF are under investigation. This review highlights the recent progress in our understanding of the pathogenesis and diagnosis of, and current and potential novel therapies for, hereditary and acquired TTP.

ADAMTS13 test and/or PLASMIC clinical score in management of acquired thrombotic thrombocytopenic purpura: a cost-effective analysis

BACKGROUND

The ADAMTS13 test distinguishes thrombotic thrombocytopenic purpura (TTP) from other thrombotic microangiopathies (TMAs). The PLASMIC score helps determine the pretest probability of ADAMTS13 deficiency. Due to inherent limitations of both tests, and potential adverse effects and cost of unnecessary treatments, we performed a cost-effectiveness analysis (CEA) investigating the benefits of incorporating an in-hospital ADAMTS13 test and/or PLASMIC score into our clinical practice.

STUDY DESIGN AND METHODS

A CEA model was created to compare four scenarios for patients with TMAs, utilizing either an in-house or a send-out ADAMTS13 assay with or without prior risk stratification using PLASMIC scoring. Model variables, including probabilities and costs, were gathered from the medical literature, except for the ADAMTS13 send-out and in-house tests, which were obtained from our institutional data.

RESULTS

If only the cost is considered, in-house ADAMTS13 test for patients with intermediate- to high-risk PLASMIC score is the least expensive option ($4,732/patient). If effectiveness is assessed as measured by the number of averted deaths, send-out ADAMTS13 test is the most effective. Considering the cost/effectiveness ratio, the in-house ADAMTS13 test in patients with intermediate- to high-risk PLASMIC score is the best option, followed by the in-house ADAMTS13 test without the PLASMIC score.

CONCLUSIONS

In patients with clinical presentations of TMAs, having an in-hospital ADAMTS13 test to promptly establish the diagnosis of TTP appears to be cost-effective. Utilizing the PLASMIC score further increases the cost-effectiveness of the in-house ADAMTS13 test. Our findings indicate the benefit of having a rapid and reliable in-house ADAMTS13 test, especially in the tertiary medical center.

ADAMTS13 and von Willebrand factor in thrombotic thrombocytopenic purpura

Pathogenesis of thrombotic thrombocytopenic purpura (TTP) was a mystery for over half a century until the discovery of ADAMTS13. ADAMTS13 is primarily synthesized in the liver, and its main function is to cleave von Willebrand factor (VWF) anchored on the endothelial surface, in circulation, and at the sites of vascular injury. Deficiency of plasma ADAMTS13 activity (<10%) resulting from mutations of the ADAMTS13 gene or autoantibodies against ADAMTS13 causes hereditary or acquired (idiopathic) TTP. ADAMTS13 activity is usually normal or modestly reduced (>20%) in other forms of thrombotic microangiopathy secondary to hematopoietic progenitor cell transplantation, infection, and disseminated malignancy or in hemolytic uremic syndrome. Plasma infusion or exchange remains the initial treatment of choice to date, but novel therapeutics such as recombinant ADAMTS13 and gene therapy are under development. Moreover, ADAMTS13 deficiency has been shown to be a risk factor for the development of myocardial infarction, stroke, cerebral malaria, and preeclampsia.