Thrombophilia Screening: Not So Straightforward.

Although inherited thrombophilias are lifelong risk factors for a first thrombotic episode, progression to thrombosis is multifactorial and not all individuals with inherited thrombophilia develop thrombosis in their lifetimes. Consequently, indiscriminate screening in patients with idiopathic thrombosis is not recommended, since presence of a thrombophilia does not necessarily predict recurrence or influence management, and testing should be selective. It follows that a decision to undertake laboratory detection of thrombophilia should be aligned with a concerted effort to identify any significant abnormalities, because it will inform patient management. Deficiencies of antithrombin and protein C are rare and usually determined using phenotypic assays assessing biological activities, whereas protein S deficiency (also rare) is commonly detected with antigenic assays for the free form of protein S since available activity assays are considered to lack specificity. In each case, no single phenotypic assay is capable of detecting every deficiency, because the various mutations express different molecular characteristics, rendering thrombophilia screening repertoires employing one assay per potential deficiency, of limited effectiveness. Activated protein C resistance (APCR) is more common than discrete deficiencies of antithrombin, protein C, and protein S and also often detected initially with phenotypic assays; however, some centres perform only genetic analysis for factor V Leiden, as this is responsible for most cases of hereditary APCR, accepting that acquired APCR and rare F5 mutations conferring APCR will go undetected if only factor V Leiden is evaluated. All phenotypic assays have interferences and limitations, which must be factored into decisions about if, and when, to test, and be given consideration in the laboratory during assay performance and interpretation. This review looks in detail at performance and limitations of routine phenotypic thrombophilia assays.

Activated Partial Thromboplastin Time and Prothrombin Time Mixing Studies: Current State of the Art.

Mixing studies have long been in the clinical laboratory armamentarium for investigating unexpected, prolonged activated partial thromboplastin time (aPTT) or prothrombin time (PT). The purpose of the mixing study is to identify whether the aPTT/PT prolongation is secondary to a factor deficiency versus an inhibitor, which would present as a "corrected" and "noncorrected" mixing study, respectively. The differentiation between a factor deficiency and inhibitor may likely further direct clinical decisions, including additional diagnostic testing or factor replacement therapy. While aPTT/PT mixing studies are simple tests to perform, there is a lack of standardization for both the testing protocol and the interpretation of what is considered to be a corrected or noncorrected mixing study result. This review will describe the common indications for the mixing test, preanalytic variables that may affect mixing study performance, and describe several methods for interpreting the results of aPTT and PT mixing tests.

Testing for Lupus Anticoagulants.

Lupus anticoagulant (LA) is one of the three criteria antiphospholipid antibodies (aPLs) employed in classification, and by default diagnosis, of antiphospholipid syndrome (APS). Detection of LA is not via calibrated assays but is based on functional behavior of the antibodies in a medley of coagulation assays. A prolonged clotting time in a screening test is followed by demonstration of phospholipid dependence and inhibitory properties in confirmatory and mixing tests, respectively, which are modifications of the parent screening test. Complications arise because no single screening test is sensitive to every LA, and no test is specific for LA, because they are prone to interference by other causes of elevated clotting times. Several screening tests are available but the pairing of dilute Russell's viper venom time (dRVVT) with LA-sensitive activated partial thromboplastin time (aPTT) is widely used and recommended because it is proven to have good detection rates. Nonetheless, judicious use of other assays can improve diagnostic performance, such as dilute prothrombin time to find LA unreactive with dRVVT and aPTT, and the recently validated Taipan snake venom time with ecarin time confirmatory test that are unaffected by vitamin K antagonist and direct factor Xa inhibitor anticoagulation. Expert body guidelines and their updates have improved harmonization of laboratory practices, although some issues continue to attract debate, such as the place of mixing tests in the medley hierarchy, and areas of data manipulation such as assay cut-offs and ratio generation. This article reviews current practices and challenges in the laboratory detection of LA.

Statewide trends and factors associated with genetic testing for hereditary cancer risk in Arkansas 2013-2018.

BACKGROUND: Early identification of hereditary cancer risk would save lives, but genetic testing (GT) has been inadequate. We assessed i) trends for hereditary breast and ovarian cancer (HBOC), Lynch syndrome, and other GT and ii) factors associated with receipt of GT. METHODS: We used data from the Arkansas All-Payer Claims Database from January 2013 through June 2018 (commercial, Medicaid), December 2017 (state employee), or December 2016 (Medicare) and identified enrollees with ≥1 month of enrollment. Using Current Procedural Terminology (CPT-4) codes, rates for GT were calculated per 100,000 person-quarters and time series regressions estimated. Second, GT and covariate information for enrollees with 24 months of continuous enrollment were used to estimate separate logistic regression models for each GT category. RESULTS: Among 2,520,575 unique enrollees, HBOC testing rates were 2.2 (Medicaid), 22.0 (commercial), 40.4 (state employee), and 13.1(Medicare) per 100,000 person-quarters and increased linearly across all plans. Older age (OR=1.24; 95%CI 1.20 - 1.28), female sex (OR=18.91; 95%CI 13.01 - 28.86), higher comorbidity burden (OR=1.08; 95%CI 1.05 - 1.12), mental disorders (OR=1.53; 95%CI 1.15 - 2.00), and state employee coverage (OR=1.65; 95%CI 1.37 - 1.97) were positively associated with HBOC testing. Less than 1 of 10,000 enrollees received Lynch syndrome testing, while < 5 of 10,000 received HBOC testing. CONCLUSION: GT rates for hereditary cancer syndromes have increased in Arkansas but remain low. Receipt of GT was explained with high discrimination by sex and plan type. IMPACT: Expansion of GT for hereditary cancer risk in Arkansas is needed to identify high-risk individuals who could benefit from risk-reduction strategies.

Clinical Validation of an Automated Fluorogenic Factor XIII Activity Assay Based on Isopeptidase Activity.

Hereditary factor XIII (FXIII) deficiency is a rare autosomal bleeding disorder which can cause life-threatening bleeding. Acquired deficiency can be immune-mediated or due to increased consumption or reduced synthesis. The most commonly used screening test is insensitive, and widely used quantitative assays have analytical limitations. The present study sought to validate Technofluor FXIII Activity, the first isopeptidase-based assay available on a routine coagulation analyser, the Ceveron s100. Linearity was evidenced throughout the measuring range, with correlation coefficients of >0.99, and coefficients of variation for repeatability and reproducibility were <5% and <10%, respectively. A normally distributed reference range of 47.0-135.5 IU/dL was derived from 154 normal donors. Clinical samples with Technofluor FXIII Activity results between 0 and 167.0 IU/dL were assayed with Berichrom® FXIII Activity, a functional ammonia release assay, and the HemosIL™ FXIII antigen assay, generating correlations of 0.950 and 0.980, respectively. Experiments with a transglutaminase inhibitor showed that Technofluor FXIII Activity can detect inhibition of enzymatic activity. No interference was exhibited by high levels of haemolysis and lipaemia, and interference by bilirubin was evident at 18 mg/dL, a level commensurate with severe liver disease. Technofluor FXIII Activity is a rapid, accurate and precise assay suitable for routine diagnostic use with fewer interferents than ammonia release FXIII activity assays.

Alternative assays to dRVVT and aPTT for lupus anticoagulant detection.

Lupus anticoagulants (LA) are heterogeneous antibodies and no single assay will detect every LA. Consequently, testing is commonly undertaken with both dilute Russell's viper venom time (dRVVT) and LA-responsive activated partial thromboplastin time (aPTT) to maximize detection rates. Although a huge body of evidence attests to the diagnostic utility of these assays, they have limitations that can render them unreliable in certain circumstances. Other assays are available for detecting LA but unfamiliarity, variable availability and technical concerns expressed in guidelines contribute to less usage than dRVVT and aPTT. However, assays such as Taipan snake venom time and Textarin time are insensitive to anticoagulants that compromise dRVVT and aPTT, and assays such as dilute prothrombin time can detect LA unreactive in dRVVT and aPTT. The pros and cons of alternative assays to dRVVT and APTT for LA detection are discussed.

Mixing studies for lupus anticoagulant: mostly no, sometimes yes.

Mixing tests have long been a mainstay in the lupus anticoagulant (LA) testing armoury of screen, mix and confirm assays. If a sample with an elevated screening test does not evidence inhibition in the mixing test, the search for an LA is halted and a different diagnostic pathway embarked upon. Recent years have seen studies evidencing sometimes high frequencies of false-negative mixing tests with perhaps sinister implications for missed diagnoses and skewed patient management. Issues such as the dilution effect, between-reagent sensitivity and specificity differences, variability of normal pooled plasma (NPP) quality and suitability and interpretive inconsistencies all contribute to questioning the reliability of mixing tests and their pivotal place in the LA assay hierarchy. The advent of integrated testing, where phospholipid-dependence is demonstrated or excluded prior to any attempt to evidence inhibitory properties with a fallible analytical principle, provides an alternative path to LA detection. In the absence of other causes of elevated clotting times, LA assay screen and confirm discordance is sufficient to secure a laboratory diagnosis of the presence of an LA, leaving the mixing test in a supplementary yet valuable role when further diagnostic discrimination is required.

The effect of regional citrate anti-coagulation on the coagulation system in critically ill patients receiving continuous renal replacement therapy for acute kidney injury - an observational cohort study.

BACKGROUND: Regional anticoagulation with citrate is the recommended first line treatment for patients receiving continuous renal replacement therapy (CRRT). There is wide variability in filter patency which may be due to differences in patient characteristics and local practice. It is also possible that citrate has effects on primary and secondary haemostasis, fibrinolysis and platelet function that are still unknown. The primary aim of the study is to describe the effect of citrate on coagulation and fibrinolysis pathways in both the patient and the haemodialysis circuit. METHODS: The study will recruit 12 adult patients admitted to the intensive care unit, requiring CRRT with regional citrate anticoagulation for acute kidney injury. Patients with pre-existing thrombotic or bleeding tendencies will be excluded. Thrombin generation, clot lysis and platelet function will be measured at baseline and at 12, 24, 36, 48 and 72 h after commencing CRRT (from the patient and from the circuit). We will describe the evolution of parameters over time as well as the differences in parameters between the patient and the circuit. DISCUSSION: The study will provide new data on the effects of citrate during continuous renal replacement therapy which is not currently available. We will minimise confounding factors through the use of tight exclusion criteria and accept that this will slow down recruitment. Depending on the results, we hope to incorporate the findings into existing clinical guidelines and clinical practice with the aim to prevent premature filter clotting and interruptions in treatment. TRIAL REGISTRATION: The study was registered with clinicaltrials.gov on 10th June 2015 ( NCT02486614 ).

Platelet-rich plasma for tissue regeneration can be stored at room temperature for at least five days.

BACKGROUND: Autologous platelet-rich plasma (PRP) is gaining increasing use as a wound healing promoter in a variety of clinical settings, including dentistry. Fresh PRP is often used, necessitating daily draws. The present study investigates the possibility of using stored PRP without having to freeze it by storing PRP under variable conditions and assessing growth factor release as a surrogate marker of continued viability. METHODS: Freshly drawn PRP was stored in oxygen permeable and non-oxygen permeable containers under conditions of constant agitation with or without added prostaglandin, intermittent agitation and no agitation, over an 8-day period. Serial platelet counts, mean platelet volume, platelet distribution width and platelet-large cell ratio, and collagen-induced aggregometry were undertaken. Once collagen-induced aggregation had gone to completion, the plasma was centrifuged to pellet platelet material and the supernatants separated and frozen for batched analysis of released platelet-derived growth factor-BB (PDGF-BB). RESULTS: As would be anticipated, platelet counts, percentage aggregation and PDGF-BB levels all reduced over time. Platelet parameters suggested that platelets were more stable in the non-oxygen permeable containers, possibly due to pH drift and a degree of microaggregate formation in the oxygen permeable containers. CONCLUSION: Although platelet integrity and PDGF-BB fell over time, the intermittently agitated non-oxygen permeable container appeared to retain better platelet integrity and function, and PDGF-BB release, than other storage conditions, with potential for clinical use for 5-8 days.

Recent guidelines and recommendations for laboratory detection of lupus anticoagulants.

The International Society on Haemostasis and Thrombosis (ISTH) and the British Committee for Standards in Haematology (BCSH) have recently updated their lupus anticoagulant (LA) detection guidelines. The Clinical and Laboratory Standards Institute (CLSI) subsequently will publish its first LA guideline. General agreement exists on issues such as sample preparation, the use of dilute Russell viper venom time (dRVVT) in diagnostic repertoires, the use of normalized ratios, calculations to demonstrate phospholipid dependence, calculations to demonstrate inhibition, and interpretive reporting. The ISTH recommendation to employ only dRVVT and activated partial thromboplastin time is not mirrored in the BCSH and CLSI documents. The potential for false negatives in mixing tests is acknowledged by all panels, yet they remain mandated by ISTH as there are occasions when they are crucial to diagnostic accuracy. BCSH indicates that a negative mixing test need not exclude the presence of a LA, and CLSI reprioritizes test order to screen-confirm-mix, the latter being considered unnecessary in specific circumstances. Opinions in the guidelines differ on setting cutoff levels (i.e., 97.5th vs. 99th percentile for normally distributed data). All guidelines cover testing of anticoagulated patients, more detail being given by BCSH and CLSI, who suggest that Taipan snake venom time is a useful adjunct test in patients receiving vitamin K antagonists. Although complete agreement is not apparent, the guidelines represent significant moves toward engendering common practices.

Taipan snake venom time has high sensitivity for lupus anticoagulants in non-anticoagulated, triple positive antiphospholipid syndrome patients.

INTRODUCTION: Dilute Russell's viper venom time (dRVVT) and activated partial thromboplastin time (APTT) are the mainstay assays in lupus anticoagulant (LA) detection yet they have limitations, particularly in relation to interferences and specificity. The recently validated Taipan snake venom time (TSVT) screening with ecarin time (ET) confirmatory assays overcome many of those limitations due to the innate specificity engendered from direct prothrombin activation, and insensitivity to the effects of vitamin K antagonists (VKA). The present study aimed to further evidence diagnostic utility of TSVT/ET by performing them in samples from 116 nonanticoagulated patients with established triple-positive antiphospholipid syndrome (APS). METHODS: Samples were identified in three expert centres who performed dRVVT, APTT and solid phase antiphospholipid antibody assays with reagents from a variety of manufacturers. All samples additionally received TSVT/ET analysis using standardised reagents. RESULTS: Ninety seven of 116 (83.6%) were dRVVT- and APTT-positive, 85/97 (87.6%) of which were TSVT/ET-positive, 9/116 (7.8%) were dRVVT-positive only, 6 of which were TSVT/ET-positive, and 10/116 (8.6%) were APTT-positive only, 5 of which were TSVT/ET-positive. 96/116 TSVT/ET-positivity returned a high sensitivity for LA of 82.8%. Low coefficients of determination revealed weak relationships between LA potency and anticardiolipin and anti-ß2-glycoprotein I antibody titres for all three LA assays. CONCLUSIONS: TSVT/ET has high sensitivity for the clinically significant LA found in triple positive APS patients. TSVT/ET can establish multiple LA assay positivity in nonanticoagulated patients negative for one of dRVVT or APTT, and is the only assay pairing insensitive to VKAs, the recommended anticoagulation for APS.

Toward harmonized interpretation of anticardiolipin and anti-ß2-glycoprotein I antibody detection for diagnosis of antiphospholipid syndrome using defined level intervals and likelihood ratios: communication from the ISTH SSC Subcommittee on Lupus Anticoagulant/Antiphospholipid Antibodies.

BACKGROUND: Improving harmonization of the clinical interpretation of anticardiolipin (aCL) and anti-ß2-glycoprotein I (aß2GPI) antibodies immunoglobulin G (IgG)/immunoglobulin M (IgM) in the diagnosis of antiphospholipid syndrome (APS) is desirable. Likelihood ratios (LRs) with corresponding test-result intervals can identify the power of a test to discriminate between a diseased and nondiseased patient and may be useful for the semiquantitative interpretation of aCL/aß2GPI results. OBJECTIVES: To determine moderate and high thresholds for aCL and aß2GPI IgG/IgM measured with chemiluminescent immunoassay, enzyme-linked immunosorbent assay, fluorescence enzyme immunoassay, and multiplex flow immunoassay. METHODS: aCL and aß2GPI antibodies IgG/IgM were determined with 4 solid-phase systems in a case-control study population including 381 APS patients and 727 controls. Interval-specific LRs (IS-LR) were calculated for ranges determined by prespecified specificity and sensitivity levels. Three methods were used for determining thresholds that separated low, moderate, and high positive antibody levels. Interassay agreement was checked with Cohen's kappa statistics. RESULTS: Assay- and antibody-specific thresholds demonstrated increasing IS-LR, reflecting different clinical significance for low, moderate, and high levels, especially for IgG aCL and aß2GPI and in thrombotic APS. IS-LRs per antibody and unit range were comparable across solid-phase platforms resulting in enhanced harmonization of result interpretation. Agreement between assays for identifying high levels was improved by semiquantitative interpretation compared with that by quantitative reporting. CONCLUSION: aCL and aß2GPI IgG/IgM moderate and high thresholds were determined for 4 analytical platforms. Thresholds improve harmonized interpretation of aCL/aß2GPI levels across platforms. The proposed thresholds should be verified in an independent case-control study to check interlaboratory transferability.

Lupus Anticoagulant Testing: Taipan Snake Venom Time with Ecarin Time as Confirmatory Test.

Testing for lupus anticoagulants (LA) in the presence of therapeutic anticoagulation is largely discouraged because of the risk of false-positive and false-negative results, although the ability to detect LA in this setting can be clinically valuable. Strategies such as mixing tests and anticoagulant neutralization can be effective, but have their own limitations. The prothrombin activators in venoms from Coastal Taipan and Indian saw-scaled viper snakes provide an additional analytical avenue in that they are insensitive to the effects of vitamin K antagonists and inevitably bypass the effects of direct factor Xa inhibitors. Oscutarin C in Coastal Taipan venom is phospholipid- and Ca2+-dependent, so the venom is used in a dilute phospholipid design as an LA screening test called the Taipan snake venom time (TSVT). The ecarin fraction of Indian saw-scaled viper venom is cofactor-independent and operates as a prothrombin-activated confirmatory test, the ecarin time, because the absent phospholipid precludes inhibition by LAs. Bypassing all coagulation factors except prothrombin and fibrinogen renders the assays innately more specific than other LA assays, while TSVT as a screening test has good sensitivity to LAs detected in other assays, as well as occasional antibodies unreactive in other assays.

Lupus Anticoagulant Testing: Dilute Prothrombin Time (dPT).

Lupus anticoagulants (LA) rarely affect routine prothrombin time assays because the high phospholipid (PL) content in thromboplastin reagents tends to overwhelm the antibodies. Dilution of thromboplastin to create a dilute prothrombin time (dPT) screening test renders the assay sensitive to the presence of LA. Technical and diagnostic performances are enhanced if recombinant thromboplastins are employed in place of tissue-derived reagents. Presence of an LA cannot be deduced from an elevated screening test alone since other coagulation disturbances can prolong clotting times. Confirmatory testing with less dilute or undiluted thromboplastin reveals the PL-dependent nature of LA by reducing the clotting time relative to that of the screening test. Where appropriate, such as a known or suspected coagulation factor deficiency, mixing tests are valuable in correcting factor deficiencies and evidencing inhibitory properties of LA, to increase diagnostic specificity. Although LA testing is commonly restricted to dilute Russell's viper venom time and activated partial thromboplastin time, dPT is sensitive to LA unreactive in those assays, and inclusion in routine testing increases detection rates of clinically significant 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.

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.

Factor V Leiden-independent activated protein C resistance: Communication from the plasma coagulation inhibitors subcommittee of the International Society on Thrombosis and Haemostasis Scientific and Standardisation Committee.

Activated protein C resistance (APC-R) due to the single-nucleotide polymorphism factor V Leiden (FVL) is the most common cause of hereditary thrombophilia. It is found predominantly in Caucasians and is uncommon or absent in other populations. Although FVL is responsible for >90% of cases of hereditary APC-R, a number of other F5 variants that also confer various degrees of APC-R and thrombotic risk have been described. Acquired APC-R due to increased levels of coagulation factors, reduced levels of inhibitors, or the presence of autoantibodies occurs in a variety of conditions and is an independent risk factor for thrombosis. It is common for thrombophilia screening protocols to restrict assessment for APC-R to demonstrating the presence or absence of FVL. The aim of this Scientific and Standardisation Committee communication is to detail the causes of FVL-independent APC-R to widen the diagnostic net, particularly in situations in which in vitro APC-R is encountered in the absence of FVL. Predilution clotting assays are not FVL specific and are used to detect clinically significant F5 variants conferring APC-R, whereas different forms of acquired APC-R are preferentially detected using the classical activated partial thromboplastin time-based APC-R assay without predilution and/or endogenous thrombin potential APC-R assays. Resource-specific recommendations are given to guide the detection of FVL-independent APC-R.

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.

Triple-positive antiphospholipid syndrome does not guarantee positivity in each lupus anticoagulant assay.

BACKGROUND: Triple positivity for all 3 criteria antiphospholipid antibodies confers high risk of symptom development in carriers, and recurrence in antiphospholipid syndrome (APS). Most triple-positivity studies report lupus anticoagulant (LA) testing as positive without distinguishing between positivity with dilute Russell's viper venom time (dRVVT) and activated partial thromboplastin time (APTT) and single-assay positivity or only perform dRVVT. Single LA assay repertoires remain in use in some centers, which risks missing some triple positives. Positivity with both assays may identify higher risk. OBJECTIVES: The aim of this study is to investigate the frequency of single LA assay positivity in triple-positive patients. METHODS: Three hundred forty-two triple-positive profiles from nonanticoagulated patients (237 APS, 45 systemic lupus erythematosus without APS symptoms, and 60 nonclinical criteria) were identified from laboratory databases and assessed for LA positivity by dRVVT and/or APTT. RESULTS: Seventy-three of 237 (30.8%) APS samples were LA-positive with 1 assay, 40/237 (16.9%) by dRVVT only, and 33/237 (13.9%) with APTT only. Nineteen of 45 (42.2%) were LA-positive with 1 assay in the systemic lupus erythematosus cohort; 12/45 (26.7%) with dRVVT only and 7/45 (15.5%) with APTT only. Thirty-three of 60 (55.0%) were LA-positive with 1 assay in the nonclinical criteria cohort; 24/60 (40.0%) with dRVVT only and 9/60 (15.0%) with APTT only. The most common solid-phase assay profile was elevated immunoglobulin G aCL and aß2GPI. CONCLUSION: Up to 55.0% of triple-positive samples were positive in 1 LA assay, representing significant potential for misdiagnosis and inappropriate management via single LA assay repertoires.