Index Of Circulating Anticoagulant Research Articles

Difference in activated partial thromboplastin time values with two different reagents according to C-reactive protein values.

Activated partial thromboplastin time (APTT) is susceptible to reagent composition. This study aimed to investigate a large number of specimens and determine the cause of discrepancies. This study included 18,994 subjects who underwent coagulation tests at our hospital from May 2020 to December 2020. Measuring reagents included HemosIL SynthASil APTT (APTT-SS, Instrumentation Laboratory) and Coagpia APTT-N (APTT-N, Sekisui Medical). A total of 451 patients demonstrated APTT-N of >39 seconds and an APTT-N/SS ratio of >1.3. A C-reactive protein (CRP) level of ≥1.4mg/L demonstrated a significant positive correlation, with a higher APTT-N/SS indicating higher CRP levels. All 28 subjects receiving no anticoagulants and who had remaining specimens underwent a cross-mixing test (CMT). Of them, 17 were suspected for lupus anticoagulant (LA) by both the waveform shape and the index of circulating anticoagulant (ICA) value, 6 by the ICA value, and 5 were difficult to determine. This study revealed that the APTT-N prolongation correlated with CRP degree and the transient involvement of LA in CMT results due to CRP. This study indicated various reactivities depending on the assay reagents used. Further testing is warranted if LA is suspected, considering the patient's background.

Comparison of different algorithms for lupus anticoagulant detection: a single-center experience

BackgroundThe laboratory tests for lupus anticoagulant (LA) detection comprise complex and multistep coagulation testing procedures. There is no established gold standard assay or direct comparison of algorithms as recommended by different guidelines. ObjectivesThis study aimed to evaluate and compare the LA detection performance of different laboratory algorithms suggested by the existing guidelines. MethodsThe routine LA test data of 1801 plasma samples, including 188 LA-positive and 1613 LA-negative samples, were re-evaluated by applying the algorithms recommended by existing guidelines and were interpreted using various methods. Diagnostic performance indices for each LA detection algorithm were compared with those of the other algorithms. The efficacies of the different interpretation methods were analyzed to determine a suitable interpretation methodology for each assay. ResultsThe diagnostic performance for detecting LA varied by the algorithm and method of interpretation used. All laboratory algorithms displayed exceptional diagnostic performance with all diagnostic parameters of >90.0%. Nearly perfect agreement was observed in all algorithms when compared to the Clinical and Laboratory Standards Institute 2014 guideline interpreted by normalized screen-to-confirm ratio (NSCR) and mixing test–specific cutoff (MTC), as a reference assay (Cohen’s kappa coefficient, >0.90 [range, 0.94-1.00]). A combination of the index of circulating anticoagulant and NSCR was optimal for interpreting the activated partial thromboplastin time–based test, whereas a combination of the MTC and NSCR was suitable for the diluted Russell’s viper venom time–based test. ConclusionAll laboratory algorithms showed equivalent diagnostic performance. Establishing the best method of interpretation for each assay is recommended to improve LA detection performance.

Applying index of circulating anticoagulant to mixing tests with lupus anticoagulant screen and confirm reagents can distinguish with high specificity between lupus anticoagulants and direct factor Xa inhibitors.

Lupus anticoagulants (LA) are detected by prolongation of clotting times for dilute Russell's viper venom time (dRVVT) and activated partial thromboplastin time (APTT) screening tests. Direct oral anticoagulants (DOACs) can interfere with both screening and confirmatory tests. The present study aimed to investigate the influence of direct factor Xa inhibitors (DiXaIs) on screen, confirm and mixing tests and establish a method for differentiation from other sample types. A total of 257 samples including nonanticoagulated LA positive, LA positive with DiXaIs, factor deficiency, FVIII inhibitors, warfarin and non-APS DiXaIs were tested. APTT reagents Cephen LS/Cephen and dRVVT reagents LA1/LA2 were used, respectively, to screen/confirm the study group. Index of circulating anticoagulant (ICA) was calculated from clotting times based on the following formula as ICA screening and ICA confirmation. ICA= (1:1 Mix sample - Normal pooled plasma) / Screen patient x 100. An ICA matrix was established which suggested the presence of a DiXaI when both ICA screening and confirmation were above the cut-off. When only ICA screening is elevated, LA is suspected. Sensitivity and specificity of the ICA matrix were 52.2% and 92.8% for DiXaIs and 38.1% and 96.7% for LA in APTT, and 61.2% and 92.9% for DiXaIs and 22.2% and 88.4% for LA in dRVVT, respectively. The ICA matrix achieved high specificity with a lower apparent sensitivity for DiXaI samples comparatively to other devices but due only to less interferences: the matrix could contribute to differentiating DiXaIs from LA in samples where anticoagulation status is unknown.

Ruling out lupus anticoagulants with mixing test–specific cutoff assessment and the index of circulating anticoagulant

BackgroundLupus anticoagulant (LA) is classified in the antibody family that is recognized in antiphospholipid syndrome. Mixing tests are recommended for LA detection, and either a mixing test–specific cutoff (MTC) or index of circulating anticoagulant (ICA) is used for the interpretation. Although we previously showed MTC had higher sensitivity for LA than ICA, there are few studies investigating specificity. ObjectivesTo investigate specificity of multiple activated partial thromboplastin time (APTT) and diluted Russell's viper venom time (dRVVT) reagents for inhibitors using plasmas with non‐LA causes of prolonged clotting times, interpreted with MTC and ICA. MethodsSeventy‐six factor‐deficient samples (either artificially prepared, hereditary deficiency, or warfarin), and 12 inhibitors (either coagulation factor inhibitors, rivaroxaban, or apixaban) were used. Samples were tested with 4 APTTs, 1 dilute APTT (dAPTT), and 2 dRVVT reagents, and all elevated screen ratios were followed up with mixing tests. Frequencies of corrected and not‐corrected results were calculated. ResultsThe frequency of MTC and ICA corrected results, suggesting factor deficiency, were 5% to 43% and 79% to 100%, respectively, except for dAPTT, where MTC and ICA performed similarly. Frequencies of MTC and ICA not‐corrected results, suggesting inhibition, were 29% to 100% and 25% to 67%, respectively. ConclusionsThe data indicate that MTC has a tendency to generate not‐corrected mixing tests in factor‐deficient, warfarin, and other inhibitor samples, while ICA exhibited higher specificity. When we perform the mixing test and interpret the data, it is important to understand the characteristics of the indexes for maximizing the diagnostic potential of mixing test.

Mixing Studies in Patients With Prolonged Activated Partial Thromboplastin Time or Prothrombin Time.

Patients presenting for surgery may have isolated or combined prolonged activated partial thromboplastin time (aPTT) and/or prothrombin time (PT). In patients not receiving anticoagulants or with no identifiable cause for abnormal clot formation, a mixing study is performed. The index of circulating anticoagulant (ICA) has been used to predict the presence of an inhibitor, usually a lupus anticoagulant. We retrospectively reviewed the results of mixing studies performed at Northwestern Memorial Hospital, between January 1, 2010 and February 29, 2012. We determined the number of samples that normalized or remained prolonged, the clotting factors associated with prolonged test results, and the presence of coagulation inhibitors. We calculated the ICA in the samples with prolonged aPTT and PT to determine its ability to predict a lupus anticoagulant. The primary comparison of interest was the diagnostic utility of the ICA at cutoff values of 11% for predicting the presence of lupus anticoagulant. There were 269 mixing studies performed: 131 samples with prolonged aPTT; 95 with prolonged PT; and 43 with both prolonged aPTT and prolonged PT. Of the samples with a prolonged aPTT, 55 of 131 (42%) normalized, 36 of 131 (27%) partially corrected, and 40 of 131 (31%) remained prolonged. Thirty-three of 95 samples (35%) with prolonged PT normalized, while 62 of 95 (65%) remained prolonged. Eight of 43 (19%) mixing studies of patients with prolonged PT and aPTT normalized; the aPTT normalized, but the PT remained prolonged in 17 of 43 (39%); the PT normalized, but the aPTT remained prolonged in 7 of 43 (16%); and both tests remained prolonged in 11 of 43 (26%) samples. Prolongations in the aPTT were primarily associated with low activities of CF XII, while the majority of the prolongations in PT were secondary to low activities in CF VII. Combined prolongations were secondary to deficiencies in both the intrinsic and extrinsic as well as the common pathways. An ICA >11% had 100% (95% CI, 59%-100%) sensitivity, 53% (95% CI, 35%-70%) specificity, and 77% (95% CI, 62%-92%) accuracy in predicting the presence of lupus anticoagulant in patients with prolonged aPTT. Normalization of the aPTT and PT in a mixing study was associated with low clotting factor activity. The ICA may be helpful in predicting the presence of a lupus anticoagulant. As anesthesiologists take ownership of the perioperative surgical home, we need to understand the clinical implications of the results of mixing studies.

The issue of use parallelism factor method and index of circulating anticoagulant in diagnostic algorithm deficity of coagulation factors.

The paper presents the comparative use of algorithms to identify the causes of deficiency of coagulation factors in patients with a prolonged APTT, including the definition of the index of circulating anticoagulant (ICA) and the factor-parallelism (FP) method. The results obtained in children with hereditary hemophilia and adults with acquired hemophilia. It is shown that ICA is an effective method for pre-selection of patients with hereditary hemophilia if you suspect an inhibitor to subsequent confirmation test Bethesda. The method the FP has just proved itself in the diagnosis of acquired forms of hemophilia. The use of FP method is most expedient at the stage of screening to identify inhibitors in the laboratory. Method FP loses diagnostic value if the results of the activity factor in all dilutions is close to zero, which is characteristic for individual variants of hereditary hemophilia.

Evaluation of an automated algorithm for interpretation of lupus anticoagulant testing.

Lupus anticoagulant (LAC) testing is a multistep procedure including screening, mixing, and confirmation tests. STA Coag Expert is a software module for STA R Max and STA Compact Max analyzers which includes an on-demand LAC algorithm, based on ISTH guidelines, for automatic interpretation, calculation, and launch of assays in LAC interpretation ("Stago coag algorithm"). One hundred ninety four patient samples were analyzed in parallel and interpreted manually and automatically by LAC algorithms. LAC algorithms use identical flowcharts and cutoff values as in daily practice. Differently, it only uses index of circulating anticoagulant (ICA), whereas in routine also normalized ratios were assessed for interpretation of mixing tests. Interpretation of dRVVT and aPTT pathways and final conclusions were compared between both approaches. Compared to routine interpretation, LAC algorithm showed a sensitivity of 94% and a specificity of 100% for LAC detection, when discrepancies due to measured clotting times between both analyzers were excluded. Three false negatives were due to different interpretation of dRVVT mixing test. Discrepancies in interpretation of the aPTT mixing test (n=11) did not result in discrepant final LAC result, all having negative confirmation tests. No false positives were observed. With LAC algorithm, hands-on time reduced from 200 to 80minutes. The LAC algorithm of the STA Coag Expert shows good comparability to the manual interpretation of LAC and may be used to assist laboratories in automatic launching of additional tests and in interpretation of LAC according to ISTH guidelines. This way the STA Coag Expert LAC algorithm may improve interlaboratory and STA comparability of LAC results.

Lupus anticoagulant mixing tests for multiple reagents are more sensitive if interpreted with a mixing test‐specific cut‐off than index of circulating anticoagulant

Unlabelled Box BackgroundLupus anticoagulant (LA) is classified in the antibody family that is recognized as antiphospholipid antibodies. Guidelines for LA detection recommend mixing test interpretation with either a mixing test specific cut‐off (MTC) or index of circulating anticoagulant (ICA). We previously evidenced that MTC was superior to ICA in detecting the in vitro inhibition of LA with a single dilute APTT (activated partial thromboplastin time) and dRVVT (diluted Russell's viper venom time) pairing. ObjectivesThe objective in the present study was to compare the LA diagnostic effectiveness of MTC and ICA by multiple APTT and dRVVT reagents. MethodsOne hundred‐five samples from non‐anticoagulated patients positive for LA in the dilute APTT (dAPTT) and dRVVT reagent pairing employed for diagnostic examination were performed by undiluted and in a 1:1 mix with normal pooled plasma with four additional APTT reagents and another dRVVT reagent (dRVVT B). ResultsFrequencies of MTC and ICA positivity were determined from samples LA positive in undiluted plasma. MTC positivity in mixing test were 63%, 77%, 80%, 84%, 46%, 81%, and 72% in 4 APTT, dAPTT and 2 dRVVT, respectively. ICA positivity were 47%, 67%, 58%, 54%, 42%, 47%, and 29%, respectively. There were no samples of ICA‐positive/MTC‐negative with any reagent. ConclusionsThe data indicate that MTC is superior to ICA for LA detection in mixing tests in multiple reagents and reagent types. Although mixing tests may make weak LA samples appear negative, the efficacy of LA detection can be improved by the method to interpret the results.

Testing lupus anticoagulants in a real-life scenario - a retrospective cohort study.

IntroductionLupus anticoagulant (LAC) testing is challenging. Most data are derived from a well-controlled study environment with potential alterations to daily routines. The aim of this retrospective cohort study was to assess the capacity of various LAC screening tests and derived mixing tests to predict a positive result in subsequent confirmation tests in a large cohort of patients.Materials and methodsIn 5832 individuals, we retrospectively evaluated the accuracy of the aPTT-A, aPTT-LAscreen, aPTT-FS and dRVVTscreen and of their derived mixing tests in detecting a positive confirmation test result within the same blood specimen. The group differences, degree of correlation and the predictive accuracy of LAC coagulation tests were analysed using the Mann-Whitney U test, the Spearman-rank-correlation and by area under the receiver operating characteristic curve (ROC-AUC) analysis. ROC-AUCs were compared with the Venkatraman´s permutation test.ResultsThe pre-test probability of patients with clinically suspected LAC was 36% in patients without factor deficiency or anticoagulation therapy. The aPTT-LAscreen showed the best diagnostic accuracy with a ROC-AUC of 0.84 (95% CI: 0.82 – 0.86). No clear advantage of the dRVVT-derived mixing test was detectable when compared to the dRVVTscreen (P = 0.829). Usage of the index of circulating anticoagulant (ICA) did not improve the diagnostic power of respective mixing tests.ConclusionsAmong the parameters evaluated, aPTT-LAscreen and derived mixing test parameters were the most accurate tests. In our study cohort, neither other mixing test nor the ICA presented any further advantage in LAC diagnostics.

New formulas for mixing test to discriminate between lupus anticoagulant and acquired hemophilia A

IntroductionLupus anticoagulant (LA) is an antibody that interferes with in vitro coagulation reactions. The mixing test is considered useful for LA diagnosis and is also recommended to differentiate between acquired hemophilia A (AHA) and factor deficiency. However, there has been little study to differentiate between LA and AHA. Our aims are to investigate whether we can differentiate LA and AHA by the mixing test and to establish new formulas for the mixing test to differentiate these samples clearly. Materials and methodsWe examined 27 LA-positive, 29 coagulation factor deficient, 24 unfractionated heparin and 48 AHA samples. Index of circulating anticoagulant (ICA) values, calculated from the clotting times without incubation and after 2h incubation, were defined as ICA immediate (ICAi) and ICA delayed (ICAd) respectively. ICAd/ICAi and ICAd−ICAi were also calculated to compare the sensitivity and specificity. ResultsICAd/ICAi and ICAd−ICAi for AHA samples were significantly higher than those of the other sample groups. The sensitivities to AHA in ICAi, ICAd, ICAd/ICAi and ICAd−ICAi were 66.7%, 81.3%, 93.8% and 91.7% respectively, while the specificities for AHA were 45.0%, 66.3%, 85.0% and 98.8% respectively. ICAd/ICAi and ICAd−ICAi showed high sensitivity and specificity. ConclusionsICAd/ICAi and ICAd−ICAi were useful for LA and AHA diagnosis, because these could differentiate between LA and AHA samples. These new formulas can contribute to the rapid diagnosis and treatment of LA and AHA.

Mixing test specific cut-off is more sensitive at detecting lupus anticoagulants than index of circulating anticoagulant

IntroductionRecent guidelines for lupus anticoagulant (LA) detection recommend mixing test interpretation with either a mixing test-specific cut-off (MTC) or index of circulating anticoagulant (ICA). Few studies directly compare efficacy of these approaches. We retrospectively applied MTC and ICA assessment to raw data of 350 LA-positive plasmas from non-anticoagulated patients to compare detection rates of inhibition. Materials and methodsScreen and confirm dRVVT and dilute APTT assays were performed on undiluted plasma and 1:1 mixtures with normal pooled plasma. Samples were considered LA-positive if one or both screening test ratios were elevated and corrected by ≥10% with the confirmatory test. Mixing tests were assessed against locally derived cut-offs for MTC (dRVVT >1.13, dAPTT >1.15) and ICA (dRVVT >11.9%, dAPTT >13.2%). Results105 of 350 (30%) were positive in dRVVT and dAPTT, 109/350 (31.1%) were dRVVT positive only and 136/350 were dAPTT positive only (38.9%), from undiluted plasma results. Of the 214 dRVVT positive plasmas, 53 (24.8%) were negative for inhibition by MTC and 65 (30.4%) negative by ICA. Of the 241 dAPTT positive plasmas, 48 (19.2%) were negative by MTC and 97 (40.2%) negative by ICA. ConclusionWhilst integrated testing often detects LA without mixing tests they are diagnostically useful in certain circumstances. Thus, it is valuable to maximise mixing test interpretation as the dilution can lead to false-negative results. These data on a large cohort of LA-positive plasmas reveal that, with the reagents and equipment employed, MTC is superior to ICA in detecting the in vitro inhibition of LA.

Differences in lupus anticoagulant final conclusion through clotting time or Rosner index for mixing test interpretation.

Lupus anticoagulant (LAC) testing includes a screening, mixing and confirmation step. Although recently published guidelines on LAC testing are a useful step towards standardization, a lack of consensus remains whether to express mixing tests in clotting time (CT) or index of circulating anticoagulant (ICA). The influence of anticoagulant therapy, e.g. vitamin K antagonists (VKA) or direct oral anticoagulants (DOAC) on both methods of interpretation remains to be investigated. The objective of this study was to contribute to a simplification and standardization of the LAC three-step interpretation on the level of the mixing test. Samples from 148 consecutive patients with LAC request and prolonged screening step, and 77 samples from patients non-suspicious for LAC treated with VKA (n=37) or DOAC (n=30) were retrospectively evaluated. An activated partial thromboplastin time (aPTT) and dilute Russell's viper venom time (dRVVT) were used for routine LAC testing. The supplemental anticoagulant samples were tested with dRVVT only. We focused on the interpretation differences for mixing tests expressed as CT or ICA and compared the final LAC conclusion within each distinct group of concordant and discordant mixing test results. Mixing test interpretation by CT resulted in 10 (dRVVT) and 16 (aPTT) more LAC positive patients compared to interpretation with ICA. Isolated prolonged dRVVT screen mix ICA results were exclusively observed in samples from VKA-treated patients without suspicion for LAC. We recommend using CT in respect to the 99th percentile cut-off for interpretation of mixing steps in order to reach the highest sensitivity and specificity in LAC detection.

Research of the efficiency of different lupus anticoagulant assays

To provide valuable test by evaluating the efficiency of lupus anticoagulant assays based on different principles. 370 citrated samples were recruited, LA were tested by dRVVT, SCT, APTT-Actin, APTT-Actin FSL and APTT-SS respectively, and 1:1 mixing tests before incubation were studied in all the recruited subjects. For LA testing, the results of 1:1 mixing test were expressed as index of circulating anticoagulant (ICA), and the confirm test results were expressed as percent of correction (C) and normalized ratio (NR). The reference interval (RI)/Cut-off values of all the assays were established, and the efficiency of all the assays were further studied. The RI/Cut-off values of all assays were different. The sensitivity of dRVVT were the highest among all the assays (70.3%-93.1%), and the sensitivity of APTT (<55.0%) were the lowest. The sensitivity of APTT-SS (47.5%-53.5%) were higher than APTT-Actin (32.7%-39.6%) and APTT-Actin FSL (29.7%-36.6%). The specificity of dRVVT, SCT and three APTT were 91%-100%, 80.6%-100%, and 85.1%-98.5%, respectively. The specificity of SCT confirm test were 100%. Sensitivity of all the five methods were decreased in the weak positive LA. The sensitivity of dRVVT and SCT were more than 50.0%, however, the sensitivity of APTT-Actin and APTT-Acitn FSL were less than 16.0%. The sensitivity of APTT-SS were 23.7%-30.5%. Except the APTT-SS, dRVVT and SCT were correlated with thrombotic risk in APS patients (OR: 5.562-9.240, P<0.05). Every Laboratory should establish local LA RI/Cut-off values. dRVVT is the best assay for LA test, and APTT-SS method is superior to the other APTT method. The different test combinations of dRVVT and SCT are correlated with thrombotic risk in APS patients.

Verification of the guidelines for lupus anticoagulant detection: Usefulness of index for circulating anticoagulant in APTT mixing test

IntroductionLupus anticoagulant (LA) is an antibody that interferes with one or more in vitro coagulation reactions, which are dependent on interactions with protein-phospholipid complexes. For LA diagnosis, a mixing test is considered useful for differentiating the inhibitor from a factor deficiency. However, the usefulness and the index of circulating anticoagulant (ICA) in a mixing test with activated partial thromboplastin time (APTT) has not been adequately investigated, and there is scant information regarding the effects of warfarin, heparin, and hemophilia plasma on ICA. We evaluated the usefulness of ICA by investigating the correlation of that index with international normalized ratio (INR), heparin concentration, and factor VIII activity in hemophilia patients. Materials and MethodsWe examined samples from 28 patients positive for LA, 23 receiving warfarin, 19 receiving unfractionated heparin, and 29 with hemophilia A, as well as 61 normal samples. APTT-SLA, Actin FSL, APTT-SP, and PTT-LA were used as reagents in this study. ResultsThe correlation coefficient values between ICA and INR, heparin concentration, and factor VIII activity ranged from 0.031-0.342, 0.764-0.843, and 0.564-0.754, respectively, with the 4 reagents. The ICA values for the LA-positive samples were significantly higher than for the normal, warfarin, heparin, and hemophilia samples with all APTT reagents. Samples with a high heparin concentration above approximately 0.5U/ml showed ICA values greater than 15. ConclusionICA was able to distinguish LA-positive samples from the normal, warfarin, and hemophilia samples, but not heparin samples. ICA calculated from APTT clotting time is useful for LA diagnosis.

Frequent False‐positive results of lupus anticoagulant tests in plasmas of patients receiving the new oral anticoagulants and enoxaparin

Oral direct thrombin and Xa inhibitors are worldwide distributed for prevention and treatment of thrombosis. It is important to recognize their effects on lupus anticoagulant (LA) testing. The aim of the study is to describe the rate of false-positive results of LA tests on plasmas of patients with previous negative LA tests results that receive dabigatran etexilate (DAB) 110mg/twice a day, rivaroxaban (RIV) 10mg/day or 15mg/twice a day, or enoxaparin 40mg/day. Blood was taken between 1.5 and 4h post administration. Tests evaluated are as follows: prothrombin time, APTT, dilute Russell viper venom time (DRVVT) screen, APTT, and DRVVT mixing studies, index of circulating anticoagulant (ICA) with normal plasma, screen/confirm normalized ratio (NR) for DRVVT and silica clotting time (SCT). Plasmas from patients taking DAB (n=22) presented 100% prolonged APTT and DRVVT with ICA above the cutoff point and 81.8% positive screen/confirm NR, 100% prolonged SCT screen, but 4.5% positive confirmatory NR. All patients receiving RIV at 15mg/twice a day (n=4) presented positive DRVVT screen, mixing, and confirmatory tests, 75% and 100% prolonged APTT and SCT screen, with negative screen/confirm NR. Those taking RIV 10mg/day (n=22) showed 81.8% prolonged DRVVT screen, 82.3% and 76.5% of them with positive mixing and confirmatory studies. Patients receiving enoxaparin also presented high prevalence of APTT and DRVVT false-positive results. Dabigatran etexilate, RIV, and enoxaparin affect tests for LA not only in screening and mixing, but also in confirmatory studies. We considered that LA testing should not to be performed when patients are taken these drugs, particularly if blood is collected at peak, in order to avoid false-positive results.

C0118 Diagnostic difficulties for the detection of lupus anticoagulant: Experience of the hematology laboratory at Charles Nicolle Hospital of Tunis

The detection of lupus anticoagulant (LA) remains sometimes difficult in spite of considerable efforts made by the ISTH to standardize and simplify the diagnosis methods in courant practice. We report here our experience of various discrepancies found between the Screen/Confirm DRVVT (dilute Russell viper venom time) ratio and the index of circulating anticoagulant (ICA) according to Rosner with PTT-LA (Stago) in a series of 113 patients.

New guidelines for lupus anticoagulant: sensitivity and specificity of cut‐off values calculated with plasmas from healthy controls in mixing and confirmatory tests

The updated guidelines for lupus anticoagulant (LA) diagnosis indicate locally calculate the cut-off values of the index of circulating anticoagulant (ICA) and the clotting time in seconds (s) for mixing studies and % of correction (%C) for confirmatory tests. We assess sensitivity (SEN) and specificity (SPC) of the cut-off values obtained as the 99th percentile from 60 plasmas of healthy individuals. We analysed 647 plasmas from patients studied in the last 3 years, and results were revaluated according to the new criteria and cut-off values. Four hundred and three had LA, and 75 of them were under oral anticoagulants (OA). We performed three screening tests: activated partial thromboplastin time (APTT), diluted Russell viper venom time (dRVVT) and dilute prothrombin time (dPT), and previous diagnosis was carried out using our home-made cut-off calculated by receiver operating characteristics curves. We reanalysed the mixing and confirmatory data of APTT/dRVVT, the tests selected in the new guidelines. To evaluate SPC, 244 plasmas (160 OA and 84 congenital deficient patients) were studied. Considering mixing studies, the cut-off values demonstrate that SEN of ICA-APTT was 94% and of clotting time in second (s) 83%, with an SPC of 77% and 84%, respectively. For ICA-dRVVT, SEN was 72% and for clotting time in second (s) 77%, with SPC of 98% and 84%, respectively. The cut-off values for %C for confirmatory APTT show good SEN 82% and high SPC 96%; for confirmatory dRVVT lower SEN 77%, but a SPC of 100%. The combination of mixing and confirmatory tests interpreted according to the new guidelines can clearly differentiate LA from other coagulopathies.