Measurement of coagulation factor antibody levels is useful for diagnosis and determining therapeutic efficacy in hemorrhagic patients with autoantibodies to coagulation factor VIII and factor V: results from a single center in Japan.

Coagulation factor inhibitors (CFIs) sometimes cause fatal bleeding conditions. Determination of an inhibitor titer (INH-titer) using the Bethesda method is essential for diagnosing diseases associated with CFIs and examining the effects of immunosuppressive therapy. We reviewed 17 cases with CFIs (acquired hemophilia A, n = 11; FV inhibitor, n = 6) to examine the usefulness of determining quantities of an autoantibody to a coagulation factor (CF-IgG) by ELISA for diagnosis and therapeutic efficacy, as compared with INH-titer. One patient with an INH-titer and no evidence of CF-IgG was lupus anticoagulant (LA)-positive, and thus the positive INH-titer may have been a false positive caused by LA. Although INH-titer alone was insufficient to correctly identify patients with CFI, determination of CF-IgG appeared to be useful. In addition, even after INH-titer disappearance, hemorrhagic conditions recurred when CF-IgG was detected. These findings suggest that the presence of a clearance antibody against the coagulation factor might reduce the activity of that coagulation factor even after disappearance of the corresponding neutralizing antibody. Although the diagnosis and therapeutic efficacy can also be determined by INH-titer disappearance and improvement of corresponding coagulation factor activity, determination of CF-IgG by ELISA can improve the accuracy of these assessments.

Comparative evaluation of reagents for measuring protein S activity: possibility of harmonization.

Patients with congenital protein S (PS) deficiency show a hereditary predisposition for thrombosis, and PS deficiency is prevalent among Japanese populations. Diagnosis is based on symptoms of thrombosis and reduced PS activity. Three reagents that use different measurement principles for determining PS activity are available in Japan. This study aimed to confirm the possibility of harmonization of these three reagents to establish a universal standard for PS activity in Japanese populations. Commercial normal plasma and plasma samples obtained from healthy individuals and healthy pregnant women were tested at three facilities using three reagents for measuring PS: STA-Staclot Protein S (STA-PS), HemosIL Protein S (Clotting) (IL-PS), and a total PS assay (SNT-PS). The within-run precision of each reagent was good, as each had a coefficient of variation of ≤ 3.8%. The dilution linearity for each reagent was also good. The correlation coefficient was 0.94 for STA-PS vs. IL-PS, 0.93 for SNT-PS vs. STA-PS, and 0.90 for SNT-PS vs. IL-PS, indicating a good correlation. Although the three reagents available in Japan for measuring PS activity use different measurement methods, each showed good performance, and large differences were not observed between the obtained values. Harmonization among them appears possible.

Characterization of fibrin/fibrinogen degradation products reagents and their utility in critical care patients with enhanced fibrinolysis.

INTRODUCTION: Fibrin/fibrinogen degradation products (FDP) values reflect coagulation and fibrinolysis status, and FDP levels are helpful for diagnosis and classification of disseminated intravascular coagulation (DIC). FDP measurement has always played a key role in diagnosing DIC, a phenomenon that has recently gained renewed attention because of its occurrence in coronavirus disease 2019 (COVID-19) patients. Although the evaluation of FDP is crucial for the management of critical care, the variability among FDP reagents is unclear. In this study, we aimed to compare LIASAUTO P-FDP with three FDP reagents and investigate their characteristics. METHODS: In total, 172 plasmas samples were used in the correlation. The sample data were divided into three groups including negative, no and positive discrepancy based on the discrepancy percentages calculated from each correlation between LIASAUTO P-FDP and other three reagents. D-dimer, plasmin-α2 plasmin inhibitor complex (PIC), fibrin monomer complex (FMC), fibrinogen (Fbg) and Plasmin-α2 Plasmin Inhibitor (α2 PI) were measured and included in data analysis. RESULTS: The positive discrepancy groups showed higher D-dimer, PIC and FMC values than the negative discrepancy groups. The data indicated that LIASAUTO P-FDP had higher reactivity to D-dimer than other reagents and the values were elevated in the fibrinolysis-enhanced samples with various FDP fragments. CONCLUSION: LIASAUTO P-FDP displayed the reactivity towards various fibrin/fibrinogen degradation products, and it might be useful for DIC diagnosis because the fibrinolytic status differed in the DIC types and stages.

Expert consensus regarding standardization of sample preparation for clotting time assays.

Accurate clotting time assay results are vital, as the test is employed to indicate the amount of oral anticoagulant to be prescribed, while it is also used for screening the hemorrhagic and thrombotic diseases. The procedure chosen for preparation of a patient blood sample including centrifugation can contribute to significant differences in the results obtained. Thus, for the purpose of proposing a standardized method to appropriately prepare blood samples prior to assay, the Japanese Society of Laboratory Hematology organized the Working Group for Standardization of Sample Preparation for Clotting Time Assays (WG). Following reviews of previously announced guidelines and original experimental results, consensus was obtained by the WG, with the main findings as follows. (1) The recommended anticoagulant in the blood collection tube is sodium citrate solution at 0.105-0.109 M (3.13-3.2%). (2) Whole blood samples should be stored at room temperature (18-25 ˚C) within 1 h of collection from the patient. (3) For plasma preparation, centrifugation at 1500 × g should be performed for at least 15 min or at 2000 × g for at least 10 min at room temperature. (4) After the plasma sample is prepared, it should be stored at room temperature and assayed within 4 h.

Novel assay based on diluted prothrombin time reflects anticoagulant effects of direct oral factor Xa inhibitors: Results of multicenter study in Japan.

BACKGROUND: Direct oral anticoagulants targeting factor Xa (DXaIs) are administered as prophylaxis for various venothrombotic diseases without routine monitoring required. However, assessment of their anticoagulant effects is necessary to prevent severe events, including major bleeding and/or refractory thrombosis. OBJECTIVES: We examined the correlation of ratio of inhibited thrombin generation (RITG), determined using a novel assay based on dilute prothrombin time (dPT), with coagulant markers and laboratory test results to show drug effects. In addition, RITG usefulness as a confirmation test for DXaI therapy was investigated. METHODS: Citrated plasma samples were obtained from patients treated with rivaroxaban (n = 882), apixaban (n = 1214), or edoxaban (n = 820) at 4 different institutions in Japan. Laboratory tests, including prothrombin time (PT), activated partial thromboplastin time (APTT), D-dimer, and plasma concentrations of DXaIs, were conducted, with drug concentrations divided into peak and trough groups, within and after 5 h of administration. RESULTS: In each DXaI group, RITG was positively correlated with PT, APTT, and drug concentration, and negatively with D-dimer. RITG fluctuation during the peak and trough periods reflected the anticoagulant activity characteristic of each DXaI, which was different from blood concentration fluctuations. RITG showed a significant decrease in cases with thrombosis, while that was increased in those with hemorrhage. CONCLUSION: We developed RITG, a novel measurement method based on dPT. RITG represents residual coagulation ability in plasma samples, and is useful for assessment of bleeding and thrombotic tendencies in DXaI patients. RITG can be utilized to confirm the effectiveness of oral anticoagulation therapy with DXaI agents.

Knockdown of long noncoding RNA dreh facilitates cell surface GLUT4 expression and glucose uptake through the involvement of vimentin in 3T3-L1 adipocytes.

Glucose uptake in adipocytes is crucial for regulating systemic metabolism. Long noncoding RNAs (lncRNAs), defined as being transcripts with lengths exceeding 200 nucleotides that are not translated, are recently identified regulators of cellular functions. Previously, we have shown that an lncRNA, "down-regulated expression by hepatitis B virus X" (dreh), is involved in glucose transport in skeletal muscle cells. Here, we aimed to examine the involvement of dreh in glucose transport in 3T3-L1 adipocytes. Expression analysis showed that dreh was expressed in 3T3-L1 fibroblasts and adipocytes. Knockdown of dreh expression using its specific siRNAs lowered the glucose concentration of the medium and facilitated [3H]-2-deoxyglucose transport in adipocytes. Additionally, dreh silencing enhanced the protein expression of glucose transporter (GLUT4) in the plasma membrane of adipocytes. Treatment with siRNA against vimentin attenuated the glucose-lowering effect of dreh depletion. These results suggest that the repression of dreh facilitates glucose transport via increased GLUT4 expression in the plasma membrane through the involvement of vimentin in 3T3-L1 adipocytes. In conclusion, dreh is the first observed lncRNA that regulates glucose transport in adipocytes and could serve as a novel therapeutic target for diabetes by modulating adipocyte function. Considering the new function of dreh, we propose that dreh be renamed "down-regulated expression-related hexose/glucose transport enhancer."

Magnesium-dependent activated partial thromboplastin time assay-Simple method for lupus anticoagulant detection.

INTRODUCTION: Detection of lupus anticoagulant (LA), an antiphospholipid (aPL) antibody, in a clotting time test is an important finding for diagnosis of antiphospholipid syndrome (APS). However, confirmation of LA requires several different testing procedures, some of which can be difficult and require time. We report here a simple and highly specific method for detecting LA. MATERIALS AND METHODS: We examined 66 plasma samples obtained from LA-positive (LA) and 75 from LA-negative (non-LA) subjects, which included patients with acquired hemophilia and coagulation disorders, as well as from 43 healthy volunteer samples as normal controls. Activated partial thromboplastin time (APTT) was determined by adding 20 mmol of CaCl2 (Ca-APTT) or 25 mmol of a mixture of Mg and Ca (Mg-APTT). The ratio of Mg-APTT/Ca-APTT was then calculated and used as the Mg/Ca Index. RESULTS: The Mg/Ca Index value for the LA group was significantly lower than that for the non-LA and normal control groups (P < .0001). When the cutoff value of the Mg/Ca Index was less than 1.00, the sensitivity of LA determination using the Mg-APTT assay was 80.3%, while specificity was 100%. CONCLUSION: Our findings indicate that the present Mg-APTT assay is a simple yet highly specific method for LA detection.

Dreh, a long noncoding RNA repressed by metformin, regulates glucose transport in C2C12 skeletal muscle cells.

AIMS: The anti-hyperglycemic action of metformin on skeletal muscles is presently unclear. Long noncoding RNAs (lncRNAs) are implicated in multiple cellular functions. This study aims to explore the role of lncRNAs in the glucometabolic action of metformin on skeletal muscle cells. MAIN METHODS: Metformin accumulation was assessed using [14C]-metformin. A lncRNA array was used to investigate metformin-regulated lncRNAs in C2C12 skeletal muscle cells. Knockdown studies were applied to evaluate the function of lncRNA Dreh. A colorimetric assay was used for the measurement of medium glucose concentration; glucose transport was assessed using [3H]-2-deoxyglucose; real-time PCR was used for RNA expression analysis, and western blotting was used to assess protein expression in myotubes. A Dreh overexpression plasmid was transfected into the cells. KEY FINDINGS: Metformin accumulated in C2C12 myotubes. Metformin reduced medium glucose concentration and repressed lncRNA Dreh expression in the myotubes. Knockdown of Dreh in the myotubes resulted in reduced glucose concentration in the culture medium, increased glucose transport, and increased levels of GLUT4 protein in the plasma membrane. Overexpression of Dreh attenuated the glucose-lowering effect of metformin in myotubes. SIGNIFICANCE: The glucoregulatory actions of metformin are mediated in part by a lncRNA, Dreh, in the skeletal muscle cells. Dreh is a novel regulator for glucose transport and could be a therapeutic target for diabetes.

Lupus anticoagulant-hypoprothrombinemia syndrome and similar diseases: experiences at a single center in Japan.

Patients with lupus anticoagulant (LA), a thrombotic risk factor, along with decreased prothrombin (FII) activity are classified as lupus anticoagulant-hypoprothrombinemia syndrome (LAHPS) and occasionally show bleeding symptoms, although this is not essential for diagnosis. We treated 20 cases of LAHPS over a 3-year period. Median FII activity was 20.9% and the anti-prothrombin antibody (anti-II Ab), shown by ELISA findings, was detected in 55%. Bleeding symptoms were observed in 20%, although that finding was not correlated with FII activity or anti-FII Ab quantity. We also observed 21 LA cases with decreased activity of coagulation factors other than FII, which we have designated LAHPS-like syndrome (LLS). Among LLS patients, anti-FII Ab and bleeding symptoms were seen in 47.6% and 14.3%, respectively. Our findings suggest that bleeding in LAHPS and LLS cannot be explained only by FII activity decreased by anti-FII Ab. Low FVIII activity and the anti-FVIII antibody (anti-FVIII Ab) were detected in some LAHPS and LLS patients, making it difficult to distinguish those from acquired hemophilia A cases. Detection of anti-FVIII Ab quantity by ELISA may be useful for accurate determination, as that was not performed in our LAHPS or LLS patients.

Basic Evaluation of the Newly Developed "Lias Auto P-FDP" Assay and the Influence of Plasmin-α2 Plasmin Inhibitor Complex Values on Discrepancy in the Comparison with "Lias Auto D-Dimer Neo" Assay.

BACKGROUND: Laboratory determination of fibrin/fibrinogen degradation products (FDP) levels, along with that of the D-dimer, is important for assessing the fibrinolytic situation. Recently, we developed a new FDP reagent "Lias Auto P-FDP", which can detect various FDP fragments. The purpose of this study was to evaluate the basic performance of the newly developed Lias Auto P-FDP and compare it with Lias Auto D-Dimer Neo assay. METHODS: The within-run precision of Lias Auto P-FDP and Lias Auto D-Dimer was determined 20 times in low and high value controls. The between-day precision was evaluated five times a day for five days. The linearity study was performed by diluting high value samples for 2 - 10-fold and 2 - 8-fold. The comparative study was performed using 172 patient samples with elevated FDP values. For the discrepancy analysis, the samples were divided into three groups by the discrepancy percentage between the FDP and D-dimer values. The groups were defined as follows: lower discrepancy group, less than -20%; no discrepancy group, -20% to 20%; upper discrepancy group, more than 20%. RESULTS: The coefficient of variation % (CV%) in within-run and between-day precision were within 3.8% for both FDP and the D-dimer. The correlation coefficients were more than 0.999 and the linearity was high. In the comparative study, the values of FDP were higher than that of the D-dimer in all samples. The median FDP and D-dimer values of lower discrepancy, no discrepancy, and upper discrepancy groups were 11.8, 20.3, and 51.4, and 8.0, 11.3, and 13.1, respectively. FDP showed an increasing tendency but D-Dimer showed constant values. Thus, the possible cause of discrepancy between FDP and D-dimer values were the elevated FDP values. In addition, the values of plasmin-α2 plasmin inhibitor complex (PIC) in the upper discrepancy group were higher than that of the lower and no discrepancy groups, indicating progression of fibrinolysis. CONCLUSIONS: In this study, we evaluated the newly developed Lias Auto P-FDP reagent and confirmed that the basic performance was acceptable. FDP was elevated in samples with high PIC values, which indicated progression of fibrinolysis. Determination of fibrinolysis conditions by FDP measurement is important.

Sarcolipin expression is repressed by endoplasmic reticulum stress in C2C12 myotubes

Sarcolipin is a transmembrane protein expressed in the sarco/endoplasmic reticulum of skeletal and atrial muscles in large animals. Sarcolipin plays crucial roles in heat production through modifying the function of sarco/endoplasmic reticulum Ca2+ ATPase, thereby being involved in thermogenesis and systemic metabolism. In skeletal muscle, endoplasmic reticulum (ER) stress has been implicated in several conditions, such as insulin resistance, muscle diseases, and hypo/hyper-contraction. Here, we investigated the effect of ER stress on sarcolipin expression in skeletal muscle cells, C2C12 myotubes. First, gene expression of sarcolipin was confirmed in the cells during myogenesis. Then, ER stress was induced in C2C12 myotubes by treatment with tunicamycin or thapsigargin. Sarcolipin messenger RNA (mRNA) and protein expression were significantly reduced by ER stress induction. The reduction was independent of inositol-requiring element 1 (IRE1), which is activated by ER stress and has potent endonuclease activity, when evaluated by treatment with an IRE1 inhibitor, 4μ8C. On the other hand, sarcolipin mRNA stability was reduced under the ER stress when evaluated by treatment with actinomycin D. In conclusion, these results show that ER stress represses sarcolipin expression due to changes in mRNA stability in C2C12

Sarcolipin expression is repressed by endoplasmic reticulum stress in C2C12 myotubes.

Sarcolipin is a transmembrane protein expressed in the sarco/endoplasmic reticulum of skeletal and atrial muscles in large animals. Sarcolipin plays crucial roles in heat production through modifying the function of sarco/endoplasmic reticulum Ca2+ ATPase, thereby being involved in thermogenesis and systemic metabolism. In skeletal muscle, endoplasmic reticulum (ER) stress has been implicated in several conditions, such as insulin resistance, muscle diseases, and hypo/hyper-contraction. Here, we investigated the effect of ER stress on sarcolipin expression in skeletal muscle cells, C2C12 myotubes. First, gene expression of sarcolipin was confirmed in the cells during myogenesis. Then, ER stress was induced in C2C12 myotubes by treatment with tunicamycin or thapsigargin. Sarcolipin messenger RNA (mRNA) and protein expression were significantly reduced by ER stress induction. The reduction was independent of inositol-requiring element 1 (IRE1), which is activated by ER stress and has potent endonuclease activity, when evaluated by treatment with an IRE1 inhibitor, 4µ8C. On the other hand, sarcolipin mRNA stability was reduced under the ER stress when evaluated by treatment with actinomycin D. In conclusion, these results show that ER stress represses sarcolipin expression due to changes in mRNA stability in C2C12 myotubes.

[Development of acquired hemophilia A during maintenance therapy for immune thrombocytopenia].

Acquired hemophilia A (AHA) is a rare coagulation disorder caused by autoantibodies against coagulation factor VIII (FVIII). We report herein a very rare case of AHA complicated by immune thrombocytopenia (ITP). A 30-year-old woman was hospitalized with severe thrombocytopenia. Her platelet count was 5,000/µl on admission, at which time APTT was normal. ITP was diagnosed and she was treated with γ-globulin, platelet transfusion, and prednisolone at 1 mg/kg/day. She was discharged after platelet count normalization and prednisolone was tapered to 5 mg/day. During the prednisolone tapering, purpura appeared on both thighs and in the left inguinal region, and APTT was found to be prolonged. She was referred to our hospital for examination of APTT prolongation. FVIII activity was markedly decreased to 7.7% and the FVIII inhibitor was positive (1.5 BU/ml), based on which AHA was diagnosed. We carefully followed this patient without intensification of immunosuppressive therapy for 7 weeks, but her platelet count decreased from 150,000/µl to 70,000/µl and the FVIII inhibitor increased to 4 BU/ml. We therefore increased prednisolone to 30 mg/day, after which her platelet count increased and complete remission of AHA was achieved by day 42. In addition, we examined the relationship of the FVIII inhibitor and FVIII binding antibody in this case.

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

INTRODUCTION: Lupus 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 METHODS: We 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. RESULTS: ICAd/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. CONCLUSIONS: ICAd/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.

[A Case of Lupus Anticoagulant-Hypoprothrombinemia Syndrome with Phosphatidylserine-Dependent Anti-Prothrombin Antibody].

Lupus anticoagulant-hypothrombinemia syndrome (LAHS) is a rare disease involving hemorrhagic diathe- sis due to hypothrombinemia with lupus anticoagulant. We report a 28-week-pregnant woman at twenty years of age, who had been hospitalized with jaundice. In laboratory data, AST, ALT, and bilirubin were elevated and the prothrombin time (PT) and activated partial thromboplastin time (APTT) were prolonged. Although the liver failure was improved after she delivered a baby by Caesarean section, postoperative intraperitoneal bleeding persisted. The diagnosis by liver biopsy was autoimmune hepatitis. Although the bleeding was stopped on the seventh postoperative day, the prolongation of PT and APTT remained. LA was positive in the diluted Russell's viper venom time. Anti-cardiolipin and anti-beta-2-glycoprotein anti- bodies were also positive. The prothrombin activity was reduced. A high titer of phosphatidylserine- dependent antiprothrombin antibody (aPS/PT), which causes bleeding, was observed. Based on these data, she was diagnosed with LAHS. The liver dysfunction and prolongation of PT and APTT were normalized following the administration of corticosteroids. In this case, aPS/PT may have contributed to the pathological physiology of LAHS. [Case Report].

Low levels of plasma protein S, protein C and coagulation factor XII during early pregnancy and adverse pregnancy outcome.

It was the study objective to evaluate whether low levels of plasma protein S (PS) activity, free PS, protein C (PC) activity and coagulation factor XII (FXII) during early pregnancy are related to adverse pregnancy outcomes. Peripheral blood samples were obtained at 8-14 gestational weeks (GW) from a consecutive series of 1,220 women. The levels of plasma PS activity, free PS, PC activity, and FXII were measured. Cut-off values were defined as < 1st, < 5th, and < 10th percentiles of values obtained from 933 women whose pregnancies ended in normal deliveries without complications. PS activity of < 10th percentile yielded risks of pregnancy-induced hypertension (PIH) and severe PIH, while free PS level of < 5th percentile yielded a risk of pre-eclampsia. FXII level of < 1st percentile yielded a risk of premature delivery (PD) at < 34 GW. None was associated with PD at < 37 GW, fetal growth restriction or fetal loss. A multivariate analysis demonstrated that PS activity of < 10th percentile (odds ratio 5.9, 95 % confidence interval 1.7-18.1) and body mass index (BMI) ≥ 25 kg/m² (4.3, 1.1-13.3) were independent risk factors for severe PIH. Similarly, free PS level of < 5th percentile (4.4, 1.0-14.3) and BMI ≥ 25 kg/m² (4.0, 1.3-10.9) were independent risk factors for pre-eclampsia. In conclusion, women with low levels of plasma PS activity and free PS during early pregnancy might have increased risks of PIH, severe PIH or pre-eclampsia. Women with low FXII level might have an increased risk of PD at < 34 GW.

[Pathogenesis and Laboratory Findings in Antiphospholipid Syndrome, Especially Associated with Lupus Anticoagulant].

Antiphospholipid syndrome (APS), an acquired thrombotic condition, is a complex clinical state characterized by the presence of circulating antiphospholipid antibodies in patients with thrombosis or pregnancy morbidity. Revised APS classification criteria are used for diagnosis, which include at least one clinical criterion (thrombosis or pregnancy loss) and at least one of the laboratory criteria [anticardiolipin antibodies, anti-ß2GPI antibodies, lupus anticoagulant (LA)]. LA is also an independent risk factor for developing thrombosis, though some LA-positive cases have been reported to have a bleeding symptom. Lupus anticoagulant-hypoprothrombinemia syndrome (LAHPS) is a rare disorder characterized by a bleeding tendency due to low prothrombin activity in patients with LA, and has recently been reported not only in children but also in adults We have encountered LA cases with bleeding and low coagulation factor activities except for prothrombin. Based on our findings, we propose that LA-positive cases with a bleeding symptom and characterized by low coagulation factor activity including prothrombin be termed lupus anticoagulant-associated coagulopathy (LAAC). Furthermore, coagulation factor autoantibodies are often detected in LAAC patients; thus, correct measurement of LA is important to distinguish LAAC patients from those possessing an inhibitor to coagulation factors such as acquired hemophilia A as well as to select the optimal therapeutic strategy.

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

INTRODUCTION: Lupus 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 METHODS: We 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. RESULTS: The 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. CONCLUSION: ICA 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.