Newly developed dilute Russell's viper venom reagents for lupus anticoagulant detection with improved specificity.

Background Dilute Russell's viper venom time (dRVVT) is indispensible in lupus anticoagulant (LA) detection yet commercial reagents from different suppliers perform variably, no gold standard assays exist and therapeutic anticoagulation interference is problematic. Objective The objective of this study was to compare a new formulation dRVVT with two currently available dRVVTs. Materials and methods Life Diagnostics (LD) dRVVT and Stago PTT-LA were routinely used for lupus anticoagulant detection, plus Taipan snake venom time/ecarin time (TSVT/ET) for patients on warfarin or rivaroxaban. Siemens dRVVT and the new HYPHEN BioMed (HBM) dRVVT were tested with 193 patient samples. Group 1, 59 non-anticoagulated patients (NAPs) LA-positive in LD dRVVT; Group 2, 15 PTT-LA-positive/dRVVT-negative NAPs; Group 3, 24 LA-positive warfarinized patients; Group 4, 13 patients on rivaroxaban; Group 5, 62 LA-negative thrombotic NAPs; Group 6, 20 warfarinized, non-antiphospholipid syndrome patients. Results Accepting that the Life Diagnostics reagents were acting as a pseudo-gold standard, Siemens dRVVT detected 56/59, (95%) Group 1 LA and HBM dRVVT 46/59, (76%), one each from Group 2, and Siemens dRVVT detected one in Group 5. The lower HBM dRVVT detection rate mainly concerned weaker LA, where between-reagent concordance is problematic. All Group 3 patients appeared LA-positive in undiluted plasma with Siemens dRVVT, as did 16/24 (67%) with HBM dRVVT but the fewer LA-positives in mixing tests better mapped to clear LA-positives with LD dRVVT. LD and Siemens dRVVTs exhibited 87% and 95% false-positivity for Group 6 whilst HBM dRVVT had none. Increasing the cut-off improved accuracy. Applying higher cut-offs improved accuracy in Group 4 patients. Conclusion HBM dRVVT exhibited improved specificity, mainly due to less interference by anticoagulation, but reduced sensitivity, compared to the other dRVVTs employed.

Qualification of a select one-stage activated partial thromboplastin time-based clotting assay and two chromogenic assays for the post-administration monitoring of nonacog beta pegol.

Essentials Nonacog beta pegol (N9-GP) is an extended half-life, recombinant human factor IX (FIX). One-stage clotting (OSC) and chromogenic FIX activity assays were assessed for N9-GP recovery. OSC STA® -Cephascreen® , ROX FIX and BIOPHEN FIX chromogenic assays were qualified for N9-GP. Other extended half-life factor products should be assessed in a similar way prior to approval. SUMMARY: Background Nonacog beta pegol (N9-GP) is an extended half-life, glycoPEGylated recombinant human factor IX that is under development for the prophylaxis and treatment of bleeding episodes in hemophilia B patients. Considerable reagent-dependent variability has been observed when one-stage clotting assays are used to measure the recovery of recombinant FIX products, including N9-GP. Objective To qualify select one-stage clotting and chromogenic FIX activity assays for measuring N9-GP recovery. Methods The accuracy and precision of the one-stage clotting assay (with the STA-Cephascreen activated partial thromboplastin [APTT] reagent) and the ROX Factor IX and BIOPHEN Factor IX chromogenic assays for measuring N9-GP recovery were assessed in N9-GP-spiked hemophilia B plasma samples in a systematic manner at three independent sites, with manufacturer-recommended protocols and/or site-specific assay setups, including different instruments. Results For each of the three FIX activity assays qualified on five different reagent-instrument systems, acceptable intra-assay and interassay accuracy and precision, dilution integrity, reagent robustness and freeze-thaw and short-term sample stabilities were demonstrated. The STA-Cephascreen assay showed a limited reportable range at one of the three qualification sites, and the BIOPHEN Factor IX assay showed suspect low-end sensitivity at one of the three qualification sites. An individual laboratory would account for these limitations by adjusting the assay's reportable range; thus, these findings are not considered to impact the respective assay qualifications. Conclusion The one-stage clotting assay with the STA-Cephascreen APTT reagent, the ROX Factor IX chromogenic assay and the BIOPHEN Factor IX chromogenic assay are considered to be qualified for the measurement of N9-GP in 3.2% (0.109 m) citrated human plasma.

Hyperhomocyst(e)inemia and endothelial dysfunction in IDDM.

OBJECTIVE: While elevated blood levels of homocyst(e)ine represent an independent risk factor for macrovascular disease, we assessed the link between hyperhomocyst(e)inemia and diabetic microvascular diseases. RESEARCH DESIGN AND METHODS: Plasma levels of homocyst(e)ine and thrombomodulin (TM), markers of endothelial cell damage, were measured before and 3 h after oral methionine loading in 75 patients with IDDM and 40 healthy control subjects matched for sex and age. Exclusion criteria were hyperlipidemia, hypertension, smoking, or positive family history for cardiovascular disease. RESULTS: IDDM patients had higher pre- and postload plasma levels of homocyst(e)ine than did healthy control subjects (12.0 vs. 7.7 mumol/l and 27.6 vs. 16.0 mumol/l; P < 0.001). Of 75 IDDM patients, 26 had plasma homocyst(e)ine levels above the normal range (means +/- 2 SD of values obtained in the control group). These IDDM patients with hyperhomocyst(e)inemia had higher plasma TM levels (62.2 vs. 38.2 ng/ml, P < 0.001), higher albumin excretion rates (485 vs. 115 mg/l, P < 0.005), and a higher prevalence of late diabetic complications (nephropathy, 76 vs. 33%; retinopathy, 69 vs. 51%; neuropathy, 57 vs. 41%; and macroangiopathy, 57 vs. 33%) compared with IDDM patients with normal plasma homocyst(e)ine. In vitro experiments with human umbilical vein cells showed an increased release of TM into the culture supernatant only when endothelial cells were pretreated with advanced glycation end product (AGE)-albumin before L-homocystine was added. A synergistic action of homocyst(e)ine and AGEs might contribute to vascular complications in patients with diabetes. CONCLUSIONS: Hyperhomocyst(e)inemia is common in nephropathic diabetic patients and may contribute to the enhanced morbidity and mortality from cardiovascular diseases characteristically observed in IDDM patients with diabetic nephropathy.

Hyperhomocyst(e)inemia and endothelial dysfunction in IDDM.

OBJECTIVE: Considering that elevated blood levels of homocyst(e)ine represent a known independent risk factor for macrovascular disease, we assessed the link between hyperhomocyst(e)inemia and diabetic microvascular complications. RESEARCH DESIGN AND METHODS: Homocyst(e)ine and thrombomodulin plasma levels, a marker of endothelial cell damage, were measured before and 3 h after oral methionine loading in 75 patients with stable, well-controlled IDDM and 40 healthy control subjects matched for sex and age. Exclusion criteria were hyperlipidemia, hypertension, smoking, or positive family history for cardiovascular disease. RESULTS: IDDM patients had higher pre- and postload homocyst(e)ine plasma levels than did healthy control subjects (12.0 vs. 7.7 mumol/l and 27.6 vs. 16.0 mumol/l; P < 0.001). Of 75 IDDM patients, 26 had homocyst(e)ine plasma levels above the normal range (defined as mean +2 SD of values obtained in the control group). The IDDM patients with hyperhomocyst(e)inemia had higher thrombomodulin plasma levels (62.2 vs. 38.2 ng/ml; P < 0.001), higher albumin excretion rates (485 vs. 115 mg/l; P < 0.005), and a higher prevalence of late diabetic complications (nephropathy, 76 vs. 33%; retinopathy, 69 vs. 51%; neuropathy, 57 vs. 41%; macroangiopathy, 57 vs. 33%) compared with IDDM patients with normal plasma homocyst(e)ine. In vitro experiments with human umbilical vein cells show an increased release of thrombomodulin into the culture supernatant only when endothelial cells were pretreated with advanced glycation end product (AGE)-albumin before L-homocystine was added. A synergistic action of homocyst(e)ine and AGEs might contribute to vascular complications of patients with diabetes. CONCLUSIONS: Hyperhomocyst(e)inemia is common in nephropathic diabetic patients and may contribute to the enhanced morbidity and mortality from cardiovascular diseases characteristically observed in IDDM patients with diabetic nephropathy.

Thrombomodulin is synthesized by osteoblasts, stimulated by 1,25-(OH)2D3 and activates protein C at their cell membrane.

We have previously shown that protein S, a vitamin K-dependent protein, is a bone matrix component synthesized and secreted by osteoblasts. Because protein S is a cofactor of protein C in inhibiting factor Va and VIIIa, we have looked for the presence of the proteins related to the anticoagulant protein C system in human MG 63 osteosarcoma cells and in human adult osteoblast-like cells. Using immunoblotting, we have shown that protein C, factor V, and C4b binding protein are not secreted by these cells. We have shown by enzyme-linked immunoassay, immunocytochemistry, and immunoprecipitation of labeled proteins that thrombomodulin, a transmembrane glycoprotein involved with thrombin in the activation of protein C, is present at the cell surface of osteoblasts. Moreover, using a protein C activation system where thrombin and protein C are added to the cells, we have shown that protein C could be activated at the osteoblast cell surface. This activation of exogenous protein C, reflecting the activity of thrombomodulin, as well as the expression of the thrombomodulin antigen, is regulated by some bone resorption-enhancing factors. 1,25-dihydroxyvitamin D3 and retinoic acid increase thrombomodulin expression and activity in a dose-dependent manner whereas tumor necrosis factor alpha and interleukin 1 decrease these parameters. Because thrombomodulin is known to inhibit single-chain urokinase-type plasminogen activator, a molecule present in the osteoblast microenvironment, these findings suggest that thrombomodulin could play a role in the regulation of bone resorption by modulating the plasmin system.

Antigens involved in heparin-induced thrombocytopenia.

Heparin-induced thrombocytopenia (HIT), a common side effect of heparin therapy, can be life-threatening. Following treatment with heparin, platelet factor 4 (PF4) is released into the circulation. Heparin can bind to PF4 to form a reactive antigen on the platelet. The formation of large heparin-PF4 (H-PF4) complexes that can react with HIT antibodies depends on the concentrations of heparin and PF4. Antibodies involved in HIT are usually of the IgG class, but can be IgA or IgM; Fab and Fc fragments are necessary for the activation of platelets. In a minority of cases of HIT, antibodies to H-PF4 are not present, but antibodies to other cytokines have been found. These antibodies frequently react either with interleukin-8 (IL-8) or with neutrophil-activating peptide 2 (NAP-2). Discontinuation of heparin has been the traditional first step in the treatment of HIT. Drugs that inhibit thrombin directly may be necessary in some cases.

Thrombospondin (TSP1) mediates in vitro proliferation of human MG-63 osteoblastic cells induced by alpha-thrombin.

Thrombospondin (TSP) is a 450-kDa glycoprotein synthesized and secreted by human MG-63 osteoblastic cells. In this study, we have first studied the effect of alpha-thrombin on TSP expression by human MG-63 cells. In situ hybridization indicated that TSP mRNA level in thrombin-treated MG-63 cells was increased when compared to unstimulated cells. As judged by immunofluorescence, thrombin-treatment of MG-63 cells resulted in increased cell surface expression of TSP when compared to quiescent cells. Because thrombin stimulates proliferation of osteoblastic cells, the involvement of TSP in proliferation of thrombin-stimulated osteoblastic cells was then investigated using a serum-free mitogenesis assay. Both alpha-thrombin (0.01 to 0.15 U/ml) and TSP (5 to 600 ng/ml) caused a dose-dependent increase in [3H]thymidine incorporation by MG-63 cells. Proliferation of osteoblastic cells induced by alpha-thrombin or TSP was specifically and totally inhibited by anti-TSP monoclonal antibodies (3-10 micrograms/ml) or by indomethacin (1 microM), an inhibitor of prostaglandin synthesis. Anti-TSP antibodies which inhibited cell proliferation also inhibit TSP expression to the surface of these cells. Our experiments support the existence of a mechanism whereby TSP bound to the cell surface of thrombin-treated MG-63 cells stimulates secretion of prostaglandins which, in turn, allow cell proliferation to proceed.

The growth-supportive effect of thrombospondin (TSP1) and the expression of TSP1 by human MG-63 osteoblastic cells are both inhibited by dexamethasone.

Thrombospondin (TSP) is a 450-kDa extracellular matrix glycoprotein which supports the growth of human MG-63 osteoblastic cells [Abbadia et al., FEBS Lett., 329 (1993) 341-346]. In this study, we describe the effect of the glucocorticoid, dexamethasone, on cell proliferation and TSP expression by MG-63 cells. Using a serum-free mitogenesis assay, dexamethasone (25 to 500 nM) caused a dose-dependent decrease in [3H]thymidine incorporation by MG-63 cells in culture, reaching 40% inhibition of cell proliferation at a concentration of 250 nM. Similarly, the stimulatory effect of TSP (500 ng/ml) on proliferation of MG-63 cells was totally abolished in the presence of dexamethasone (250 nM). In situ hybridization indicated that TSP mRNA level in dexamethasone-treated MG-63 cells decreased compared to quiescent cells. As judged by fluorescence-activated cell sorting analysis, dexamethasone treatment of MG-63 cells resulted in a 50 to 70% decrease in TSP cell surface expression compared to quiescent cells. Secretion of TSP in the culture fluid of dexamethasone-treated MG-63 cells also decreased by 40% while, under similar experimental conditions, a 180% increase in alkaline phosphatase activity was observed in dexamethasone-treated cells. Because glucocorticoids induce osteoporosis in vivo and reduce proliferation of osteoblasts in vitro, our results argue for an important role of TSP during bone formation.

Poor anticoagulant response to tissue factor pathway inhibitor in patients with venous thrombosis.

Tissue factor pathway inhibitor (TFPI) is of major importance in regulating the coagulation triggering effects of tissue factor. An association between TFPI deficiency and thrombosis has still not been clearly demonstrated. We evaluated the anticoagulant activity of exogenous TFPI added either to the plasma of patients with venous thrombosis (n = 118) or to the plasma of healthy controls similar in terms of mean age and sex ratio (n = 107). A poor anticoagulant response to TFPI, defined as TFPI resistance, was observed in 4.7% of controls and in 11.0% of patients. TFPI resistance was associated with an almost threefold increase in the risk of thrombosis and could therefore represent a novel hemostatic risk factor for venous thrombosis.

Differences in free and total tissue factor pathway inhibitor, and tissue factor in peripheral artery disease compared to healthy controls.

Tissue factor (TF) is one of the major initiators of coagulation and raised plasma levels have been found in various cardiovascular diseases. TF activity is, however, regulated by tissue factor pathway inhibitor (TFPI), and alteration in levels of TF and/or TFPI may thus relate to thrombogenesis and atherogenesis. To investigate possible abnormalities in TF and free TFPI (i.e. unbound to TF) and total TFPI among patients with peripheral artery disease (PAD), we studied 42 patients (mean age 57, 35 men) with objectively proven (by ABPI/Doppler) disease and 42 age- and sex- matched healthy controls. TF, free TFPI and total TFPI were measured in citrated plasma by ELISA. TF was higher in the patients with PAD compared to controls (275+/-122 pg/ml versus 158+/-60, P<0.0001) but levels of total TFPI were lower in the patients (43+/-10 ng/ml versus 50+/-15, P=0.021). There was no significant difference in levels of free TFPI between patients and controls (7.2+/-1.5 ng/ml in controls, 7.5+/-1. 6 among patients, P=0.39). Within the control patients, levels of free and total TFPI were significantly correlated (Spearman r=0.51, P=0.001) but in the patients with PAD this correlation was poor (r=0. 21, P=0.178). We suggest that reduced levels of total TFPI and raised levels of TF may contribute to the process of atherogenesis and the increased risk of thrombosis among patients with cardiovascular disease.

Endothelial dysfunction during acute methionine load in hyperhomocysteinaemic patients.

Hyperhomocysteinaemia has been associated with arterial and venous thrombosis possibly by causing damage to the endothelium. We hypothesised that an oral load in methionine, that increases plasma homocysteine, would also result in an increase in biological markers of endothelial or platelet dysfunction. Then we investigated two groups of patients with arterial or venous occlusive disease: 17 with hyperhomocysteinemia and 12 without hyperhomocysteinemia. We measured in both groups plasma soluble thrombomodulin, von Willebrand factor, P-selectin and tissue factor plasma inhibitor before and 6 hours after a load with 100 mg/kg oral methionine. Methionine load resulted in a significant increase in von Willebrand factor in both groups (P<0.02), suggesting that endothelial dysfunction occurs during the load.

Protein C level at birth.

The protein C level was determined, on cord blood, for 30 healthy newborns by electro-immuno assay using a monospecific antiserum. For the newborns the mean level of protein C related antigen is about one third of normal adults' mean level. There is a good correlation between Protein C related antigen and prothrombin related antigen. The low level of these vitamin-K-dependent proteins is probably a consequence of partial liver immaturity at birth. Using two-dimensional immuno-electrophoresis we were unable to detect subcarboxylated forms of protein C. However these abnormal forms could be seen in vitamin-K deficiencies of neonates.

Thrombomodulin levels during normal pregnancy, at delivery and in the postpartum: comparison with tissue-type plasminogen activator and plasminogen activator inhibitor-1.

Some studies suggest that soluble thrombomodulin (TM) could be used as a marker of preeclampsia or eclampsia. However little is known about the sequential changes of TM during the course of normal pregnancy. Levels of TM were determined in 100 women with uneventful pregnancies. Samples (n = 394) were divided into five study intervals, three during pregnancy, one at delivery and one three days postpartum. As compared with TM levels (median 34.3 ng/ml, range 17.6-61) of a control group of 60 healthy non-pregnant women, TM levels were shown to increase throughout pregnancy, median (and range) values being respectively 38.5 (17.6-72.7) from 11 to 20 weeks, 45.2 (22.6-75.2) from 21 to 30 weeks and 54.3 (25.1-114.5) ng/ml from 31st week to delivery. One hour after delivery TM levels were still elevated and dropped three days postpartum to 40.5 (20.9-79.4) ng/ml. The increase of TM levels was correlated with those of tissue-type plasminogen activator and plasminogen activator inhibitor-1 antigens. The large overlap in TM levels between the study periods seems to preclude a clinical use of TM based on reference values from a control group. Our data suggest that it would be more appropriate to take into account TM baseline values in a given woman to examine her TM increase during pregnancy.

Vitamin K dependent proteins in fetal hemostasis at mid trimester of pregnancy.

The vitamin K dependent coagulation factor activities were measured in 63 normal human fetuses from 19 to 28 weeks of pregnancy. These activities were included between 9 to 28 percent of normal adult levels. Prothrombin antigen, factor IX antigen and protein C were also measured. There is a good correlation between prothrombin procoagulant activity and antigenicity, suggesting that low level of these vitamin K dependent proteins in fetuses is probably a consequence of liver immaturity.

A cross sectional study of antiphospholipid-protein antibodies in patients with venous thromboembolism.

OBJECTIVE: To look for an association between venous thromboembolism (VTE) and antiphospholipid antibodies (aPL) in patients without Systemic Lupus Erythematosus (SLE) when implementing, beside conventional assays, new tests for aPL screening directed towards purified proteic targets. METHODS: We conducted a cross-sectional, hospital-based study of consecutive unselected outpatients. We compared VTE+ patients to VTE- among 398 consecutive unselected outpatients referred for clinical suspicion of VTE. To detect aPL, the following ELISAs were performed: 1) a conventional standardized ELISA 2) an improved APA assay, 3) an anti-Beta2GPI ELISA, 4) an anti-Annexin V ELISA, 5) an anti-Prothrombin ELISA. We sought an association between VTE and aPL through a quantitative (t-test) and a qualitative comparison (chi-square test, according to the cut-off values set as the 95th percentile of aPL distribution). First we conducted an analysis of all patients. Then we stratified them into 2 subgroups, with or without a wellknown risk factor for VTE (prolonged immobilization >72h, surgery or trauma within the past three months, current malignancy). RESULTS: 61% of patients were classified as VTE-positive. Before stratification, we did not find any significant association between the VTE status and aPL. However, after stratification, in the subgroup without risk factors for VTE, the frequency of positive values as regards the anti Prothrombin antibodies detection was significantly higher in VTE+ patients (p = 0,04). CONCLUSION: The presence of anti Prothrombin antibodies might be an independent risk factor of VTE. However systematic screening for aPL in non SLE patients referred for VTE suspicion at the time of the thrombo-embolic event has little clinical relevance.

Heparin-associated thrombocytopenia: isolation of the antibody and characterization of a multimolecular PF4-heparin complex as the major antigen.

Sera of 34 patients with heparin-associated thrombocytopenia (HAT), giving a positive result in the serotonin release assay (SRA), were assessed in a platelet factor 4 (PF4)/heparin ELISA. Three sera revealing indeterminate results in the SRA and 10 control sera were also investigated. Both tests correlated closely (Kappa 0.742; p = 2.67 x 10(-7)), but one positive serum in the SRA was negative in the pF4/heparin ELISA. We have isolated the HAT antibodies by absorbtion and elution of HAT sera using endothelial cells (HUVEC). Eluates gave similar results as the sera in the PF4/heparin ELISA (Kappa 0.837, p = 9.26 x 10(-9)), and they also correlated very closely with the SRA (Kappa 0.888; p = 8.89 x 10(-10)). This demonstrates that HAT antibodies bind to the same epitope on platelets and on endothelial cells. High heparin concentrations released PF4 in a dose dependent manner from microtiter plates if PF4/heparin, but not if PF4 alone, was covalently linked. Concomitant to the release of PF4, binding of HAT antibodies to PF4/heparin decreased, as indicated by the median optical density (OD) values of OD 0.88 in the presence of buffer compared to OD 0.181 in the presence of 100 IU/ml heparin. The latter values were similar to those obtained when plates were coated with PF4 alone (median OD 0.203). Binding of three eluates was not inhibited by high heparin concentrations and they reacted also with PF4 alone. We conclude that multimolecular PF4/heparin complexes represent the major antigen in HAT. These multimolecular complexes might present several epitopes and form immune complexes after HAT antibody binding which activate platelets via the FcRII. In a few cases, PF4 alone can be recognized by the antibody. However, there is also evidence that other molecules might be involved in some patients.

Diagnostic value of a new sensitive membrane based technique for instantaneous D-dimer evaluation in patients with clinically suspected deep venous thrombosis.

BACKGROUND: Plasma D-Dimer analysis, using ELISA assays, has demonstrated in previous studies a high sensitivity, suggesting its utility in excluding deep venous thrombosis (DVT). AIM: To assess the performance of a new rapid plasma D-Dimer ELISA measurement in suspected DVT patients with recent clinical signs, not exceeding one week. METHODS: A prospective study of patients admitted for a suspected recent DVT. Contrast venography or compression ultrasonography were performed within 24 h of admission. A new membrane based ELISA technique, which uses an immunofiltration and two complementary monoclonal antibodies was tested. Results were expressed as positive or negative. A standard plasma D-Dimer ELISA measurement was also performed. D-Dimer performances were assessed at the end of the study. RESULTS: 265/448 patients had a proven DVT (72 distal, 193 proximal). The sensitivity of the instantaneous method in the diagnosis of overall DVT is 92 +/- 3.4% (95% CI), and specificity is 36.6 +/- 6.9%. Positive predictive value is 67.7 +/- 4.8% and negative predictive value is 76.1 +/- 8.9%. Sensitivity and negative predictive values reach 97.9 and 94.3% in the diagnosis of proximal DVT, but only 76.3 and 79.7% in the diagnosis of distal DVT. Similar results are observed with the standard ELISA method. CONCLUSION: This new rapid plasma D-Dimer measurement appears highly sensitive, and could substitute the older ELISA methods. Both methods provide lower sensitivity in the case of a distal DVT location.

Soluble adhesion molecules and endothelial cell damage in HIV infected patients.

Endothelial damage is present in HIV infection but our understanding of markers and mechanisms is incomplete. We found increased levels of markers of endothelial cell damage such as von Willebrand factor (vWf), soluble thrombomodulin (sTM) and adhesion molecule E-selectin in 90 subjects seropositive for HIV relative to healthy controls. sTM was strongly raised in those patients with the lowest CD4+ cell count (p < 0.001), but levels of vWf increased at each incremental fall in CD4+ cell count and the two indices correlated significantly (r = -0.485, p < 0.001). vWf correlated strongly with levels of the inflammatory cytokines tumor necrosis factor (TNF-alpha) and alpha interferon (IFN-alpha) but sTM correlated only weakly with IFN-alpha. We suggest that increased vWf is largely the result of inflammatory stimulus of the endothelium but that sTM is found only in those patients with more severe disease, and so truly represents endothelial damage.

Antibodies to macromolecular platelet factor 4-heparin complexes in heparin-induced thrombocytopenia: a study of 44 cases.

As heparin-PF4 (H-PF4) complexes are the target for antibodies associated to heparin-induced thrombocytopenia (HIT), an ELISA has been developed and optimised for testing antibodies binding to H-PF4. This test was consistently negative in 50 healthy subjects (A492 < 0.3) and 35 patients with other causes of thrombocytopenia (A492 < 0.5). In contrast, 43 out of 44 HIT patients showed antibodies to H-PF4 (A492 = 1.70 +/- 0.81) including 5 patients with a negative platelet aggregation test. In one patient with HIT, antibodies to H-PF4 were already present at day 7, whereas platelet counts dropped < or = 100 x 10(9)/l only at days 11-12. Surprisingly, among 41 patients under heparin for > 7 days, 5 showed antibodies to H-PF4, without HIT. These findings underline the major interest of this ELISA for the early diagnosis of HIT. We also showed that LMWH as well as other sulphated polysaccharides can bind to HIT antibodies in the presence of PF4 and that their reactivity is dependent on the molecular weight and the sulphation grade. The mechanism for HIT involves platelet PF4 receptors which bind the macromolecular H-PF4 complexes formed in the presence of a well defined heparin/PF4 ratio.

Predictive value of plasma thrombomodulin in preeclampsia and gestational hypertension.

In a prospective longitudinal study, 130 primigravidae at risk for preeclampsia were examined and plasma sampling performed in 45 of them. Plasma thrombomodulin (pTM) was sequentially measured at weeks 12, 24 and 32 of gestation and after delivery in 20 primigravidae who developed either mild preeclampsia (n = 8) or gestational hypertension (n = 12) between weeks 32 and 39 of gestation and in 25 (age-matched) primigravidae who had uneventful pregnancies. pTM elevations were not observed until week 32 in uneventful pregnancies, but were present by week 24 (p = 0.002) in patients who later developed hypertensive complications. A net individual pTM increase > or = 4.2 ng/ml between weeks 12 and 24 (more than 8 times that of normotensive primigravidae) and/or pTM level > or = 47.5 ng/ml at week 32 predicted the development of hypertensive complications with 80% accuracy. Serial pTM determinations can be useful to select pregnancies who may benefit from early pharmacological intervention.