5B9, a monoclonal antiplatelet factor 4/heparin IgG with a human Fc fragment that mimics heparin-induced thrombocytopenia antibodies.

Essentials No humanized monoclonal antibody was available to study heparin-induced thrombocytopenia (HIT). We developed the first anti-platelet factor 4 (PF4)/heparin antibody with a human Fc fragment. This antibody (5B9) fully mimics the effects of human HIT antibodies. 5B9 binds two regions within PF4 that may be critical for the pathogenicity of HIT antibodies. SUMMARY: Background The diagnosis of heparin-induced thrombocytopenia (HIT) is based on clinical and biological criteria, but a standard is lacking for laboratory assays. Moreover, no humanized HIT antibody is available for pathophysiological studies. Objective To characterise 5B9, a chimeric monoclonal antibody, which fully mimics the effects of human HIT antibodies. Methods/Results 5B9, a chimeric anti-platelet factor 4/heparin complexes IgG1 antibody, was obtained after immunizing specific transgenic mice. 5B9 induced heparin FcγRIIA-dependent platelet aggregation and tissue factor mRNA synthesis in monocytes. It also induced significant thrombocytopenia and thrombin generation in mice expressing human PF4 and FcγRIIA receptors. The binding of 5B9 to PF4/H complexes was inhibited by 15 of 25 HIT plasma samples and only three of 25 samples containing non-pathogenic anti-PF4/H antibodies. KKO, a murine IgG2b HIT antibody, also inhibited the binding of 5B9 to PF4/H, suggesting that epitopes recognized by both antibodies are close. A docking analysis based on VH and VL sequences of 5B9 showed that binding of 5B9 Fab to PF4 involved 12 and 12 residues in B and D monomers, respectively, including seven previously identified as critical to the formation of a PF4/KKO complex. Two regions (Asp-7 to Thr-15 and Ala-32 to Thr-38) therefore appeared important for the binding of 5B9 and KKO on PF4 modified by heparin. Conclusions 5B9 is the first anti-PF4/H monoclonal antibody with a human Fc fragment, which induces similar cellular activation as HIT antibodies. Moreover, 5B9 binds epitopes within PF4 that are likely to be critical for the pathogenicity of HIT antibodies.

Agreement between factor XIII activity and antigen assays in measurement of factor XIII: A French multicenter study of 147 human plasma samples.

INTRODUCTION: Factor XIII (FXIII) deficiency is a rare hemorrhagic disorder whose early diagnosis is crucial for appropriate treatment and prophylactic supplementation in cases of severe deficiency. International guidelines recommend a quantitative FXIII activity assay as first-line screening test. FXIII antigen measurement may be performed to establish the subtype of FXIII deficiency (FXIIID) when activity is decreased. METHODS: The aim of this multicenter study was to evaluate the analytical and diagnostic levels of performance of a new latex immunoassay, K-Assay® FXIII reagent from Stago, for first-line measurement of FXIII antigen. Results were compared to those obtained with the Berichrom® FXIII chromogenic assay for measurement of FXIII activity. Of the 147 patient plasma samples, 138 were selected for analysis. RESULTS: The accuracy was very good, with intercenter reproducibility close to 7%. Five groups were defined on FXIII activity level (<5% (n = 5), 5%-30% (n = 23), 30%-60% (n = 17), 60%-120% (n = 69), above 120% (n = 24)), without statistical differences between activity and antigen levels (P value >0.05). Correlation of the K-Assay® with the Berichrom® FXIII activity results was excellent (r = 0.919). Good agreement was established by the Bland and Altman method, with a bias of +9.4% on all samples, and of -1.4% for FXIII levels lower than 30%. One patient with afibrinogenemia showed low levels of Berichrom® FXIII activity but normal antigen level and clot solubility as expected. CONCLUSIONS: The measurement of FXIII antigen using the K-Assay® is a reliable first-line tool for detection of FXIII deficiency when an activity assay is not available.

Bone marrow tryptase as a possible diagnostic criterion for adult systemic mastocytosis.

BACKGROUND: Mastocytosis is difficult to diagnose, especially when systemic mast cell activation symptoms are not present or involve only one extracutaneous organ. OBJECTIVE: The main objective was to evaluate the accuracy of the bone marrow tryptase level in the diagnosis of systemic mastocytosis in patients with a clinical suspicion of mastocytosis. METHODS: We included all adult patients evaluated in our centre between December 2009 and 2013 for suspected mastocytosis as part of a standardized procedure and who had a bone marrow and serum tryptase assay on the same day. The diagnosis of systemic mastocytosis was established on the basis of the World Health Organization criteria as the gold standard. The accuracy of the bone marrow tryptase level in the diagnosis of systemic mastocytosis was assessed by a receiver operating characteristics curve analysis. The different sensitivity and specificity values, corresponding to the set of possible bone marrow tryptase level cut-off values, were estimated with 95% confidence intervals. RESULTS: Seventy-three patients were included. The diagnosis of systemic mastocytosis was established in 43 patients (58.9%). The median bone marrow tryptase level was 423 µg/L [95% CI: 217-868] in the systemic mastocytosis group and 7.5 µg/L [95% CI: 4.6-17.1] in the non-systemic mastocytosis group (P < 0.001). A cut-off value of 50 µg/L for bone marrow tryptase identified systemic mastocytosis with a sensitivity of 93.0% [95% CI: 80.9-98.5%] and a specificity of 90.0% [95% CI: 73.5-97.9%]. CONCLUSION AND CLINICAL RELEVANCE: The bone marrow tryptase level appears to be a valuable diagnostic criterion for confirming systemic mastocytosis. If this diagnosis can reliably be excluded by evaluation of the bone marrow tryptase level, there would be no need to perform a bone marrow biopsy.

Does the presence of von Willebrand factor in FVIII-deficient plasma influences the measurement of FVIII inhibitor titres in haemophilia A patients?

INTRODUCTION: Reliable measurement of FVIII inhibitor is critical in the follow-up of haemophilia A patients. We performed a multicentre study to evaluate whether the presence of von Willebrand factor (VWF) in FVIII-deficient plasma (FVIII-DP) influences FVIII inhibitor titres. METHODS: Six French haematology laboratories participated in this study. Three samples with varying FVIII inhibitor titres (1, 5 and 15 BU/mL) and one sample without any detectable FVIII inhibitor were tested using four different procedures for FVIII inhibitor assay. The Nijmegen method and a modified assay with imidazole were performed using FVIII-DP with and without VWF in the control mixture and as substrate plasma in the FVIII one stage assay (OSA). Each mixture (reference and test) was incubated for two hours at 37 °C with buffered normal pool plasma. RESULTS: Higher inhibitor titres were measured in 5 and 15 BU/mL samples when assays were performed with the Nijmegen method and FVIII-DP without VWF. When samples were diluted in imidazole buffer, similar inhibitor titres, close to expected values, were measured whether VWF was present in the FVIII-DP or not. The data obtained were also more accurate when residual FVIII activity levels between 40% and 60% were used to calculate inhibitor titres, despite a linear type I reaction kinetics. CONCLUSION: These results support the hypothesis that reliable FVIII inhibitor titres can be measured without the use of FVIII-DP containing VWF when an imidazole-modified assay is used.

[Heparin-induced thrombocytopenia: recent data]. / Les thrombocytopénies induites par l'héparine: données récentes.

Despite less frequent, heparin-induced thrombocytopenia (HIT) remains a severe complication of treatment with heparin, and is important to diagnose and manage appropriately. HIT results from an atypical immune response to heparin, with the synthesis of IgG antibodies specific to heparin-modified platelet factor 4 (PF4) which activate platelets, leukocytes and the endothelium. This activation explains that low platelet count is associated with thrombotic events in 50% of patients. The diagnosis of HIT is sometimes evoked because of atypical manifestations (i.e. cutaneous necrosis, amnesia, hypotension or dyspnea following intravenous injection of heparin). Biological assays are always necessary to confirm HIT in case of clinical suspicion, and specific rapid tests are now available for detecting anti-PF4 antibodies. However, their specificity is poor and functional assays such as serotonin release assay or platelet aggregation test are often necessary. Argatroban that is a direct antithrombin drug can be used in patients with severe renal failure and will be preferred to danaparoid sodium in this situation. Fondaparinux is not licensed for treating confirmed HIT and can only be used in case of suspicion. The early detection of HIT is based on the monitoring of platelet count recommended in surgical patients receiving a low molecular weight heparin and in all patients treated with unfractionated heparin.

Psoriasis, cardiovascular events, cancer risk and alcohol use: evidence-based recommendations based on systematic review and expert opinion.

The relationship between psoriasis, chronic inflammation, cardiovascular risk and risk of cancer has long been debated. In addition, it has been suggested that alcohol consumption may be a risk factor for psoriasis onset and severity. The aim of this study was to develop evidence-based recommendations on the risk of comorbidities and its management for daily clinical use, focusing on cardiovascular risk, risk of cancer and alcohol use in psoriasis. A scientific committee identified and selected through the Delphi method clinically relevant questions about cardiovascular risk, risk of cancer and alcohol use in psoriasis. To address these questions, a systematic literature search was performed in Medline, Embase and the Cochrane Library databases. Systematic literature reviews including meta-analysis whenever possible were performed. Subsequently, an Expert board meeting involving 39 dermatologists took place to analyse the evidence and to elaborate recommendations on the selected questions. Recommendations were graded according to the Oxford level of evidence grading system. The degree of agreement of these recommendations was assessed on a 10-point scale, as well as their potential impact on daily clinical practice. A total of 3242 articles were identified through the systematic literature searches, among which 110 were included in the systematic reviews. Overall, 12 recommendations were elaborated regarding comorbidities management in psoriasis patients. A moderate increased risk of cardiovascular diseases (CVD), mainly myocardial infarction (MI) [meta-analysis of cohort studies: OR = 1.25 (95% CI 1.03-1.52) and of cross-sectional studies: OR = 1.57 (95% CI 1.08-2.27)], and coronary artery disease (CAD) [meta-analysis of cross-sectional: OR = 1.19 (95% CI 1.14-1.24), of cohort studies: OR = 1.20 (95% CI 1.13-1.27) and of case-control studies: OR = 1.84 (95% CI 1.09-3.09)] was acknowledged. This increased cardiovascular risk requires appropriate prevention measures. There was a lack of substantial evidence that conventional systemic treatment has any effect on cardiovascular risk although methotrexate might be cardioprotective. An increased risk of solid cancer potentially associated with smoking and alcohol use was identified. The role of systemic treatment on cancer risk could not be assessed thoroughly due to limited long-term follow-up data. A higher risk of non-melanoma skin cancers especially squamous cell carcinoma was shown, mainly due to previous exposure to oral 8-methoxypsoralen-ultraviolet-A (PUVA), ciclosporin and possibly methotrexate. No firm conclusion could be drawn regarding alcohol and psoriasis due to high variability in alcohol usage assessment in studies. Clinical experience suggests higher alcohol consumption among psoriasis patients compared to the general population. The mean expert participants' level of agreement on these recommendations varied from 6.8 to 9.4. These 12 recommendations are evidence based and supported by a panel of expert dermatologists. The next step is now to disseminate these recommendations to dermatologists who did not participate in the Expert board meeting and to assess their opinion about the recommendations.

Cardiovascular morbidity and mortality in psoriasis and psoriatic arthritis: a systematic literature review.

UNLABELLED: Previous epidemiological studies have demonstrated a high prevalence of cardiovascular (CV) risk factors in psoriasis patients, including metabolic syndrome, cigarette smoking, obesity, hypertension, diabetes mellitus, insulin resistance and dyslipidaemia. An increase in CV morbidity and mortality attributable to psoriasis is still under question. PRIMARY OBJECTIVE: to assess CV morbidity and mortality in psoriasis and psoriatic arthritis (PsA) including stroke, coronary artery disease, myocardial infarction (MI) and peripheral artery disease. SECONDARY OBJECTIVES: to assess if psoriasis per se is an independent CV risk factor and if psoriasis severity is a predictor of CV risk. We also evaluated the effect of conventional systemic treatments for psoriasis on CV mortality. A systematic literature search was carried out from 1980 to December 2011, in the Embase, Medline and Cochrane Library databases, in English and French using a combination of keywords including (Psoriasis) OR (Psoriatic arthritis) AND (Myocardial infarction) OR (Coronaropathy) OR (Stroke) OR (Cardiovascular) AND (Methotrexate) AND (Ciclosporin) AND (Retinoids). Of the 929 identified references, 33 observational studies evaluating the rates of cardiovascular events (CVE) in patients with psoriasis and PsA compared with controls were selected. Meta-analysis of both cohort and cross-sectional studies showed an increased risk of MI with Odds Ratio (OR) of 1.25 (95% CI 1.03-1.52) and 1.57 (95% CI 1.08-2.27) in psoriasis and PsA, respectively, compared with the general population. The risk of MI was more pronounced for patients having severe psoriasis and for patients with psoriasis of early onset. It remained significantly elevated after controlling for major CV risk factors. The meta-analysis identified a small, but significant association between psoriasis, PsA and coronary artery disease with an OR between 1.19 (95% CI 1.14-1.24) for cross-sectional studies, 1.20 (95% CI 1.13-1.27) for cohort studies and 1.84 (95% CI 1.09-3.09) for case-control studies. The risk of coronary artery disease seemed to be more pronounced in patients with severe psoriasis and in patients with psoriasis of early onset. The meta-analysis assessing the risk of stroke gave inconclusive results: analysis of cross-sectional studies suggested that psoriasis patients had a slightly higher risk of stroke with an OR of 1.14 (95% CI 1.08-1.99), whereas the meta-analysis of cohort studies failed to show an association. There was also an increased risk of peripheral artery disease in psoriasis. No significant increased risk of CV mortality could be shown for both psoriasis and PsA patients. The use of methotrexate was associated with a reduced incidence of cardiovascular disease in two studies. The use of etretinate was associated with a reduction of CV mortality in one study. Potential selection bias such as the 'healthy user effect' prevents from drawing definite conclusions. There may be a small, but significant increased risk of CVE, but not of CV mortality in psoriasis and PsA patients. The psoriasis attributable risk remains difficult to assess due to confounding factors. The moderate quality of CV risk factors reporting in studies should be acknowledged. In addition, heterogeneity in study design, outcome definition and assessment represent major limitations. Nevertheless, screening and management of CV risk factors are important in psoriasis.

Alcohol consumption and psoriasis: a systematic literature review.

The association between alcohol consumption and psoriasis has been frequently discussed since the 1980s, but no systematic review has been elaborated on the subject so far. The aim of this systematic literature review was to assess whether alcohol consumption is more prevalent in psoriasis patients than in the general population and whether alcohol consumption is a risk factor of psoriasis. A systematic literature search was carried out in the Medline, Embase and Cochrane databases using the keywords 'psoriasis' AND 'alcohol drinking' OR 'alcohol-related disorders'. The search was then enlarged with the keywords 'psoriasis' AND 'risk factor' OR 'comorbidity'. Altogether 911 references in English and French were found. Out of these, 837 articles were excluded by reading the abstract and 46 by reading the article. A total of 28 articles were selected. Alcohol consumption in psoriasis patients versus the general population: 23 studies were selected; 18 concluded that alcohol consumption was more prevalent in psoriasis patients, and 5 did not. Three studies compared the prevalence of excessive drinking using a questionnaire on alcohol dependence (CAGE or Self-administered alcohol screening test (SAAST)) or with quantitative criteria for excessive drinking. In these studies, excessive drinking was more prevalent among psoriasis patients than in the general population. Other articles studied the quantity and type of alcohol consumed. In 11 studies, psoriasis patients consumed more alcohol than the controls. Four other studies showed excessive alcohol consumption in psoriasis patients without control group comparison. Conversely, five studies identified no difference in alcohol consumption between psoriasis patients and the general population. The heterogeneity in the measurement of alcohol consumption did not allow performing meta-analysis. Alcohol as a risk factor for psoriasis: only five studies were selected. In four of these studies alcohol was found to be a risk factor for psoriasis. Alcohol consumption seems to be greater in psoriasis patients than in the general population. However, there is not enough evidence to establish whether alcohol consumption is indeed a risk factor for psoriasis.

Risk of cancer in psoriasis: a systematic review and meta-analysis of epidemiological studies.

The relationship between psoriasis and increased cancer risk is debated. The aim of this study was to evaluate if there is an increase in the background risk of cancer in psoriasis patients compared with the general population. A systematic literature search was performed on PubMed, Embase and Cochrane databases, using the keywords 'Psoriasis [Majr] AND Neoplasms', from 1980 to January 2012. Meta-analysis was performed based on observational studies showing consistency in cancer risk assessment methods. Of the 1080 articles retrieved, 37 references were selected. There may be an increased risk of some solid cancers in psoriasis: respiratory tract cancer [standardized incidence ratio (SIR) = 1.52, 95% confidence interval (CI) 1.35-1.71], upper aerodigestive tract cancer (SIR = 3.05, 95% CI 1.74-5.32), urinary tract cancer (SIR = 1.31, 95% CI 1.11-1.55) and liver cancer (SIR = 1.90, 95% CI 1.48-2.44). The risk of non-Hodgkin lymphoma appears slightly increased in psoriasis (SIR = 1.40, 95% CI 1.06-1.86). Psoriasis patients have an increased risk of squamous cell carcinoma (SIR = 5.3, 95% CI 2.63-10.71) and basal cell carcinoma (SIR = 2.00, 95% CI 1.83-2.20), whereas the risk of melanoma is not increased. There was a large heterogeneity in studies assessing cancer risk in psoriasis preventing from including all studies in meta-analysis. This systematic literature review shows a small increased risk of some solid cancers in psoriasis, especially those linked to alcohol drinking and cigarette smoking. A higher risk of non-melanoma skin cancers, especially squamous cell carcinoma, is shown, mainly due to previous exposure to 8-methoxypsoralen-ultraviolet-A (PUVA), ciclosporin and possibly methotrexate.

Binding of heparin-dependent antibodies to PF4 modified by enoxaparin oligosaccharides: evaluation by surface plasmon resonance and serotonin release assay.

BACKGROUND: The minimal structural requirements of low-molecular-weight heparins that determine the risk of developing heparin-induced thrombocytopenia (HIT) are not fully defined. OBJECTIVES: The ability of enoxaparin-derived oligosaccharides (OS) to induce platelet activation and exposure of platelet-factor 4 (PF4) epitopes recognized by antibodies developed in HIT was studied by surface plasmon resonance (SPR) and serotonin release assay. RESULTS: Decasaccharides with ≥ 11 sulfate groups induced platelet activation in the presence of plasma from patients with confirmed HIT. Serotonin release of > 80% without full inhibition at 100 µg mL(-1) was achieved with decasaccharides containing 14 or 15 sulfate groups, 2 dodecasaccharides and 2 tetradecasaccharides. An SPR method was developed using purified PF4 immobilized on carboxymethylated dextran. Antibodies from all HIT samples bound to PF4/heparin in SPR assays with resonance units (RU) ratio of 109-173 with HIT plasma vs. 88-93 with control plasma. RU ratios > 100 were measured when PF4 was pre-incubated with OS with ≥ 10 saccharide units and one octasaccharide containing 10 sulfate groups. RU ratios > 140, similar to those measured when PF4 was pre-incubated with unfractionated heparin or enoxaparin, were obtained with purified dodeca- and tetradecasaccharides. RU values strongly correlated with the number of sulfate groups in the decasaccharides tested (r = 0.93, P = 0.02). CONCLUSIONS: LMWHs with fragments > 10 saccharides and a large number of sulfate groups are more likely to be associated with a higher risk of HIT. These structure-activity relationships were independent of the ability of the OS to bind antithrombin.

Are we giving patients enough information on how to use topical treatments? Analysis of 767 prescriptions in psoriasis.

BACKGROUND: Unclear instructions probably contribute to the suboptimal efficacy and adherence to topical agents in psoriasis. OBJECTIVES: To analyse the quality of prescriptions for topical therapy in psoriasis and to determine factors associated with high-quality prescription writing. METHODS: We made a systematic analysis of 767 topical prescriptions written by dermatologists and general practitioners (GPs). The following parameters were recorded: writing mode (electronic vs. hand written), indication of formulation, frequency of administration, duration of treatment, indication of areas to be treated, and indication of amount of product to be used. We considered prescriptions of high quality to be those including at least four of the five prospectively defined quality parameters. RESULTS: Only 35·7% of prescriptions fulfilled the definition of a high-quality prescription. Quality of prescription writing was significantly influenced by two factors: electronic writing [odds ratio (OR) 3·04, 95% confidence interval (CI) 2·2-4·21; P < 10(-4) ] and specialty of the prescriber, dermatologists writing higher quality prescriptions compared with GPs (OR 1·61, 95% CI 1·54-2·14; P < 10(-4) ). CONCLUSIONS: Almost two-thirds of topical prescriptions are not adequately written and do not include the required information to help patients manage their topical treatment in psoriasis correctly. The quality of topical prescriptions could be improved by making the use of electronic prescriptions widespread and by the development of aids for easy evaluation of the right amount of topical treatment to be applied according to body surface area involved.

The use of the new ReFacto AF Laboratory Standard allows reliable measurement of FVIII:C levels in ReFacto AF mock plasma samples by a one-stage clotting assay.

Factor VIII coagulant (FVIII:C) levels measured in patients receiving ReFacto® (B-domain-deleted recombinant FVIII) using chromogenic substrate assay (CSA) and one-stage clotting assay (OSA) have frequently shown discrepancies, and the use of the ReFacto Laboratory Standard (RLS) has therefore been recommended to minimize these differences. The potency of ReFacto AF®, the albumin-free successor of ReFacto®, is determined using CSA for the titration of vials, and a new standard (RLS-AF) was developed to measure its biological efficacy using OSA. This multicentre study therefore evaluated the efficacy of this new RLS in minimizing differences between OSA and CSA when measuring FVIII:C levels in plasma. Mock plasma samples were prepared by diluting ReFacto AF® in FVIII-deficient plasma to obtain four concentrations ranging from 15 to 90 IU dL⁻¹ . FVIII:C levels were then measured in six laboratories on four separate days using three different procedures, i.e. OSA with a plasma standard (PS) as reference, OSA with RLS-AF and CSA with PS. The inter-centre standard deviation ranged from 1.4 to 5.5 IU dL⁻¹. However, FVIII:C levels measured with OSA were closer to the expected values when RLS-AF was used. In addition, the uncertainty of measurement, reflecting the inter-method discrepancy was greatly reduced when RLS-AF was employed in OSA (15%) in place of PS (33%). This study demonstrates that the OSA performed with RLS-AF to establish calibration curves provides a valuable alternative to CSA to measure FVIII:C in ReFacto-AF-treated patients.

[Tranexamic acid reduces haematomas but not pain after total knee arthroplasty]. / L'acide tranexamique diminue les hématomes mais pas les douleurs après prothèse totale de genou.

AIM: Tranexamic acid (TxA) reduces total blood losses (TBL) and allogenic transfusion (TH) after total knee arthroplasty (TKA). TBL can be external (surgical field, drains), or hidden (haematomas). Haematomas induce pain and limit postoperative rehabilitation. The aim of the study was to evaluate if TxA reduces haematomas and pain after TKA. STUDY DESIGN: Prospective non-randomized study. METHOD: After ethical committee approvement and written informed consent, the patients planned for a primary TKA were included (control group followed by a TxA group, 15 mg/kg before incision and at skin closure). General anaesthesia and analgesia were standardized (sciatic block, continuous femoral block, ketamine, ketoprofene, paracetamol, PCA with morphine). Volume of haematomas=TBL (calculated based on haemograms performed the day before surgery, and at postoperative day 5, and on transfusions)-measured external bleeding. Patients were followed up for 8 days, and at postoperative day 180 (by phone). Fifty patients per group allowed the detection of a 50% morphine sparing at day 8 (α=0.05 and ß=0.2), and a 25% reduction of haematoma volumes at day 5. RESULTS: Perioperative data, pain scores and functional parameters (until day 180) were not different between control group patients (n=52) and TxA group patients (n=55): morphine consumption at day 8 was respectively 35 ± 32 and 42 ± 38 mg (P=0.29). Yet, TxA reduced hematoma volumes (526 ± 202 versus 337 ± 165 mL of red blood cells, P<0.0001) and clinically apparent hematomas. Morphine consumptions at day 8 and haematoma volumes were not correlated. CONCLUSION: After TKA, TxA reduces the volume of hematomas, without any improvement in analgesia and rehabilitation until the sixth postoperative month.

Heparin-induced thrombocytopenia: a frequent complication after cardiac surgery.

Thrombocytopenia is a common problem in cardiovascular patients, and heparin-induced thrombocytopenia (HIT) is therefore frequently suspected. Unfractionated heparin during cardiopulmonary bypass is particularly immunogenic as 25% to 50% post-cardiac surgery patients develop heparin-dependent antibodies but only 1 to 3% will develop HIT. These antibodies recognize a 'self protein', platelet factor 4 (PF4), bound to heparin. Antibodies associated with a high risk of HIT are mainly IgG1 which strongly activate platelets and coagulation, thereby causing thrombocytopenia and thrombosis. A biphasic evolution of platelet count with a secondary decrease after a previous increase following CPB or non-recovery of thrombocytopenia within 6 days post-operatively always requires screening for HIT antibodies. Both functional (platelet activation tests) and immunologic assays (antigen assays) are necessary in every patient to establish the diagnosis of HIT. When the clinical probability of HIT is high, the first requirement is to discontinue heparin, without waiting for results of laboratory investigations. An alternative anticoagulant such as danaparoid sodium (Orgaran) or lepirudin (Refludan) must then be administered since heparin withdrawal alone is insufficient to control the prothrombotic state associated with HIT. The risk of HIT will probably soon decrease due to the wider use of fondaparinux, which does not interact in vitro with PF4, but it could remain significant in patients undergoing cardiac surgery with CPB.

Prospective evaluation of the '4Ts' score and particle gel immunoassay specific to heparin/PF4 for the diagnosis of heparin-induced thrombocytopenia.

BACKGROUND: Heparin-induced thrombocytopenia (HIT) is a severe disease that is often difficult to diagnose. A clinical scoring system, the '4Ts' score, has been proposed to estimate its probability before laboratory testing, and a particle gel immunoassay (H/PF4 PaGIA) has also been developed for rapid detection of HIT antibodies. AIM: To evaluate the performance of both methods when HIT is suspected clinically. METHODS: Two hundred thirteen consecutive patients were included in four centers. The probability of HIT was evaluated using the 4Ts score blind to antibody test results. HIT was confirmed only when the serotonin release assay (SRA) was positive. RESULTS: The risk of HIT was evaluated by the 4Ts score as low (LowR), intermediate (IR) or high (HR) in 34.7%, 60.6% and 4.7% of patients, respectively. The negative predictive value (NPV) of the 4Ts score was 100%, as the SRA was negative in all LowR patients. PaGIA was negative in 176 patients without HIT (99.4%, NPV) and the negative likelihood ratio (LR-) was 0.05. PaGIA was positive in 37 patients, including 21 with HIT (positive predictive value = 56.8%), with a positive LR of 11.4. A negative PaGIA result decreased the probability of HIT in IR patients from 10.9% before assay to 0.6%, whereas a positive result did not substantially increase the likelihood for HIT. CONCLUSION: The use of the 4Ts score with PaGIA appears to be a reliable strategy to rule out HIT.