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Background Atypical hemolytic uremic syndrome (aHUS), a severe thrombotic microangiopathy, is often related to complement dysregulation, but the pathomechanisms remain unknown in at least 30% of patients. Researchers have described autoantibodies to complement factor H of the IgG class in 10% of patients with aHUS but have not reported anti-factor H autoantibodies of the IgM class. Methods In 186 patients with thrombotic microangiopathy clinically presented as aHUS, we searched for anti-factor H autoantibodies of the IgM class and those of the IgG and IgA classes. We used immunochromatography to purify anti-factor H IgM autoantibodies and immunoenzymatic methods and a competition assay with mapping mAbs to characterize interaction with the target protein. Results We detected anti-factor H autoantibodies of the IgM class in seven of 186 (3.8%) patients with thrombotic microangiopathy presented as aHUS. No association was observed between anti-factor H IgM and homozygous deletions involving CFHR3-CFHR1. A significantly higher proportion of patients with bone marrow transplant-related thrombotic microangiopathy had anti-factor H IgM autoantibodies versus other patients with aHUS: three of 20 (15%) versus four of 166 (2.4%), respectively. The identified IgM autoantibodies recognize the SCR domain 19 of factor H molecule in all patients and interact with the factor H molecule, inhibiting its binding to C3b. Conclusions Detectable autoantibodies to factor H of the IgM class may be present in patients with aHUS, and their frequency is six-fold higher in thrombotic microangiopathy forms associated with bone marrow transplant. The autoantibody interaction with factor H's active site may support an autoimmune mechanism in some cases previously considered to be of unknown origin.

The pathophysiology of the severe complications of COVID-19 is still unclear. We report preliminary data providing evidence of complement activation in patients with COVID-19 with different degrees of respiratory failure.

Atypical hemolytic uremic syndrome (aHUS) is characterized by platelet consumption, hemolysis, and renal injury. Eculizumab, a humanized antibody that blocks complement activity, has been successfully used in aHUS, but the best treatment schedule has not yet been clearly defined.Herein we report our experience with eculizumab maintenance treatment, in which the interval between subsequent doses was adjusted based on classical complement pathway (CCP) activity, targeted to 30% for the prevention of relapses. Trough circulating levels of free eculizumab were determined by an immunoenzymatic method. Genetic and serologic characteristics of the patients were also assessed.We report on 38 patients with aHUS with a median age of 25.0 years (range 0.5-60.0 years) treated with eculizumab. Once stable disease remission was obtained, the interval between eculizumab doses was extended based on target CCP activity. With this approach, presently, 22 patients regularly receive eculizumab infusion every 28 days and 16 receive it every 21. During a median observation period of 32.3 months (range 4.0-92.4 months) and a cumulative period of 1295 months, no patient relapsed. An inverse correlation between CCP activity and eculizumab circulating levels was present (r = - 0.690, p = 0.0001), with CCP activity being inhibited as long as free eculizumab was measurable in serum.In patients with aHUS on eculizumab maintenance treatment, complement activity measurement can be used as a proxy for circulating levels of the drug. Monitoring complement activity allows for safe tailoring of the frequency of eculizumab administration, thus avoiding excessive drug exposure while keeping the disease in remission.

Background Genetic variation at a multigene cluster at chromosome 3p21.31 and the ABO blood group have been associated with the risk of developing severe COVID-19, but the mechanism remains unclear. Complement activation has been associated with COVID-19 severity. Objective The aim of this study was to examine whether chromosome 3p21.31 and the ABO variants are linked to the activation of the complement cascade in COVID-19 patients. Methods We considered 72 unrelated European hospitalized patients with genetic data and evaluation of circulating C5a and soluble terminal complement complex C5b-9 (SC5b-9). Twenty-six (36.1%) patients carried the rs11385942 G>GA variant and 44 (66.1%) non-O blood group associated with increased risk of severe COVID-19. Results C5a and SC5-b9 plasma levels were higher in rs11385949 GA carriers than in non-carriers (P = 0.041 and P = 0.012, respectively), while C5a levels were higher in non-O group than in O group patients (P = 0.019). The association between rs11385949 and SC5b-9 remained significant after adjustment for ABO and disease severity (P = 0.004) and further correction for C5a (P = 0.018). There was a direct relationship between upper airways viral load and SC5b-9 in carriers of the rs11385949 risk allele (P = 0.032), which was not observed in non-carriers. Conclusions The rs11385949 G>GA variant, tagging the chromosome 3 gene cluster variation and predisposing to severe COVID-19, is associated with enhanced complement activation, both with C5a and terminal complement complex, while non-O blood group with C5a levels. These findings provide a link between genetic susceptibility to more severe COVID-19 and complement activation., Highlights • The rs11385942 G>GA variant and ABO blood group are linked to severe COVID-19. • Complement activation parallels severity and disease activity in COVID-19 patients. • In COVID-19, we found that rs11385949 G>GA predispose to complement activation. • Non-O blood group is also associated with complement activation in COVID-19 patients.

Extremely rare reactions characterized by thrombosis and thrombocytopenia have been described in subjects that received ChAdOx1 nCoV-19 vaccination 5-16 days earlier. Although patients with vaccine-induced thrombotic thrombocytopenia (VITT) have high levels of antibodies to platelet factor 4 (PF4)-polyanion complexes, the exact mechanism of the development of thrombosis is still unknown. Here we reported serum studies as well as proteomics and genomics analyses demonstrating a massive complement activation potentially linked to the presence of anti-PF4 antibodies in a patient with severe VITT. At admission, complement activity of the classical and lectin pathways were absent (0% for both) with normal levels of the alternative pathway (73%) in association with elevated levels of the complement activation marker sC5b-9 (630 ng/mL [n.v. 139-462 ng/mL]) and anti-PF4 IgG (1.918 OD [n.v. 0.136-0.300 OD]). The immunoblotting analysis of C2 showed the complete disappearance of its normal band at 110 kDa. Intravenous immunoglobulin treatment allowed to recover complement activity of the classical pathway (91%) and lectin pathway (115%), to reduce levels of sC5b-9 (135 ng/mL) and anti-PF4 IgG (0.681 OD) and to normalize the C2 pattern at immunoblotting. Proteomics and genomics analyses in addition to serum studies showed that the absence of complement activity during VITT was not linked to alterations of the C2 gene but rather to a strong complement activation leading to C2 consumption. Our data in a single patient suggest monitoring complement parameters in other VITT patients considering also the possibility to target complement activation with specific drugs.

Patients with atypical hemolytic uremic syndrome (aHUS) have long been considered ineligible for kidney transplantation (KTx) in several centers due to the high risk of disease recurrence, graft loss and life-threatening complications. The availability of Eculizumab (ECU) has now overcome this problem. However, the best approach towards timing, maintenance schedule, the possibility of discontinuation and patient monitoring has not yet been clearly established. This is a single center case series presenting our experience with KTx in aHUS. This study included 26 patients (16 females) with a diagnosis of aHUS, who spent a median of 5.5 years on kidney replacement therapy before undergoing KTx. We compared the aHUS relapse rate in three groups of patients who underwent KTx: patients who received no prophylaxis, patients who underwent plasma exchange, those who received Eculizumab prophylaxis. Complement factor H-related disease was by far the most frequent etiology (n = 19 patients). Untreated patients and patients undergoing pre-KTx plasma exchange prophylaxis had a relapse rate of 0.81 (CI 0.30–1.76) and 3.1 (CI 0.64–9.16) events per 10 years cumulative observation, respectively, as opposed to 0 events among patients receiving Eculizumab prophylaxis. The time between Eculizumab doses was tailored based on classic complement pathway activity (target to

Background Animal models and few clinical reports suggest the involvement of the complement system in the onset of severe manifestations of coronavirus disease-2019 (COVID-19). However, complement contribution to endotheliopathy and hypercoagulability has not been elucidated yet. Objective To evaluate the association among complement activation, endothelial damage and disease severity or activity in COVID-19 patients. Methods In this single-centre cohort study, 148 patients with COVID-19 of different severity were evaluated upon hospital admission and 30 days later. Markers of complement activation (SC5b-9 and C5a) and endothelial perturbation (von Willebrand factor [vWF], tissue-type plasminogen activator [t-PA], plasminogen activator inhibitor-1 [PAI-1], soluble thrombomodulin [sTM], and soluble endothelial selectin [sE-selectin]) were measured in plasma. Results The patients had high plasma levels of SC5b-9 and C5a (p = 0.0001 for both) and vWF, t-PA and PAI-1 (p = 0.0001 for all). Their SC5b-9 levels correlated with those of vWF (r = 0.517, p = 0.0001) and paralleled disease severity (severe vs mild p = 0.0001, severe vs moderate p = 0.026 and moderate vs mild p = 0.001). The levels of sE-selectin were significantly increased only in the patients with severe disease. After 30 days, plasma SC5b-9, C5a and vWF levels had significantly decreased (p = 0.0001 for all), and 43% of the evaluated patients had normal levels. Conclusions Complement activation is boosted during the progression of COVID-19 and dampened during remission, thus indicating its role in the pathophysiology of the disease. The association between complement activation and the biomarkers of endothelial damage suggests that complement may contribute to tissue injury and could be the target of specific therapy.

Genetic variation at a multigene cluster at chromosome 3p21.31 and the ABO blood group have been associated with the risk of developing severe COVID-19, but the mechanism remains unclear. Complement activation has been associated with COVID-19 severity.The aim of this study was to examine whether chromosome 3p21.31 and the ABO variants are linked to the activation of the complement cascade in COVID-19 patients.We considered 72 unrelated European hospitalized patients with genetic data and evaluation of circulating C5a and soluble terminal complement complex C5b-9 (SC5b-9). Twenty-six (36.1%) patients carried the rs11385942 GGA variant and 44 (66.1%) non-O blood group associated with increased risk of severe COVID-19.C5a and SC5-b9 plasma levels were higher in rs11385949 GA carriers than in non-carriers (P = 0.041 and P = 0.012, respectively), while C5a levels were higher in non-O group than in O group patients (P = 0.019). The association between rs11385949 and SC5b-9 remained significant after adjustment for ABO and disease severity (P = 0.004) and further correction for C5a (P = 0.018). There was a direct relationship between upper airways viral load and SC5b-9 in carriers of the rs11385949 risk allele (P = 0.032), which was not observed in non-carriers.The rs11385949 GGA variant, tagging the chromosome 3 gene cluster variation and predisposing to severe COVID-19, is associated with enhanced complement activation, both with C5a and terminal complement complex, while non-O blood group with C5a levels. These findings provide a link between genetic susceptibility to more severe COVID-19 and complement activation.

Background: Thrombolysis is an effective treatment strategy for prosthetic valve thrombosis (PVT). Recombinant tissue-type plasminogen activator (rt-PA) is widely used as a thrombolytic agent. Infusion of rt-PA may trigger the production of anti–tissue plasminogen activator (tPA) antibodies (ATAs). We aimed to evaluate the possible relationship between ATA levels and PVT formation, and the role of baseline ATA levels on outcomes of thrombolytic therapy in patients with PVT. Methods: This prospective, single-center cohort study included 28 patients with PVT undergoing thrombolysis and 31 controls with normal prostheses. Plasma samples were collected from patients with PVT at baseline and at 15th, 30th, 90th, and 180th days after thrombolysis and from controls at baseline only. The ATA levels were assessed in human plasma by an enzyme-linked immunosorbent assay. Results: Baseline ATA-immunoglobulin (Ig) G and IgM were significantly higher in patients with PVT than in controls. The levels of IgM and IgG peaked at 15th and 30th days after rt-PA infusion, respectively. Subtherapeutic international normalized ratio and baseline ATA-IgM were independent predictors of PVT. Thrombolysis failed in 6 patients (21%) in whom baseline IgM levels were significantly higher than successfully lysed patients. Rethrombosis occurred in 9 patients (32%) in whom baseline IgG levels were significantly higher than those without rethrombosis. There was a moderate positive correlation between baseline and 15th-day IgM levels and the dose of rt-PA needed for successful lysis. Conclusion: The ATA levels tended to be higher in patients with PVT at the time of initial diagnosis compared to controls without PVT. In addition, such patients with PVT and high ATA levels may be at high risk for failed thrombolysis or rethrombosis.

Background Raynaud9s phenomenon (RP) can be the first manifestation of systemic sclerosis (SSc) or other connective tissue diseases (CTDs), often preceding an overt disease by years. It is not known if markers of endothelial damage are detectable in those RP patients who subsequently develop a CTD. Objectives We studied RP patients at their first evaluation to correlate the levels of endothelial markers with the subsequent development of an overt disease 36 months later. Methods Eighty-two patients with RP at their first evaluation were recruited. We measured plasma levels of tissue-type plasminogen activator (t-PA) and von Willebrand factor (vWF), two markers of endothelial damage, and interleukin-6 (IL-6), a pro-inflammatory cytokine. Thirty healthy subjects served as healthy controls. Results At baseline, 67 patients showed capillaroscopic normal pattern and 15 patients, of which 11 were very early SSc, had scleroderma pattern. Plasma levels of t-PA, vWF and IL-6 were higher in patients with capillaroscopic normal pattern (p=0.0001) than in normal controls and even much higher in patients with scleroderma pattern (p=0.0001). In patients with capillaroscopic normal pattern and RP of recent onset ( Conclusions Our findings indicate that markers of endothelial damage are elevated in RP patients who subsequently develop SSc or other CTDs, even in the absence of capillaroscopic abnormalities. Disclosure of Interest None declared

Atypical hemolytic uremic syndrome (aHUS) is a thrombotic microangiopathy (TMA) characterized by platelet consumption, hemolysis, and organ damage. Eculizumab (ECU), a humanized antibody that blocks complement activity, has been successfully used in aHUS, but the best treatment schedule is not yet clear. Here, we report our experience with ECU maintenance treatment and the interval between subsequent doses being extended based on global classical complement pathway (CCP) activity aimed at

Background: Cl-inhibitor (C1-INH) deficiency leads to recurrent attacks of mucocutaneous edema and may be inherited (hereditary angioedema [HAE]) or acquired (acquired angioedema [AAE]), which have the same clinical picture characterized by angioedema involving the skin, gastrointestinal tract, and larynx. Although cutaneous swelling is evident, abdominal angioedema is still a diagnostic challenge and attacks can mimic surgical emergencies. There is currently no laboratory marker for identifying angioedema attacks. Objective: As coagulation and fibrinolysis are activated during angioedema attacks, we assessed if plasma measurements of prothrombin fragment F1 + 2 (marker of thrombin generation) and D-dimer (marker of fibrin degradation) can be useful for the diagnosis of angioedema because of C1-INH deficiency, especially in case of hidden locations as abdominal attacks. Methods: In addition to complement, we measured plasma levels of F1 + 2 and D-dimer in 28 patients with C1-INH deficiency during acute attacks and remission, 35 patients without C1-INH deficiency during abdominal colics, and 20 healthy subjects. Results: Plasma F1 + 2 levels were higher in patients with C1-INH deficiency during remission than in healthy controls (P = 0.001), and further increased during cutaneous and abdominal attacks (P = 0.0001); patients without C1-INH deficiency had normal F1 + 2 levels during abdominal colics. Plasma D-dimer levels were higher in patients with C1-INH deficiency during remission than in controls (P = 0.012) and increased during angioedema attacks, reaching higher levels than in patients without C1-INH deficiency during colics (P = 0.002). Conclusions: During acute angioedema attacks, patients with C1-INH deficiency have high prothrombin fragment F1 + 2 and D-dimer levels, the measurement of which may have an important diagnostic value.

Objective Increased cardiovascular (CV) risk is a rheumatoid arthritis (RA) hallmark and it has been mainly related to chronic systemic inflammation. Since inflammation is linked to coagulation perturbation, both may play a role in increasing CV risk. Treatment with tumor necrosis factor (TNF)-α blocking agents is effective in RA and reduces local and systemic inflammation but there is little information on its effect on coagulation. We therefore investigated inflammation and coagulation plasma biomarkers before and after infliximab treatment in RA patients. Methods We studied 20 patients with active RA and 40 healthy controls. Patients were treated with: a stable dose of methotrexate (10 mg/week), and infliximab (3 mg/kg) at weeks 0, 2, 6 and 14. At baseline and week 14, we determined: disease activity score (DAS-28), visual analogue scale pain, erythrocyte sedimentation rate (ESR), and plasma levels of C-reactive protein (CRP), TNF-α, interleukin (IL)-6, prothrombin fragment 1 + 2 (F1 + 2) and D-dimer. The same inflammation and coagulation parameters were evaluated 1 h after infliximab infusion in 10 patients. Results At baseline, ESR, CRP, TNF-α, IL-6, F1 + 2 and D-dimer levels were significantly higher in RA patients than in controls (P = 0.0001). After 14 weeks of infliximab treatment, there was a significant clinical improvement and ESR and CRP, IL-6, F1 + 2 and D-dimer level decrease (P = 0.001–P = 0.008). The levels of TNF-α, IL-6, F1 + 2 and D-dimer significantly decreased 1 h after infliximab infusion (P = 0.005). Conclusions Infliximab decreases inflammation and coagulation biomarkers in RA patients. Such a combined effect may be pivotal in reducing the whole thrombotic risk in these patients.

In patients with chronic urticaria (CU), plasma shows signs of thrombin generation and autologous plasma skin tests score positive in as many as 95% of cases.To evaluate the initiators of blood coagulation that lead to thrombin generation and fibrinolysis in CU.Activated factor VII, activated factor XII, fragment F(1+2), and D-dimer plasma levels were measured in 37 patients with CU and 37 controls. Skin specimens from 10 patients with CU and 10 controls were tested for tissue factor immunohistochemically.Mean F(1+2) levels were higher in patients than controls (2.54 [SD 2.57] nmol/L vs 0.87 [0.26] nmol/L; P.001); disease activity was moderate or severe in 9 of 11 (82%) and 9 of 26 (35%) patients showing high or normal F(1+2) levels, respectively (P.025). Mean D-dimer plasma levels were higher in patients than controls (329 [188] ng/mL vs 236 [81] ng/mL; P.01); disease activity was moderate or severe in 6 of 8 (75%) and 11 of 29 (38%) showing elevated or normal plasma D-dimer levels (P = NS). Factor VIIa levels were higher in patients than controls (2.86 ng/mL [0.66] vs 1.97 ng/mL [0.65]; P.001). Activated factor VII and F(1+2) levels were correlated (r = 0.529; P = .008). Tissue factor reactivity was observed only in CU skin specimens.The extrinsic pathway of clotting cascade is activated in CU. Disease severity is associated with the activation of the coagulation cascade.The involvement of the coagulation pathway in CU opens new perspectives for a better understanding of the pathogenesis and, possibly, for the treatment of this disease.

The pro-inflammatory cytokine interleukin (IL)-6 is involved in the pathogenesis of both rheumatoid arthritis (RA) and cardiovascular events. We evaluated the correlation of prothrombotic biomarkers, in particular those of thrombin generation, with inflammatory and clinical parameters in RA patients treated with tocilizumab, an IL-6 receptor (IL-6R) inhibitor. Naïve and maintenance patients were compared.We studied 15 RA patients undergoing tocilizumab infusions at a University Outpatient Clinic. Eight received tocilizumab for the first time and were evaluated at baseline. Seven were in maintenance therapy (9 to 77 months). All 15 patients were evaluated four weeks after the last administration of tocilizumab. At each time, we assessed disease activity score 28 (DAS28), erythrocyte sedimentation rate (ESR) and plasma levels of C-reactive protein (CRP), IL-6, soluble (s)IL-6R, tumour necrosis factor-alpha (TNF-alpha), prothrombin fragment F1+2 and fibrin fragment D-dimer. Forty healthy subjects served as basal controls.At baseline, RA patients showed a moderate-to-high disease activity and median ESR of 51 mm/1(st) hour (interquartile range 25-63). Plasma levels of CRP (p=0.0001), IL-6 (p=0.043), sIL-6R (p=0.003), TNF-alpha (p=0.0001), F1+2 (p=0.0001) and D-dimer (p=0.002) were higher than those of healthy controls. After four weeks we observed reduction of DAS28 (p=0.0001), ESR (p=0.0001), CRP (p=0.014), TNF-alpha (p=0.006), F1+2 (p=0.009) and D-dimer (p=0.04). No differences were observed between naïve and maintenance patients.The reduction of prothrombotic biomarkers parallels the reduction of inflammatory parameters and clinical symptoms in RA patients treated with tocilizumab, both four weeks after the first administration and during maintenance therapy.

A 91-year-old woman affected with acquired Von Willebrand (VW) syndrome and intestinal angiodysplasias presented with severe gastrointestinal bleeding (hemoglobin 5 g/dl). Despite replacement therapy with VW factor/factor VIII concentrate qid, bleeding did not stop (eleven packed red blood cell units were transfused over three days). High circulating levels of anti-VW factor immunoglobulin M were documented immunoenzimatically. Heart ultrasound showed abnormalities of the mitral and aortic valves with severe flow alterations. When intravenous immunoglobulins were added to therapy, prompt clinical and laboratory responses occurred: complete cessation of bleeding, raise in hemoglobin, VW factor antigen, VW ristocetin cofactor and factor VIII levels as well as progressive reduction of the anti-VWF autoantibody levels.

Summary Background Atypical hemolytic uremic syndrome (aHUS) is a thrombotic microangiopathy characterized by hemolysis, platelet consumption, and renal injury. Eculizumab, a mAb that blocks complement activity, has been successfully used in aHUS. Objectives To optimize eculizumab therapy in aHUS patients by monitoring complement functional tests and markers of disease activity. Patients/Methods We studied 18 patients with aHUS (10 males; eight females; age range, 2–40 years) treated with eculizumab to induce and/or maintain disease remission. Patients were followed up for a cumulative observation period of 160 months, during which blood samples were obtained at various time intervals to measure complement activity (Wieslab for the classical, alternative and mannose-binding lectin complement pathways) and the parameters of disease activity (haptoglobin and lactate dehydrogenase serum levels, and platelet count). The intravenous eculizumab doses of 12–33 mg kg−1 were initially administered every week, with the interval between doses being gradually extended to 2 weeks, 3 weeks and 4 weeks on the basis of strict laboratory and clinical control. Results Complement activity was normal before eculizumab treatment, regardless of the state of the disease (activity or remission). It was completely suppressed 1 week, 2 weeks and 3 weeks after the last eculizumab infusion (mean values ± standard deviation: 1% ± 1% to 3% ± 5% for both the classical and alternative pathways; P = 0.0001 vs. baseline), and partially suppressed after 4 weeks (22% ± 26% and 16% ± 27%; P = 0.0001 vs. baseline). The increase in the time interval between eculizumab infusions did not change disease activity markers. Conclusions Monitoring complement tests can allow a safe reduction in the frequency of eculizumab administration in aHUS while keeping the disease in remission.

Background Thrombolysis with recombinant tissue-type plasminogen activator (rt-PA) is successfully used in acute myocardial infarction with ST elevation (STEMI). Reocclusions follow rt-PA treatment in up to 30% of patients within one year. The infusion of rt-PA may induce the production of anti-t-PA antibodies which could interfere with the function of the native t-PA molecule. Methods In order to detect and characterise anti-t-PA antibodies, plasma samples were collected from 30 STEMI patients (20 treated and 10 not treated with rt-PA) at baseline before rt-PA infusion and then 15, 30, 90 and 180 days after STEMI and from 40 healthy subjects at baseline only. Immunoenzymatic, chromatographic and chromogenic methods were employed. Results An increase of anti-t-PA antibodies was observed 15 days (IgM, p = 0.0001) and 30 days (IgG, p = 0.0001) after rt-PA infusion. Six patients had large increases of anti-t-PA IgG which bound the catalytic domain of t-PA (two cases) or kringle 2 domain (four cases), were of IgG1 or IgG3 subclasses and interacted with the t-PA molecule in fluid phase. Conclusion The infusion of rt-PA may induce the production of specific antibodies that bind active sites of t-PA, thus potentially reducing its in vivo function.

Background: Patients with chronic urticaria (CU) frequently show signs of thrombin generation as a result of the activation of the extrinsic pathway of coagulation and signs of fibrinolysis as shown by slightly increased mean D-dimer plasma levels. Here, we studied patients with severe CU to see whether the activation of coagulation and fibrinolysis parallels the severity of the disease. Methods: Eight consecutive patients with severe exacerbations of CU and 13 with slight CU were studied. Plasma prothrombin fragment F 1 + 2 as well as D-dimer were measured by ELISA. Serum histamine-releasing activity was assessed by basophil histamine release assay. Seventy-four normal subjects were used as controls. Results: In patients with severe CU, median levels of both D-dimer (11.20 nmol/ 1) and F 1 + 2 (592 pmol/1) largely exceeded those found in patients with slight CU [D-dimer: 2.66 nmol/1 (P = 0.001) and F 1 +2 : 228 pmol/1 (P = 0.003)] and in normal subjects [D-dimer: 1.41 nmol/l (P = 0.0001) and F 1 + 2 : 159 pmol/1 (P = 0.0001)]. Sera from 25% of patients with severe CU and 31% of those with slight CU, but from none of normal subjects, showed in vitro histamine-releasing activity. D-dimer and F 1 +2 levels were significantly correlated each other (r = 0.64, P = 0.002) and with CU severity score (r = 0.80-0.90, P = 0.0001), but no correlation was observed between serum histamine-releasing activity and coagulation parameters or severity score. Conclusions: Severe exacerbations of CU are associated with a strong activation of coagulation cascade and fibrinolysis. Whether this activation is the cause of CU or acts as an amplification system is still a matter of debate.

Background Previous studies have shown that patients with multiple-drug allergy syndrome (MDAS) frequently have positive autologous serum skin test results, similar to patients with chronic urticaria (CU). Recent investigations have found that patients with CU show signs of thrombin generation and activation of the tissue factor pathway of the coagulation cascade. Objective To study thrombin generation and fibrinolysis in patients with MDAS. Methods Nine patients with MDAS underwent autologous plasma skin testing (APST) and measurement of plasma prothrombin fragment F 1 + 2 and D-dimer levels. Furthermore, the basophil histamine-releasing activity of plasma from patients with MDAS was evaluated. Plasma samples from 74 healthy control subjects and 13 patients with CU were used as negative and positive controls, respectively. Results All 9 patients with MDAS had positive APST results, and 7 showed elevated plasma levels of fragment F 1 + 2 . In patients with MDAS, the median F 1 + 2 level (339 pmol/L; interquartile range [IQR], 250-401 pmol/L) significantly exceeded that in healthy controls (159 pmol/L; IQR, 123-196 pmol/L) ( P = .001) but did not significantly differ from that in controls with CU (292 pmol/L; IQR, 182-564 pmol/L; P = .38). Plasma D-dimer levels were normal in all the patients with MDAS and were significantly lower than in controls with CU ( P = .009). Finally, the histamine-releasing activity of plasma from patients with MDAS was significantly increased and correlated with F 1 + 2 levels ( r = 0.68; P = .04). Conclusion Positive APST results and thrombin generation indicate a common physiopathologic background in MDAS and CU. The lower D-dimer levels suggest that fibrinolysis occurs less intensely in MDAS than in CU.