Evidence for a role of anti-ADAMTS13 autoantibodies despite normal ADAMTS13 activity in recurrent thrombotic thrombocytopenic purpura.

BACKGROUND: Severe ADAMTS13 deficiency is a critical component of the pathogenesis of idiopathic thrombotic thrombocytopenic purpura but is found only in about 60% of patients clinically diagnosed with this disease. DESIGN AND METHODS: Over a period of 8 years and six episodes of thrombotic thrombocytopenic purpura we studied the evolution of the anti-ADAMTS13 antibody response in a patient using different ADAMTS13 assays and epitope mapping. RESULTS: Anti-ADAMTS13 autoantibodies were found in all episodes but were inhibitory only in the last two episodes. In a flow-based assay, normal ADAMTS13 activity was found only during the first disease episode, while ADAMTS13 activity was normal using a static assay in episodes 1 and 3, and severely deficient in the last two episodes. Fluorescence evolution in a modified fluorescence resonance energy transfer assay using a von Willebrand factor A2 domain peptide substrate was linear in episodes 1, 5 and 6, but increased exponentially in episodes 3 and 4. Despite the variable functional characteristics of the anti-ADAMTS13 autoantibodies, their principal epitope was the ADAMTS13 spacer domain in all episodes. CONCLUSIONS: The patient is unique as he displayed features of maturation or shaping of the anti-ADAMTS13 autoantibody response during the course of multiple episodes of thrombotic thrombocytopenic purpura. Anti-ADAMTS13 autoantibodies may be important in vivo despite normal ADAMTS13 activity in routine assays. Consequently, treatment decisions should not be based solely on activity assay results.

Rapid exclusion or confirmation of heparin-induced thrombocytopenia: a single-center experience with 1,291 patients.

BACKGROUND: The current gold-standard for diagnosing heparin-induced thrombocytopenia is the detection of platelet-activating antibodies by means of functional assays which, since they are time consuming and not widely available, are not suited to guiding acute treatment decisions. The objective of our study was to assess the ability of more rapid immunoassays to predict the presence of functionally relevant anti-platelet factor 4/heparin-antibodies. DESIGN AND METHODS: We analyzed 1,291 of 1,383 (93.4%) patients consecutively evaluated for suspected heparin-induced thrombocytopenia at our institution. Clinical pre-test probability was defined by the 4T-score. Anti-platelet factor 4/heparin-antibodies were measured with three immunoassays (ID-H/PF4-PaGIA, Asserachrom-HPIA, and GTI-PF4) and their functional relevance was assessed by a two-point heparin-induced platelet aggregation test. Performance of the immunoassays was evaluated by receiver operating characteristic analysis. RESULTS: Among 1,291 patients, 96 (7.4%) had a positive heparin-induced platelet aggregation-test: 7 of 859 (0.8%) with a low, 50 of 358 (14.0%) with an intermediate, and 39 of 74 (52.7%) with a high 4T-score. Receiver operating characteristics analysis indicated that best immunoassay thresholds for predicting a positive platelet aggregation test were: Titer of 4 or more (ID-H/PF4-PaGIA), optical density more than 0.943 (Asserachrom-HPIA) and more than 1.367 (GTI-PF4). A 100% negative predictive value was observed at the following thresholds: Titer of 1 or under (ID-H/PF4-PaGIA), optical density less than 0.300 (Asserachrom-HPIA) and less than 0.870 (GTI-PF4). A 100% positive predictive value was reached only by ID-H/PF4-PaGIA, at titers of 32 or over. Positive and negative likelihood ratios were calculated for results between the thresholds with 100% negative or positive predictive value. CONCLUSIONS: We show that: i) negative and weak positive results of immunoassays detecting anti-platelet factor 4/heparin-antibodies exclude heparin-induced thrombocytopenia; ii) anti-platelet factor 4/heparin-antibody titers of 32 or over (ID-H/PF4-PaGIA) have a 100% positive predictive value for functionally relevant antibodies; iii) combining the clinical pre-test probability with the likelihood ratio of intermediate immunoassay results allows assessment of post-test probability for heparin-induced thrombocytopenia in individual patients.

Contact system activation in human sepsis - 47kD HK, a marker of sepsis severity?

AIM: This pilot study seeks to determine whether contact system activation (CSA) occurs in human sepsis patients and to characterise blood levels of the 47kD light chain of high-molecular weight kininogen (47kD HK). METHODS: Six consecutive patients with clinical suspicion of sepsis were evaluated on days 1, 2, 3 and 6-8 for 47kD HK blood levels expressed in U/ml of whole blood and as percent of total HK. 47kD HK was measured in whole blood by quantitative immunoblot analysis. RESULTS: On study day 1 or 2, analysis of 47kD HK in U/ml of whole blood identified CSA in 3/6 patients. When 47kD HK levels were expressed as percent of total HK, 4/6 patients were identified with CSA before day 3. The degree of CSA as assayed by the presence of 47kD HK correlated with the severity of the systemic inflammatory syndrome (SIRS), i.e. mean CSA increased progressively from basal levels in healthy controls (0.08 U/ml or 10.4%) to patients without SIRS (0.10 U/ml or 15.1%), to patients with sepsis (0.12 U/ml or 15.0%), and finally to patients in a combined category of severe sepsis and septic shock (0.13 U/ml or 17.4%). CONCLUSION: CSA, defined by increased 47kD HK, occurred early on in the course of sepsis in a subset of sepsis patients. 47kD HK levels, an indicator of bradykinin release, correlated with sepsis severity. Future larger studies will need to evaluate the role of 47kD HK as a biomarker for both prognosis and treatment response in human sepsis..

Stability of coagulation assays performed in plasma from citrated whole blood transported at ambient temperature.

Many preanalytical variables affect the results of coagulation assays. A possible way to control some of them would be to accept blood specimens shipped in the original collection tube. The aim of our study was to investigate the stability of coagulation assays in citrated whole blood transported at ambient temperature for up to two days after specimen collection. Blood samples from 59 patients who attended our haematology outpatient ward for thrombophilia screening were transported at ambient temperature (outdoor during the day, indoor overnight) for following periods of time: <1 hour, 4-6, 8-12, 24-28 and 48-52 hours prior to centrifugation and plasma-freezing. The following coagulation tests were performed: PT, aPTT, fibrinogen, FII:C, FV:C, FVII:C, FVIII:C, FIX:C, FX:C, FXI:C, VWF:RCo, VWF:Ag, AT, PC activity, total and free PS antigen, modified APC-sensitivity-ratio, thrombin-antithrombin-complex and D-dimer. Clinically significant changes, defined as a percentage change of more than 10% from the initial value, were observed for FV:C, FVIII:C and total PS antigen starting at 24-28 hours, and for PT, aPTT and FVII:C at 48-52 hours. No statistically significant differences were seen for fibrinogen, antithrombin, or thrombin-antithrombin complexes (Friedman repeated measures analysis of variance). The present data suggest that the use of whole blood samples transported at ambient temperature may be an acceptable means of delivering specimens for coagulation analysis. With the exception of factor V and VIII coagulant activity, and total PS antigen all investigated parameters can be measured 24-28 hours after specimen collection without observing clinically relevant changes.

Is factor V Leiden a risk factor for thrombotic microangiopathies without severe ADAMTS 13 deficiency?

About 60% of patients diagnosed with acute thrombotic thrombocytopenic purpura (TTP) display a severe ADAMTS13 deficiency. Recently, Raife et al. concluded from a small case series, that factor V Leiden (FVL) might constitute a risk factor for acute thrombotic microangiopathy (TMA) without severe ADAMTS13 deficiency. Therefore, we determined ADAMTS13 activity and FVL carrier-ship in 256 consecutive patients presenting with various forms of acute TMA, including patients diagnosed with TTP or hemolytic-uremic syndrome (HUS). The overall prevalence of FVL was 8.2% (6.25% among patients diagnosed with TTP, and 9% among those with HUS) concordant with the FVL prevalence reported in Europe. FVL was present in 9.9% of patients with ADAMTS 13 activity < 10% and in 9.7% of those with normal ADAMTS13 activity (> 50%). We conclude that FVL is not more prevalent in TMA patients without as compared to those with severe ADAMTS13 deficiency. The prevalence of FVL carriers in certain HUS subgroups (HUS with ADAMTS 13 activity > 50%) reaching 12.3% suggests that a contributory role of FVL in the pathogenesis of defined forms of HUS needs further study.

Administration of C1 inhibitor reduces neutrophil activation in patients with sepsis.

Forty patients with severe sepsis or septic shock recently received C1 inhibitor. In the present study we studied the effect of C1 inhibitor therapy on circulating elastase-alpha(1)-antitrypsin complex (EA) and lactoferrin (LF) levels in these patients to gain further insight about agonists involved in the activation of neutrophils in human sepsis. Elevated levels of EA and LF were found in 65 and 85% of the septic patients, respectively. Patients with elevated EA levels had higher organ dysfunction scores, higher levels of cytokines, and higher levels of complement activation products than patients with normal EA levels. C1 inhibitor therapy reduced EA as well as complement activation and IL-8 release in the patients with elevated EA on admission. We conclude that neutrophil activation in human sepsis correlates with the severity of organ dysfunction and involves complement and interleukin-8 as agonists. The effect of C1 inhibitor therapy on neutrophils may provide an explanation for the beneficial, although mild, effects of this treatment on organ dysfunction in sepsis.

Prekallikrein deficiency: the characteristic normalization of the severely prolonged aPTT following increased preincubation time is due to autoactivation of factor XII.

Hereditary plasma prekallikrein (PK) deficiency was diagnosed in a 71-year-old man with an 8-year history of osteomyelofibrosis. PK deficiency was suspected in view of a severely prolonged activated partial thromboplastin time (aPTT) that nearly normalized following prolonged preincubation (10 min) of patient plasma with kaolin-inosithin reagent. Hereditary PK deficiency was demonstrated by very low PK values in the propositus (PK clotting activity 5%, PK amidolytic activity 5%, PK antigen 2% of normal plasma, respectively) and half normal PK values in his children. Normalization of a severely increased aPTT (>120 s) after prolonged preincubation with aPTT reagent occurred in plasma deficient in PK but not in plasma deficient in factor XII (FXII), high-molecular-weight kininogen (HK), factor XI (FXI), factor IX, factor VIII, Passovoy trait plasma or plasma containing lupus anticoagulant. Autoactivation of FXII in PK-deficient plasma in the presence of kaolin paralleled the normalization of aPTT. Addition of OT-2, a monoclonal antibody inhibiting activated FXII, prevented the normalization of aPTT. We conclude that the normalization of a severely prolonged aPTT upon increased preincubation time (PIT), characteristic of PK deficiency, is due to FXII autoactivation.

Elevated levels of plasma prekallikrein, high molecular weight kininogen and factor XI in coronary heart disease.

Increased levels of hemostatic factors may play a role in the pathogenesis of myocardial infarction by triggering thrombin formation. We measured factor XII (FXII), factor XI (FXI), plasma prekallikrein (PK) and high-molecular-weight kininogen (HK) in 200 patients having survived myocardial infarction for at least 2 months, and in 100 healthy controls. We found significantly elevated levels of FXI clotting activity (FXI:C), HK:C and of the amidolytic activity of PK (PK:Am) among the patients as compared to the controls. Plasma levels of FXI:C, HK:C and PK:Am in the highest quartile were associated with an odds ratio of 1.9 (95% CI: 1.0-3.8), 2.0 (95% CI: 1.0-4.0) and 5.4 (95% CI: 2.6-11.2), respectively, compared to the respective plasma levels in the lowest quartile. After correction for established clinical and laboratory risk factors, the association between PK:Am plasma levels and myocardial infarction remained significant (P=0.0007). Combination of high PK:Am plasma levels and smoking or arterial hypertension, respectively, resulted in a more than additive relative risk for myocardial infarction.