A Rapid and Sensitive Test for Diagnosing Heparin-Associated Thrombocytopenia

Heparin-associated thrombocytopenia (HAT) is a severe complication of heparin therapy. Its diagnosis is difficult. Conventional assays employ platelet aggregometry (PAA) and/or 14C-serotonin release (SRA) which are either insensitive (PAA) or require radioactive tracers (SRA). We here describe a newly developed sensitive and rapid assay based on visual evaluation of heparin-induced platelet activation (HIPA) in microtiter wells. Using sera of 34 patients with clinically suspected HAT we found the HIPA assay to be as sensitive as the SRA and superior to PAA. The HIPA assay allows investigation of crossreactivity with different types of heparins, low molecular weight (LMW) heparins and heparinoids. Three patients who required further parenteral anticoagulation and in whom the HIPA assay was negative before treatment with the LMW heparinoid Org 10172, were treated with this new heparinoid without adverse reactions. We conclude that the HIPA assay may be a useful tool for differential diagnosis and therapy in patients with HAT.

Heparin-Associated Thrombocytopenia: The Effects of Various Intravenous lgG Preparations on Antibody Mediated Platelet Activation - A Possible New Indication for High Dose i.v. IgG

The immunologic type of heparin-associated thrombocytopenia (HAT) is caused by antibodies which activate platelets via the Fc-re- ceptor in the presence of polysulfated oligosaccharides. The antigen is formed by a releasable platelet protein (in many cases PF4) complexed to heparin. Since the role of GP Ilb/IIIa in platelet activation by HAT antibodies is controversial, we investigated platelet activation by antibodies related to HAT. We used normal platelets and platelets from a patient with Glanzmann’s thrombasthenia (GT) lacking GP Ilb/IIIa. Heparin and sera from patients with HAT stimulated GT platelets in the same manner as determined by 14C-serotonin release and the changes in phosphorylation of p20 and p47. Platelet activation could be inhibited by an anti FcRII monoclonal antibody (IV. 3, Fab-fragments), and by Fc-fragments, but not by F(ab’)2-fragments of human IgG. The effect of four different, commercially available preparations of intact i.v. IgG on the platelet activation by six HAT sera was investigated by 14C-seroto- nin release. The inhibitory effect was strongly dependent upon the manufacturing process. At a concentration of 20 mg/ml only IgG that had been subjected to low pH and traces of pepsin sufficiently inhibited platelet activation. IgG treated with polyethylenglycol or sulfitolysis was less effective, whereas beta-propiolactone-treated IgG almost completely lost the ability to inhibit platelet activation by antibodies related to HAT. We conclude that inhibition of GP Ilb/IIIa-fibrinogen interaction is insufficient for preventing platelet activation in HAT. This is, however, possible by high dose i.v. IgG, whereby inhibition of FcRII on platelets strongly depends upon the process by which the i.v. IgG preparation was manufactured.

Heparin-Associated Thrombocytopenia: The Antibody Is Not Heparin Specific

In this study the hypothesis was assessed whether heparin-associated thrombocytopenia (HAT) may be caused by an antibody dependent on polysulfated oligosaccharide epitopes, present not only on heparin but also on different polysulfated substances such as dextran sulfate and pentosan polysulfate. We found that the major factor for eliciting platelet activation with sera of HAT type II patients is neither the structure nor the AT III binding capacity of an oligosaccharide, but rather its grade of sulfation. This was shown by in vitro crossreactivity studies with 40 sera of HAT type II patients using unfractionated heparins, LMW heparins (Fragmin, Fraxiparin), enoxaparin, LMW heparinoid (Org 10172 and its subfractions), de-N-sulfated heparin, dermatan sulfate, dextran sulfate, pentosan polysulfate and dextran. Platelet activation was measured by the heparin induced platelet activation (HIPA) assay and the serotonin release assay (SRA). The platelet activating factor was isolated with the IgG fraction, but did not bind to heparin and dextran sulfate fixed to a solid phase. By isoimmune fixation electrophoresis a monoclonal gammopathy was ruled out in the three sera assessed. The in vivo effect of different LMW heparins and the heparinoid Org 10172 was observed in 10 patients with HAT type II. In a prospective study, a compatible heparin-like anticoagulant was selected for 10 HAT patients for whom further parenteral anticoagulation was required. The only substance that showed no crossreactivity in vitro was the LMW heparinoid Org 10172, which differs from heparin and LMW heparins by its low-grade sulfation. Upon treatment with the heparinoid, all 10 patients had a good clinical outcome, even if they had previously developed thromboembolic complications under LMW heparin administration. As Org 10172 contains a small amount of a LMW heparin-like substance (3%) this heparinoid should not be used in HAT patients without prior in vitro testing. We conclude that heparin-associated thrombocytopenia is not caused by a heparin-specific antibody and that a major factor contributing to the pathomechanism is the high grade of sulfation present in a variety of polysulfated oligosaccharides.

Heparin-induzierte Thrombozytopenie – Pathogenese und Behandlung

Heparin bindet aufgrund seiner negativen Ladung an Thrombozytenproteine. Hierdurch werden Thrombozyten leicht aktiviert. Dies kann bei Krankheiten, bei denen per se die Thrombozyten aktiviert sind, z.B. periphere arterielle Verschlußkrankheiten, zum Abfall der Thrombozyten führen. Diese nicht-immunologischen Wechselwirkungen von Heparin und Thrombozyten sind klinisch von untergeordneter Bedeutung. Viel wichtiger, da in einigen Fällen mit lebensbedrohlichen neuen thromboembolischen Komplikationen verbunden, ist die immunologische Heparin-induzierte Thrombozytopenie (HIT). Betroffene Patienten bilden Antikörper, die an Komplexe aus Thrombozytenproteinen und Heparin binden. Diese Immunkomplexe aktivieren Thrombozyten und Endothelzellen. Dies führt zu einer massiven Verstärkung der Thrombinbildung mit der Konsequenz der Gerinnungsaktivierung. Daher müssen betroffene Patienten weiter antikoaguliert werden. Hierfür stehen vor allem zwei Medikamente zur Verfügung: Rekombinantes Hirudin (Lepirudin, Refludan®) und Danaparoid-Natrium (Orgaran®). Hirudin ist ein direkter Thrombininhibitor, Danaparoid-Natrium zeigt vor allem Anti-Faktor-Xa-Aktivität. Die wichtigsten Therapieoptionen bei ङ IT-Patienten werden in dem Artikel diskutiert.

Heparinoide als eine Alternative für die parenterale Antikoagulation bei Patienten mit Heparin-induzierter Thrombozytopenie

Die Heparin-induzierte Thrombozytopenie (HIT Typ II) ist eine lebensbedrohliche Komplikation der Heparintherapie. Da betroffene Patienten durch diese immunologische, unerwünschte Wirkung der Heparingabe gefährdet sind, neue throm-boembolische Gefäßverschlüsse zu entwickeln, ist bei hinreichendem klinischen Verdacht die sofortige Umstellung auf ein kompatibles Antikoagulans notwendig. Hierfür kommen, neben rekombinantem Hirudin, verschiedene Heparinoide in Betracht. Die Pathophysiologie der HIT Typ II sowie die Struktur und die anti-koagulatorischen Eigenschaften verschiedener Heparinoide werden dargestellt. Der letzte Teil des Artikels faßt den gegenwärtigen Stand der Dosierungsempfehlungen für das Heparinoid Danaparoid (Orgaran®, NV Organon, Niederlande) bei HIT-Typ-Il-Patienten zusammen.

Die Heparin-assoziierte Thrombozytopenie – Immunologische Aspekte

Neben Blutungskomplikationen ist die Heparin-assoziierte Thrombozytopenie (HAT) die wichtigste unerwünschte Wirkung der Heparintherapie. Zwei Formen der HAT werden unterschieden, ein häufiger, nichtimmunologischer Typ I, der einen geringgradigen Abfall der Thrombozyten verursacht und ohne klinische Komplikationen einhergeht, und ein immunologischer Typ II, der mit thromboembolischen Komplikationen verbunden sein kann. Die HAT Typ II tritt zwischen dem 4. und 20. Tag nach Beginn der Heparintherapie auf, mit einem Maximum um den 10. Tag. Im Fall einer Reexposition können sich die klinischen Symptome auch in den ersten Tagen manifestieren. Bei einem Abfall der Thrombozytenwerte um mehr als 50% des Ausgangswertes nach mehreren Tagen Heparintherapie und/oder neuen thromboembolischen Komplikationen während oder kurz nach Beendigung der Heparingabe sollte eine HAT Typ II als wichtige Differentialdiagnose ausgeschlossen werden. Blutungskomplikationen sind sehr selten, die Patienten sind vor allem durch neue Gefäßverschlüsse gefährdet. Der immunologische Typ der HAT ist definiert durch den Nachweis von Heparinabhängigen Antikörpern. Das Hauptantigen der HAT Typ II ist ein multimolekularer Komplex aus Plättchenfaktor 4 und Heparin. Die HAT-Antikörper binden an Thrombozyten und aktivieren diese über ihren Fc-Teil. HAT-Antikörper binden auch an Endothelzellen und aktivieren diese. Die gleichzeitige Aktivierung von Thrombozyten und Endothelzellen ist eine wahrscheinliche Erklärung für den ungewöhnlichen klinischen Verlauf der HAT Typ II. Es stehen mehrere sensitive Testverfahren zur Sicherung der klinischen Verdachtsdiagnose im Labor zur Verfügung. Für die weitere parenterale Antikoagulation betroffener Patienten sind das niedrig sulfatierte Heparinoid Orgaran® oder Hirudin die wichtigsten Medikamente. Beide Substanzen sind jedoch in Deutschland nicht zugelassen.

Platelets kill bacteria by bridging innate and adaptive immunity via platelet factor 4 and FcγRIIA

Essentials Human platelets specifically interact with IgG opsonized bacteria through FcγRIIA. Platelet factor 4 (PF4) binds to polyanions (P) and undergoes a conformational change. Anti-PF4/P IgG opsonizes PF4-coated Gram-positive and Gram-negative bacteria. Platelets specifically kill E.coli opsonized with PF4 and human anti-PF4/P IgG.

SUMMARY

Background Activated platelets release the chemokine platelet factor 4 (PF4) stored in their granules. PF4 binds to polyanions (P) on bacteria, undergoes a conformational change and exposes neoepitopes. These neoepitopes induce production of anti-PF4/P antibodies. As PF4 binds to a variety of bacteria, anti-PF4/P IgG can bind and opsonize several bacterial species. Objective Here we investigated whether platelets are able to kill bacteria directly after recognizing anti-PF4/P IgG opsonized bacteria in the presence of PF4 via their FcγRIIA. Methods Using platelet-bacteria suspension co-culture experiments and micropatterns with immobilized viable bacteria, in combination with pharmacological inhibitors and human anti- PF4/P IgG we analyzed the role of platelet-mediated killing of bacteria. Results In the presence of PF4, human anti-PF4/P IgG and platelets, E. coli killing (> 50%) with colony forming units (CFU mL-1 ) 0.71 × 104 ± 0.19 was observed compared with controls incubated only with anti-PF4/P IgG (CFU mL-1 3.4 × 104 ± 0.38). Blocking of platelet FcγRIIA using mAb IV.3 (CFU mL-1 2.5 × 104 ± 0.45), or integrin αIIbβ3 (CFU mL-1 2.26 × 104 ± 0.31), or disruption of cytoskeletal functions (CFU mL-1 2.7 × 104 ± 0.4) markedly reduced E. coli killing by this mechanism. Our observation of E. coli killing by platelets on micropatterned arrays is compatible with the model that platelets kill bacteria by covering them, actively concentrating them into the area under their granulomere and then releasing antimicrobial substances of platelet α-granules site directed towards bacteria. Conclusion These findings collectively indicate that by bridging of innate and adaptive immune mechanisms, platelets and anti-PF4/polyanion antibodies cooperate in an antibacterial host response.

Preoperative platelet transfusions to reverse antiplatelet therapy for urgent non-cardiac surgery: an observational cohort study

Essentials An increasing number of patients requiring surgery receive antiplatelet therapy (APT). We analyzed 181 patients receiving presurgery platelet transfusions to reverse APT. No coronary thrombosis occurred after platelet transfusion. This justifies a prospective trial to test preoperative platelet transfusions to reverse APT.

SUMMARY

Background Patients receiving antiplatelet therapy (APT) have an increased risk of perioperative bleeding and cardiac adverse events (CAE). Preoperative platelet transfusions may reduce the bleeding risk but may also increase the risk of CAE, particularly coronary thrombosis in patients after recent stent implantation. Objectives To analyze the incidence of perioperative CAE and bleeding in patients undergoing non-cardiac surgery using a standardized management of transfusing two platelet concentrates preoperatively and restart of APT within 24-72 h after surgery. Methods A cohort of consecutive patients on APT treated with two platelet concentrates before non-cardiac surgery between January 2012 and December 2014 was retrospectively identified. Patients were stratified by the risk of major adverse cardiac and cerebrovascular events (MACCE). The primary objective was the incidence of CAE (myocardial infarction, acute heart failure and cardiac troponine T increase). Secondary objectives were incidences of other thromboembolic events, bleedings, transfusions and mortality. Results Among 181 patients, 88 received aspirin, 21 clopidogrel and 72 dual APT. MACCE risk was high in 63, moderate in 103 and low in 15 patients; 67 had cardiac stents. Ten patients (5.5%; 95% CI, 3.0-9.9%) developed a CAE (three myocardial infarctions, four cardiac failures and three troponin T increases). None was caused by coronary thrombosis. Surgery-related bleeding occurred in 22 patients (12.2%; 95% CI, 8.2-17.7%), making 12 re-interventions necessary (6.6%; 95% CI, 3.8-11.2%). Conclusion Preoperative platelet transfusions and early restart of APT allowed urgent surgery and did not cause coronary thromboses, but non-thrombotic CAEs and re-bleeding occurred. Randomized trials are warranted to test platelet transfusion against other management strategies.

An open conformation of ADAMTS-13 is a hallmark of acute acquired thrombotic thrombocytopenic purpura

Essentials Conformational changes in ADAMTS-13 are part of its mode-of-action. The murine anti-ADAMTS-13 antibody 1C4 discriminates between folded and open ADAMTS-13. ADAMTS-13 conformation is open in acute acquired thrombotic thrombocytopenic purpura (TTP). Our study forms an important basis to fully elucidate the pathophysiology of TTP.

SUMMARY

Background Acquired thrombotic thrombocytopenic purpura (aTTP) is an autoimmune disorder characterized by absent ADAMTS-13 activity and the presence of anti-ADAMTS-13 autoantibodies. Recently, it was shown that ADAMTS-13 adopts a folded or an open conformation. Objectives As conformational changes in self-antigens play a role in the pathophysiology of different autoimmune diseases, we hypothesized that the conformation of ADAMTS-13 changes during acute aTTP. Methods Antibodies recognizing cryptic epitopes in the spacer domain were generated. Next, the conformation of ADAMTS-13 in 40 healthy donors (HDs), 99 aTTP patients (63 in the acute phase versus 36 in remission), 12 hemolytic-uremic syndrome (HUS) patients and 63 sepsis patients was determined with ELISA. Results The antibody 1C4 recognizes a cryptic epitope in ADAMTS-13. Therefore, we were able to discriminate between a folded and an open ADAMTS-13 conformation. We showed that ADAMTS-13 in HDs does not bind to 1C4, indicating that ADAMTS-13 circulates in a folded conformation. Similar results were obtained for HUS and sepsis patients. In contrast, ADAMTS-13 of acute aTTP patients bound to 1C4 in 92% of the cases, whereas, in most cases, this binding was abolished during remission, showing that the conformation of ADAMTS-13 is open during an acute aTTP episode. Conclusions Our study shows that, besides absent ADAMTS-13 activity and the presence of anti-ADAMTS-13 autoantibodies, an open ADAMTS-13 conformation is also a hallmark of acute aTTP. Demonstrating this altered ADAMTS-13 conformation in acute aTTP will help to further unravel the pathophysiology of aTTP and lead to improved therapy and diagnosis.

Heparin-induced thrombocytopenia

Heparin-induced thrombocytopenia (HIT), typically occurring in the second week of heparin therapy, is an antibody-mediated adverse drug reaction associated with increased thrombotic risk. The most important antigens are located on platelet factor 4 (PF4)/heparin complexes. HIT is always caused by platelet-activating antibodies, but not all PF4/heparin-reactive antibodies cause HIT. Thus, tests have a high negative, but only a moderate, positive predictive value. Clinical suspicion of HIT requires cessation of heparin and substitution with an alternative anticoagulant. As these drugs have an increased bleeding risk, they should be used in therapeutic doses only if HIT is considered very likely. Avoiding/postponing coumarin is crucial in minimizing microthrombotic complications. Recent studies of HIT immunobiology suggest that HIT mimics immunity against repetitive antigens, as are relevant in microbial defense. Thus, understanding HIT may help unravel why host defenses can trigger autoimmunity.

Heparin-induced Thrombocytopenia – Pathogenesis and Treatment

Heparin-induced thrombocytopenia (HIT) is now recognized as the most frequent immune-mediated adverse drug reaction. During the last decade, fundamental aspects of the pathogenesis of HIT have been resolved. The understanding of some the mechanisms underlying the development of new, paradox thromboembolic complications in HIT led to the concept that thrombin generation plays a key-role in clinically manifest HIT. Consequently new therapeutic concepts imply the use of drugs with either indirect of direct anti-thrombin activity such as donaparoid-sodium and the recombinant hirudin lepirudin. During the last years results of first prospective studies assessing various treatment regimens in HIT became available. Although data of randomized trials are still missing some treatment recommendations can already be drawn from these studies. This review summarizes key aspects of the pathogenesis of HIT and provides an overview of current treatment strategies.

A Comparison of Danaparoid and Lepirudin in Heparin-induced Thrombocytopenia

Heparin-induced thrombocytopenia (HIT) is a hypercoagulable syndrome strongly associated with thrombosis that is usually treated with drugs that inhibit factor Xa (danaparoid) or thrombin (lepirudin). In the present study the outcome of HIT-patients treated with danaparoid or lepirudin was compared using the single or combined endpoints of new thromboembolic complications (new TECs), amputations and/or death, and major bleeding. HIT-patients treated with lepirudin were enrolled in two prospective trials and patients, who were identified in the same two laboratories during the same time period, who were not enrolled into these studies but treated with danaparoid, were assessed retrospectively according to a standardized questionnaire. 126 danaparoid (60.3% female) and 175 lepirudin treated patients (58.3% female) fulfilled the same inclusion and exclusion criteria. In a time-to-eventanalysis the cumulative risk of combined endpoint was higher in HIT-patients without thromboembolic complication at baseline treated with danaparoid (usually in prophylactic dose 750 anti-factor Xa units b.i.d. or t.i.d. s.c.) as compared to lepirudin (aPTT adjusted) (P = 0.020). Whereas HIT-patients with TEC at baseline who were usually treated with therapeutic dose had a similar outcome in both treatment groups (P = 0.913). Major bleeding occurred in 2.5% (95% CI 0.5-7.0%) of danaparoid treated patients as compared to 10.4% (95% CI 6.3-15.9%) of lepirudin treated patients until day 42 (P = 0.009). This indicates that the efficacies of therapeutic doses of danaparoid or lepirudin in preventing death, amputation or new TEC in HIT-patients do not differ largely, but the risk of bleeding seems to be higher in lepirudin treated patients. The prophylactic dose of danaparoid approved in the European Union for HIT without TEC at baseline seems suboptimal. A prospective comparative trial is required to verify these preliminary conclusions.

First Workshop for Detection of Heparin-induced Antibodies: Validation of the Heparin-induced Platelet-activation Test (HIPA) in Comparison with a PF4/Heparin ELISA

Background. No data exist regarding the inter-laboratory reproducibility of the heparin-induced-platelet-activation (HIPA) test, the most widely used functional assay in Germany for the detection of heparin-induced thrombocytopenia (HIT) antibodies. Methods. Nine laboratories used an identical protocol to test eight different sera with the HIPA test. Five laboratories also tested the sera with a platelet factor 4 (PF4)/heparin-complex ELISA. Cross-reactivity with danaparoid-sodium was assessed using 0.2 aFXa units instead of heparin in the HIPA test. Results. Two of nine laboratories had no discrepant HIPA test results. Four laboratories differed in one sample, one reported two discrepant results, and two laboratories reported more than two discrepant results. Cross-reactivity with danaparoid-sodium test results differed among laboratories. PF4/heparin ELISA results were identical in all five laboratories. Conclusion. The HIPA test requires strict quality control measures. Using both a sensitive functional assay (HIPA test) and a PF4/heparin ELISA will allow detection of antibodies directed to antigens other than PF4/heparin complexes as well as detection of IgM and IgA antibodies with PF4/heparin specificity.

Autoimmune heparin-induced thrombocytopenia

Autoimmune heparin-induced thrombocytopenia (aHIT) indicates the presence in patients of anti-platelet factor 4 (PF4)-polyanion antibodies that are able to activate platelets strongly even in the absence of heparin (heparin-independent platelet activation). Nevertheless, as seen with serum obtained from patients with otherwise typical heparin-induced thrombocytopenia (HIT), serum-induced platelet activation is inhibited at high heparin concentrations (10-100 IU mL-1 heparin). Furthermore, upon serial dilution, aHIT serum will usually show heparin-dependent platelet activation. Clinical syndromes associated with aHIT include: delayed-onset HIT, persisting HIT, spontaneous HIT syndrome, fondaparinux-associated HIT, heparin 'flush'-induced HIT, and severe HIT (platelet count of < 20 × 109  L-1 ) with associated disseminated intravascular coagulation (DIC). Recent studies have implicated anti-PF4 antibodies that are able to bridge two PF4 tetramers even in the absence of heparin, probably facilitated by non-heparin platelet-associated polyanions (chondroitin sulfate and polyphosphates); nascent PF4-aHIT-IgG complexes recruit additional heparin-dependent HIT antibodies, leading to the formation of large multimolecular immune complexes and marked platelet activation. aHIT can persist for several weeks, and serial fibrin, D-dimer, and fibrinogen levels, rather than the platelet count, may be helpful for monitoring treatment response. Although standard anticoagulant therapy for HIT ought to be effective, published experience indicates frequent failure of activated partial thromboplastin time (APTT)-adjusted anticoagulants (argatroban, bivalirudin), probably because of underdosing in the setting of HIT-associated DIC, known as 'APTT confounding'. Thus, non-APTT-adjusted therapies with drugs such as danaparoid and fondaparinux, or even direct oral anticoagulants, such as rivaroxaban or apixaban, are suggested therapies, especially for long-term management of persisting HIT. In addition, emerging data indicate that high-dose intravenous immunoglobulin can interrupt HIT antibody-induced platelet activation, leading to rapid platelet count recovery.

Motivational factors for blood donation in first-time donors and repeat donors: a cross-sectional study in West Pomerania

OBJECTIVES

This study aimed to analyse motivational factors for blood donation in different donor groups.

BACKGROUND

As the demographic change will result in a decrease of the population in age groups of blood donors, the risk of blood product shortage increases.

METHODS

During a 12-month period, every sixth blood donor presenting at the blood donation centre of the University Hospital was asked to complete a self-administered questionnaire assessing motivational factors for blood donation. Despite the formalised enrolment protocol, frequent donors were over-represented in the study cohort, which was adjusted by weighting donors with different numbers of donations per year in such a way that the distribution of numbers of donations per year was the same in the sample as in the donor population.

RESULTS

Of 2443 participants, 14·3% were first-time and 85·3% repeat donors. To "help other people" (>90%) and receiving "medical assessment of my blood values" (63-69%) were the strongest motivational factors in all donor groups. Receiving remuneration (49·2% vs 38·1%) was more important for repeat donors than for first-time donors, whereas it was the opposite for "being taken by a friend to the donor clinic" (47·0% vs 15·5%). A potentially important observation is that 33·9% of frequent donors reported feeling physically better after blood donation compared to infrequent donors (29·5%).

CONCLUSION

Identification of motivational factors can lead to the design of targeted motivation campaigns for blood donation. The underlying cause of the perceived well-being after blood donation requires further studies.

Diagnosis of inherited platelet disorders on a blood smear: a tool to facilitate worldwide diagnosis of platelet disorders

Essentials There are many hereditary platelet disorders (HPD) but diagnosing these is challenging. We provide a method to diagnose several HPDs using standard blood smears requiring < 100 µL blood. By this approach, the underlying cause of HPD was characterized in ~25-30% of referred individuals. The method facilitates diagnosis of HPD for patients of all ages around the world.

SUMMARY

Background Many hereditary thrombocytopenias and/or platelet function disorders have been identified, but diagnosis of these conditions remains challenging. Diagnostic laboratory techniques are available only in a few specialized centers and, using fresh blood, often require the patient to travel long distances. For the same reasons, patients living in developing countries usually have limited access to diagnosis. Further, the required amount of blood is often prohibitive for pediatric patients. Objectives By a collaborative international approach of four centers, we aimed to overcome these limitations by developing a method using blood smears prepared from less than 100 μL blood, for a systematic diagnostic approach to characterize the platelet phenotype. Methods We applied immunofluorescence labelling (performed centrally) to standard air-dried peripheral blood smears (prepared locally, shipped by regular mail), using antibodies specific for proteins known to be affected in specific hereditary platelet disorders. Results By immunofluorescence labelling of blood smears we characterized the underlying cause in 877/3217 (27%) patients with suspected hereditary platelet disorders (HPD). Currently about 50 genetic causes for HPD are identified. Among those, the blood smear method was especially helpful to identify MYH9 disorders/MYH9-related disease, biallelic Bernard-Soulier syndrome, Glanzmann thrombasthenia and gray platelet syndrome. Diagnosis could be established for GATA1 macrothrombocytopenia, GFI1B macrothrombocytopenia, ß1-tubulin macrothrombocytopenia, filamin A-related thrombocytopenia and Wiskott-Aldrich syndrome. Conclusion Combining basic and widely available preanalytical methods with the immunomorphological techniques presented here, allows detailed characterization of the platelet phenotype. This supports genetic testing and facilitates diagnosis of hereditary platelet disorders for patients of all ages around the world.

Platelet activation in the presence of neutral protamine Hagedorn insulin: a new feature of antibodies against protamine/heparin complexes

Essentials Protamine (PRT) is used to stabilize insulin in neutral protamine Hagedorn (NPH) insulin. The interaction between NPH-insulin, anti-PRT/heparin antibodies and platelets was investigated. Anti-PRT/heparin antibodies activate platelets in presence of NPH-insulin dependent on heparin. Cross-reactivity seems to have no major effect on the clinical outcome of medical patients.

SUMMARY

Background Protamine (PRT) is used to stabilize insulin in neutral protamine Hagedorn (NPH) insulin, a commonly used therapeutic agent for diabetes mellitus. Immunization against PRT/heparin complexes is common in diabetic patients. Objectives To investigate the impact of NPH-insulin on the interaction between anti-PRT/heparin antibodies and platelets. Methods The interaction between NPH-insulin and anti-PRT/heparin antibodies was tested using in-house enzyme immunoassays. The ability of anti-PRT/heparin antibodies to activate platelets in the presence of NPH-insulin (and heparin) was investigated using flow cytometry. Results Twenty-one out of 80 sera containing anti-PRT/heparin IgG showed binding to NPH-insulin. Anti-PRT/heparin IgG from immunized patients bound to platelets in the presence of NPH-insulin, but not in the presence of native insulin. Anti-PRT/heparin antibodies induced P-selectin expression in the presence of NPH-insulin in a heparin-dependent way (median mean fluorescence intensity in the presence of NPH-insulin: 55, 95% confidence interval [CI] 18.7-100.5 vs. NPH-insulin and heparin: 204, 95% CI 106.5-372.8). The clinical relevance of platelet-activating anti-PRT/heparin antibodies was assessed by investigating a multicenter study cohort of 332 acutely ill medical patients who received heparin. None of the 21 patients with anti-PRT/heparin IgG developed thrombocytopenia or thromboembolic complications. Conclusions Anti-PRT/heparin antibodies activate platelets in the presence of NPH-insulin in a heparin-dependent way. However, results from our preliminary study indicate no major impact of these antibodies on the clinical outcome in medical patients receiving heparin, particularly on thromboembolic complications.

Implications of a switch to a 100% apheresis platelet supply for patients and for blood donors: a risk benefit analysis

BACKGROUND

A 100% apheresis platelet supply is considered to increase transfusion safety by lowering donor exposures for transfusion recipients. We performed a risk benefit analysis to contrast the reduction of donor exposures and the risk of contaminated blood products in the nation-wide inventory with the donor risks associated with a switch to a 100% apheresis platelet supply in Germany.

METHODS

Donor exposures and the number of contaminated blood products resulting from HIV-like, HBV-like, HCV-like pathogens and two theoretical agents with infection rates of 10 and 1000 in 100 000, respectively, were calculated for a 100% apheresis platelet supply in Germany based on the 2006-2012 hemovigilance reports. These numbers were compared with the current mixed platelet supply of pooled and apheresis platelets. Moreover, additional donation time and apheresis donor complications resulting from a 100% apheresis platelet supply were estimated.

RESULTS

Per million total blood products (red cells, platelets, fresh frozen plasma), a 100% apheresis platelet supply would reduce donor exposures by 87 100 and the number of contaminated blood products ranging from 0·8 to 871·1. On the other hand, this requires additional 29 478 apheresis donations, 3·4 years additional donor time, and would be associated with 58 additional donor complications, respectively.

CONCLUSIONS

A 100% apheresis platelet supply would reduce donor exposures and the number of contaminated blood products in the inventory, but would increase apheresis complications in donors. Potential risks for patients must be carefully weighed against the risks for donors, dependent on the specific pathogen scenario.

Predonation finger lancet punctures: a potential risk factor for interdonor pathogen transmission in the blood donor clinic

BACKGROUND AND OBJECTIVES

Point-of-care testing using capillary blood from a finger prick is widely used for predonation haemoglobin testing of blood donors. It is common practice to cover the finger prick with a cotton swab and to instruct the donor to press for few minutes. The finger prick can cause blood contamination of surfaces in contact with the lanced finger, especially door handles, risking infectious disease transmission, particularly if another person touching the contaminated door handle also has a punctured fingertip.

MATERIALS AND METHODS

First, we investigated contamination by blood (benzidine assay) of the door handles of our blood donor clinic, taking 175 samples 3 h after opening of the donation centre (baseline). We then introduced band-aids to cover the finger prick and started an information campaign using educational flyers to sensitize blood donors and staff to this problem (period-1). Thereafter, the staff was instructed to use the non-dominant hand for blood sampling and mandated to replace any discarded band-aids immediately (period-2).

RESULTS

At baseline, 82% of the nurse room door handles showed contamination with blood. This decreased somewhat (10-40%) after period-1, but only after immediate mandatory band-aid replacement on any donor finger without a band-aid (period-2), no further blood contaminations were detected.

CONCLUSION

Blood contamination of shared surfaces can occur after finger prick for capillary blood sampling. Application of a band-aid and use of the non-dominant hand for fingertip incision are easy to apply and effective in reducing this iatrogenic health hazard.

HNA antibody-mediated neutrophil aggregation is dependent on serine protease activity

BACKGROUND AND OBJECTIVES

Transfusion-related acute lung injury (TRALI) is often caused by antibodies against human neutrophil alloantigen-2 (HNA-2) and HNA-3a. Neutrophil aggregation is considered as a major cause of TRALI, but little is known about how HNA antibodies initiate this process. We explored mechanisms involved in neutrophil aggregation induced by HNA-2 and HNA-3a antibodies.

MATERIALS AND METHODS

Isolated neutrophils were pretreated with broad-spectrum or specific inhibitors against different cell functions or proteases. Granulocyte agglutination test (GAT) was performed with serially diluted anti-HNA-2 and anti-HNA-3a plasmas or control plasma, and reactivity was evaluated microscopically. Reactive oxygen species (ROS) production in neutrophils was investigated using a lucigenin-based chemiluminescence assay.

RESULTS

HNA-2 and HNA-3a antibody-mediated neutrophil aggregation was inhibited by pretreatment with formaldehyde, iodoacetamide and the serine protease inhibitors Pefabloc-SC, N-p-tosyl-L-phenylalanine chloromethyl ketone (TPCK) and Nα-tosyl-L-lysine chloromethyl ketone hydrochloride (TLCK). In contrast, inhibition of actin polymerization, respiratory burst, cysteine proteases, metalloproteases or aspartic proteases did not affect neutrophil aggregation. Furthermore, HNA-3a antibodies did not directly cause ROS production in neutrophils.

CONCLUSION

Aggregation of neutrophils induced by HNA-2 and HNA-3a antibodies is an active process and depends on trypsin- or chymotrypsin-like serine proteases but is not dependent on the production of ROS. These findings may open new prospects for the pharmacologic prevention of neutrophil-associated acute lung injury.

[Hemostatic management of patients undergoing ear-nose-throat-surgery]

Perioperative hemostatic management is increasingly important in Otolaryngology. This review summarizes the key elements of perioperative risk stratification, thromboprophylaxis, and therapies for bridging of antithrombotic treatment. It gives a practical advise based on the current literature with an emphasis for patients undergoing ear-nose-throat surgery.

Tolerance of platelet concentrates treated with UVC-light only for pathogen reduction--a phase I clinical trial

BACKGROUND

The THERAFLEX UV-Platelets pathogen reduction system for platelet concentrates (PCs) operates with ultraviolet C light (UVC; 254 nm) only without addition of photosensitizers. This phase I study evaluated safety and tolerability of autologous UVC-irradiated PCs in healthy volunteers.

METHODS

Eleven volunteers underwent two single (series 1 and 2) and one double apheresis (series 3). PCs were treated with UVC, stored for 48 h and retransfused in a dose-escalation scheme: 12·5, 25% and 50% of a PC (series 1); one complete PC (series 2); two PCs (series 3). Platelet counts, fibrinogen, activated partial thromboplastin time, prothrombin time, D-dimer, standard haematology, temperature, heart rate, blood pressure and clinical chemistry parameters were measured. One- and 24-h corrected count increments were determined in series 2 and 3. Platelet-specific antibodies were assessed before and at the end of the study.

RESULTS

Neither adverse reactions related to transfusions nor antibodies against UVC-treated platelets were observed. Corrected count increments did not differ between series 2 and 3.

CONCLUSIONS

Repeated transfusions of autologous UVC-treated PCs were well tolerated and did not induce antibody responses in all volunteers studied. EudraCT No. 2010-023404-26.

Anti-platelet factor 4/heparin antibodies in patients with impaired graft function after liver transplantation

BACKGROUND

Heparin, the standard perioperative anticoagulant for the prevention of graft vessel thrombosis in patients undergoing liver transplantation (LT), binds to the chemokine platelet factor 4 (PF4). Antibodies that are formed against the resulting PF4/heparin complexes can induce heparin-induced thrombocytopenia. LT is a clinical situation that allows the study of T-cell dependency of immune responses because T-cell function is largely suppressed pharmacologically in these patients to prevent graft rejection.

OBJECTIVES

To investigate the immune response against PF4/heparin complexes in patients undergoing LT.

PATIENTS AND METHODS

In this prospective cohort study, 38 consecutive patients undergoing LT were systematically screened for anti-PF4/heparin antibodies (enzyme immunoassay and heparin-induced platelet aggregation assay), platelet count, liver function, and engraftment.

RESULTS

At baseline, 5 (13%) of 38 patients tested positive for anti-PF4/heparin IgG (non-platelet-activating) antibodies. By day 20, an additional 5 (15%) of 33 patients seroconverted for immunoglobulin G (two platelet-activating) antibodies. No patient developed clinical heparin-induced thrombocytopenia. Two of six patients with graft function failure had anti-PF4/heparin IgG antibodies at the time of graft function failure. Graft liver biopsy samples from these patients showed thrombotic occlusions of the microcirculation.

CONCLUSIONS

Anti-PF4/heparin IgG antibodies are generated despite strong pharmacologic suppression of T cells, indicating that T cells likely have a limited role in the immune response to PF4/heparin complexes in humans.

Characterisation of the conformational changes in platelet factor 4 induced by polyanions: towards in vitro prediction of antigenicity

Heparin-induced thrombocytopenia (HIT) is the most frequent drug-induced immune reaction affecting blood cells. Its antigen is formed when the chemokine platelet factor 4 (PF4) complexes with polyanions. By assessing polyanions of varying length and degree of sulfation using immunoassay and circular dichroism (CD)-spectroscopy, we show that PF4 structural changes resulting in antiparallel β-sheet content >30% make PF4/polyanion complexes antigenic. Further, we found that polyphosphates (polyP-55) induce antigenic changes on PF4, whereas fondaparinux does not. We provide a model suggesting that conformational changes exposing antigens on PF4/polyanion complexes occur in the hairpin involving AA 32-38, which form together with C-terminal AA (66-70) of the adjacent PF4 monomer a continuous patch on the PF4 tetramer surface, explaining why only tetrameric PF4 molecules express "HIT antigens". The correlation of antibody binding in immunoassays with PF4 structural changes provides the intriguing possibility that CD-spectroscopy could become the first antibody-independent, in vitro method to predict potential immunogenicity of drugs. CD-spectroscopy could identify compounds during preclinical drug development that induce PF4 structural changes correlated with antigenicity. The clinical relevance can then be specifically addressed during clinical trials. Whether these findings can be transferred to other endogenous proteins requires further studies.