Hartmut Kroll

Clinical features of heparin-induced thrombocytopenia including risk factors for thrombosis A retrospective analysis of 408 patients

Immune mediated heparin induced thrombocytopenia (HIT) is a prothrombotic adverse effect of heparin. However, only a subgroup of patients with HIT develops thromboembolic complications. We aimed to identify risk factors for developing HITassociated thrombosis. We analyzed a registry of patients with clinical suspicion of HIT who tested positive using a sensitive functional assay. Patient information was obtained by a standardized questionnaire. By multivariate analysis the association of age, gender, type of patient population, and magnitude of the platelet count decline with the frequency, type (venous or arterial), and temporal pattern of thrombotic events was assessed. In 408 HIT patients we observed predominance of venous thrombosis (2.4:1), with 40% of patients developing a pulmonary embolism. However, in the subgroup of post-cardiovascular surgery patients there was predominance of arterial thrombosis (1:8.5). The type of arterial thrombosis (limb artery thrombosis > thrombotic stroke > myocardial infarction) was the converse of that observed with typical atherothrombotic clots in non-HIT populations. In 59.8% of patients HIT-related thrombosis manifested either on the same day a platelet count decrease >50% was documented (26.3%) or before the decrease in platelet counts (33.5%). The most important risk factors for thrombosis were orthopedic/trauma surgery and the magnitude of platelet count decrease. HIT-associated thrombosis occurs in a considerable proportion of patients before platelet counts decrease by more than 50%.

HPA‐5b (Bra) neonatal alloimmune thrombocytopenia: clinical and immunological analysis of 39 cases

Summary. Maternal alloimmunization against fetal platelets can cause fetal and neonatal thrombocytopenia (NAIT). The HPA‐1a (PIA1, Zwa) antigen is by far the most common antigen implicated in NAIT. However, today another antigen often linked with that affection is HPA‐5b (Bra). This is a report of 39 cases of NAIT involving the HPA‐5b antigen. Thrombocytopenia may be of grave consequence. Three infants developed intracerebral haemorrhages (ICH). Of these, one died presumably as a consequence of ICH. Central nervous system (CNS) sequelae in the neonatal period was observed in two children. The potential hazards of death or disabling neurologic sequelae following intracerebral haemorrhage call for rapid and reliable diagnosis and effective therapy. Because there is high risk that subsequent pregnancies might be also affected by NAIT, the mothers of a previously affected child should be managed similarly to the HPA‐1b mothers (PIA2, Zwb). The antenatal diagnosis of thrombocytopenia should be made and if necessary the in utero therapy instituted.

European collaborative study of the antenatal management of feto‐maternal alloimmune thrombocytopenia

Summary. The aims of this study were to determine whether the severity of fetomaternal alloimmune thrombocytopenia (FMAIT) in the current pregnancy could be predicted from the history of FMAIT in previous pregnancies, and to assess the effects of different types of antenatal intervention. Fifty‐six fetuses were studied that all had a sibling affected by FMAIT due to human platelet antigen 1a (HPA‐1a) alloimmunization. Cases with a sibling history of antenatal intracranial haemorrhage (ICH) or severe thrombocytopenia (platelet counts of < 20 × 109/l) had significantly lower pretreatment platelet counts than cases whose siblings had less severe thrombocytopenia or postnatal ICH. Maternal therapy resulted in a platelet count exceeding 50 × 109/l in 67% of cases. None of the fetuses managed by serial platelet intrauterine transfusions (IUT) suffered ICH following treatment. However, several serious complications arose with fetal blood sampling (FBS). Overall, intervention improved outcome, as three study cases suffered from antenatal ICH and three others died whereas 15 study cases had a sibling with an ICH, eight of whom died. The results of this study suggest that the start of therapy can be stratified on the basis of the sibling history of FMAIT, and support the use of maternal therapy as first‐line treatment.

Platelet alloantibodies in transfused patients

BACKGROUND: Patients receiving cellular blood components may form HLA antibodies and platelet‐specific alloantibodies.

Clinical Aspects and Typing of Platelet Alloantigens

Platelet alloantigens can induce the formation of corresponding alloantibodies when exposed to phenotypically negative individuals. These antibodies are responsible for fetal and neonatal alloimmune thrombocytopenia, posttransfusion purpura, passive alloimmune thrombocytopenia and transplantation‐ associated thrombocytopenia and may contribute to platelet transfusion refractoriness together with HLA antibodies. Besides antibody detection laboratory diagnosis of the clinical syndromes requires alloantigen typing. Furthermore, typed platelet donors are a prerequisite for effective platelet transfusion therapy. Different techniques for phenotyping are well established and easy to perform but they rely on the availability of antisera. Since the molecular genetic background of the clinically most relevant alloantigens has been elucidated during the last years various genotyping methods have been applied to the platelet membrane polymorphisms and thus facilitated widespread platelet alloantigen typing. Generation of antibodies from phage display libraries and of lymphoblastoid cell lines from donors with all genetic variants will allow further developments.

Genomic RFLP typing of human platelet alloantigens Zw(PlA), Ko, Bak and Br (HPA-1, 2, 3, 5).

Summary. The diallelic human platelet alloantigen systems 1–5 have been found to result from single base pair substitutions in the encoding genes of platelet membrane glycoproteins IIIa, Ib, IIb and Ia. This is the basis of DNA methods for determination of platelet alloantigens. In this study, 98 blood donors were typed in the HPA‐1, 2, 3 systems and, for the first time, in the HPA‐5 system. Serologically obtained data (MAIPA and platelet agglutination) were compared with results from analysis of restriction fragment length polymorphisms (RFLP). Discordances were found in the HPA‐2 and 3 systems and can be ascribed to false typing results in both the serological and genomic methods. In the HPA‐1, 2 and 5 systems, all samples were typed correctly with RFLP analysis. Serologically, two donors were falsely typed positive with anti‐HPA‐2b in platelet agglutination and one donor with anti‐HPA‐3a in MAIPA assay. In the HPA‐3 system, another four donors were misinterpreted to be HPA‐3 a negative in RFLP analysis. Possible technical problems in PCR‐RFLP‐typing are discussed and another strategy of HPA‐1 typing using the restriction enzyme Scr FI is evaluated.

Maternal intravenous immunoglobulin treatment does not prevent intracranial haemorrhage in fetal alloimmune thrombocytopenia

SUMMARY. In fetal alloimmune thrombocytopenia (FAIT) the fetus is threatened by intracranial haemorrhage (ICH); therefore early diagnostic and therapeutic intervention is required. We followed the clinical course of a 30‐year‐old woman during her fifth pregnancy after she had given birth to a child with alloimmune thrombocytopenia due to anti‐Zwa. The fetus was monitored by 13 fetal blood samplings (FBS) always followed by transfusion of either maternal or compatible donor platelets. Intravenous immunoglobulin (ivIg) treatment of the mother was begun at 20 weeks of gestation when the fetal platelet count was 36 times 109/1. The fetal platelets were typed Zwa positive by DNA analysis. Despite 11 weeks of maternal ivIg treatment fetal platelet counts progressively declined to 6 times 10/1 and ICH occurred. Subsequently, the fetus was successfully managed by intrauterine platelet transfusions at shorter intervals (3–5 days) and elective Cesarean section was carried out at 35 weeks of gestation. We conclude that maternal ivIg treatment does not prevent ICH in FAIT. The treatment of choice for severely affected cases is serial FBS combined with transfusion of compatible platelets.

348 cases of suspected neonatal alloimmune thrombocytopenia

pump to allow pulsatile tocolytic infusion, hoping to reduce the total dose and thus the side effects. In 33 patients pulsatile bolus tocolysis was compared with continuous tocolysis in a control group of 38 patients. Bolus tocolysis required considerably less beta-sympathomimetic agent for comparable therapeutic success (median dosage 3.0 versus 15.9 mg, P < 0.001). Duration of therapy under bolus tocolysis was also significantly shorter (P < 0.05). Birth weight was higher after bolus tocolysis (median 3,070 versus 2,580 gm, P = 0.05). Additional indicators favored bolus tocolysis but were not statistically significant: a longer gestational period, fewer infants weighing < 2500 gm, and a lower incidence of respiratory distress syndrome. Pulmonary edema occurred in one patient during continuous tocolysis.

Relevance of the HPA-15 (Gov) polymorphism on CD109 in alloimmune thrombocytopenic syndromes

BACKGROUND: Alloantibodies against the human platelet (PLT) alloantigen (HPA)‐15 system residing on CD109 can cause fetal and neonatal alloimmune thrombocytopenia (FNAIT), posttransfusion purpura, and PLT transfusion refractoriness. The detection of antibodies against HPA‐15, however, is hampered by the variable low expression and instability of the CD109 molecule during preparation and storage.

HLA‐DRw6, a New Immune Response Marker for Immunization against the Platelet Alloantigen Bra

We have recently detected a new platelet alloantigen, Br a , which also belongs to a diallelic system (Br a /Br b ) and resides on glycoprotein Ia. Maternal immunization against the Br a antigen of the fetus is the second most frequent cause of neonatal alloimmune thrombocytopenia in the German population. We here report a strong association of Br a immunization with the presence of HLA-DRw6