Post-transfusion purpura: a survey of 12 Danish cases with special reference to immunoglobulin G subclasses of the platelet antibodies

Transfusion Reactions and Adverse Events

Blood transfusions are generally safe but can carry considerable risks. This review summarizes the different types of transfusion reactions and ways to diagnose and manage them. Symptoms are often overlapping and nonspecific. When a reaction is suspected, it is critical to stop the transfusion immediately and report the reaction to the blood bank, as this can affect the patient's outcome. New evidence-based algorithms of transfusion, newer blood screening methods and donor policies and deferrals, new laboratory testing, electronic verification systems, and improved hemovigilance lead to the avoidance of unnecessary transfusions and decrease the incidence of serious transfusion reactions.

Post-Transfusion Purpura: Current Perspectives

Post transfusion purpura (PTP) is an uncommonly reported post transfusion adverse event that can present with severe thrombocytopenia; sometimes resulting in significant bleeding and hemorrhage. Its diagnosis can be elusive given its substantial symptomatic overlap with other thrombocytopenic syndromes. Underdiagnosis and underreporting make the true incidence of disease difficult to define. While clinical suspicion is key, laboratory evidence of platelet-targeted antibodies and identification of the antigen(s) they recognize are necessary to confirm the diagnosis. A curious aspect of PTP is paradoxical destruction of both transfused and autologous platelets. Although the first case was reported over 50 years ago, this aspect of PTP pathogenesis is still not fully understood and is widely debated. Several theories exist, but conclusive evidence to support most is lacking. Despite limited understanding of disease incidence and etiology, treatment with IVIG (Intravenous Immunoglobulin) has become standard practice and can be highly effective. Although recurrence is rare, precautions should be taken if patients with a history of PTP require transfusions in the future.

Anti-HPA-1b Mediated Posttransfusion Purpura: A Case Report

Posttransfusion purpura (PTP) is an uncommon, but potentially fatal, transfusion reaction characterized by profound thrombocytopenia and bleeding. PTP is caused by alloimmunization to human platelet specific antigens following blood component transfusion. Although there is evidence of a wide serological spectrum of culprit antibodies implicated, Anti-human-platelet-antigen- (HPA-) 1a is the most common antibody in cases reported. We report a case of posttransfusion purpura in an African American. The patient was negative for HPA-1a antibodies, but anti-HPA-1b was identified with a platelet phenotype of HPA-1a/HPA-1a. Although less common, HPA-1b antibody may be an important consideration in posttransfusion purpura diagnosed in patients of African descent.

Sensitivity of assays for the detection of HPA-1a antibodies: results of an international workshop demonstrating the impact of cation chelation from integrin αIIbβ3 on three widely used assays

BACKGROUND AND OBJECTIVES

HPA-1a antibodies account for 70-80% of cases of fetal-neonatal alloimmune thrombocytopenia (FNAIT) in Caucasians. However, numerous workshops have demonstrated variability in their detection. We recently showed that exposure of αIIbβ3 to ethylene diamine tetraacetic acid (EDTA) affected binding of many anti-αIIbβ3 monoclonal, and HPA-1a allo-, antibodies; this adversely affected sensitivity of the monoclonal antibody-specific immobilization of platelet antigens (MAIPA) assay and indirect platelet immunofluorescence test (PIFT). This study presents results from an international workshop studying the impact of cation chelation on HPA-1a antibody detection in routine diagnostic laboratories.

MATERIALS AND METHODS

Serum and EDTA-anticoagulated plasma samples containing anti-HPA-1a were distributed to 39 laboratories. Participants were asked to detect and identify any HPA antibodies present.

RESULTS

2/39 (5.1%) participants were able to detect and identify anti-HPA-1a in the serum, but not in the plasma sample. EDTA plasma reduced MAIPA assay sensitivity by ≥ 20% in 17/24 (70.8%) laboratories and by ≥ 50% in 9/24 (37.5%) when using HPA-1a1a platelets (mean: 27.7%, range 0-85.1%); when using HPA-1a1b platelets 3/4 (75%), participants reported ≥ 50% loss of sensitivity (mean 65.6%, range 0-96.6%). A small but significant increase in optical densities was observed in antigen capture ELISA assays when using plasma (mean difference: 0.081, P < 0.01). Insufficient PIFT data were returned to draw firm conclusions.

CONCLUSION

Use of EDTA plasma significantly affects the sensitivity of the MAIPA assay and can affect detection of even potent, FNAIT-causing examples of anti-HPA-1a. These data highlight the importance of use of αIIbβ3 in an appropriate conformation for the sensitive detection of anti-HPA-1a.

The impact of universal leukodepletion of the blood supply on hemovigilance reports of posttransfusion purpura and transfusion-associated graft-versus-host disease

BACKGROUND

The pathogenesis of posttransfusion purpura (PTP) and transfusion-associated graft-versus-host disease (TA-GVHD) involves patient exposure to donor platelets (PLTs) and T lymphocytes, respectively, which are removed during blood component leukodepletion (LD).

STUDY DESIGN AND METHODS

Reports of PTP and TA-GVHD to the UK hemovigilance scheme Serious Hazards of Transfusion (SHOT) from 1996 to 2005 were compared before and after implementation of universal LD during 1999.

RESULTS

There were 45 reports of PTP, with a mean of 10.3 per year before universal LD and 2.3 per year afterward (p < 0.001). All patients had received red cells, but before universal LD, only 1 of 31 (3%) cases had also received PLTs, compared to 8 of 14 (57%) afterward (p < 0.001). Thirty-four cases (76%) had human platelet antigen (HPA)-1a antibodies, whereas 11 had antibodies to other HPA specificities, only 1 of which occurred after LD. Two cases reported before LD also had heparin-dependent PLT antibodies. There were 13 reports of TA-GVHD, all fatal, of which only 2 cases of undiagnosed immunodeficiency met current UK criteria for irradiated components. Eight others had one or more risk factors: B-cell malignancy (6), steroids (1), fresh blood (1), and donor-recipient HLA haplotype share (4). Eleven cases were due to non-LD and 2 to LD components (p < 0.001). No cases have been reported since 2001. In an additional 405 cases, nonirradiated components were transfused in error to high-risk recipients, mainly on fludarabine, but none developed TA-GVHD.

CONCLUSIONS

These findings suggest that universal LD has further reduced the already low risk of TA-GVHD in immunocompetent recipients and has altered the profile of PTP cases.

Post-transfusion purpura (PTP) and disseminated intravascular coagulation (DIC)

A 47-yr-old female with acute pancreatitis received four units of fresh frozen plasma because of subtle signs of disseminated intravascular coagulation (DIC). Seven days later, she developed severe thrombocytopenia. Serological studies demonstrated antibodies against HPA-1a together with pan-reactive antibodies against platelet glycoproteins (GPIIb-IIIa, GPIb-IX and GPIa-IIa), which was consistent with the diagnosis of PTP. The patient was treated with platelet transfusions, corticosteroids and intravenous immunoglobulin (IVIG) without permanent beneficial effect. After treatment with plasma exchange the platelet count increased to normal values.

Semiquantitative measurement of IgG subclasses and IgM of platelet-specific antibodies in a glycoprotein-specific platelet-antigen capture assay

The detection of platelet-specific antibodies is of high clinical interest in diseases with immune thrombocytopenia. The glycoprotein-specific platelet-antigen capture (PAC)-assay developed in this study is especially suited to the differentiation of platelet-specific immunoglobulin (Ig) G subclasses and the determination of platelet-specific IgM in serum or on platelets. The problems with unspecific signals or low sensitivity usually seen with the detector antibodies available are effectively overcome, as unbound detector antibodies are removed at an early stage in the assay. We investigated 14 maternal alloantisera from cases of neonatal alloimmune thrombocytopenia (NAITP) and six sera from patients with autoimmune thrombocytopenic purpura (AITP). In NAITP sera, we found IgG1 alone in 57%, IgG1 + IgG3 in 21% and IgG1 + IgG2 in 14% of cases. One serum contained IgG1 + IgG2 + IgG3. In AITP, three out of the six sera contained IgG1 alone. One serum contained IgG1 + IgG2. One patient, with highly refractory AITP, had platelet-specific IgG1 + IgG2 + IgG3 in his serum. A patient with AITP in remission and normal platelet counts only showed platelet-bound IgG2. The detection of platelet-specific 'whole IgG' is possible too. However, at this time the commonly used monoclonal antibody-specific immobilization of platelet antigens (MAIPA) method should not be replaced for this purpose, as it is well standardized and used with similar results in many laboratories. The PAC assay sensitively detects the subclasses of platelet-specific IgG and human leucocyte antigen (HLA)-antibodies independently. It is easy to perform and takes less time than other platelet glycoprotein-specific methods.

Human platelet antigen-1a antibodies induce the release of the chemokine RANTES from human platelets

BACKGROUND AND OBJECTIVE

Binding of human platelet antigen-1a (HPA-1a)-specific antibodies to target platelets can trigger platelet activation and mediator release. Here we tested the effect of HPA-1a antibody-containing sera on platelet release of the chemokine RANTES (regulated on activation, normal, T-cell expressed, and presumably secreted) in vitro.

PATIENTS AND METHODS

HPA-1a-containing sera obtained from 11 mothers delivered of an infant with neonatal alloimmune thrombocytopenia (NAIT) and from six patients with post-transfusion purpura (PTP) were incubated with HPA-1a/a target platelets. Antibody-induced release of soluble RANTES was determined by enzyme-linked immunosorbent assay (ELISA).

RESULTS

A significant release of soluble RANTES was induced by four out of the 17 sera. Two out of the four reactive sera were obtained from mothers who were delivered of a baby with NAIT and the remaining two sera were from patients with PTP. Chemokine release was specific for binding of anti-HPA-1a to the platelet membrane, as none of the reactive sera induced the release of soluble RANTES when incubated with HPA-1b/b platelets. The blockade of platelet-expressed Fc gamma receptor type II (FcgammaRII) inhibited anti-HPA-1a-mediated RANTES release when incubated with the reactive sera of patients with NAIT, but not when platelets were incubated with sera of patients with PTP.

CONCLUSION

Our findings suggest that anti-HPA-1a antibody-induced release of platelet-derived RANTES can play a role in adverse reactions in alloimmunized patients.

Non-infectious complications of transfusion therapy

Blood transfusion is considered safe when the infused blood is tested using state of the art viral assays developed over the past several decades. Only rarely are known viruses like HIV and hepatitis C transmitted by transfusion when blood donors are screened using these sensitive laboratory tests. However, there are a variety of transfusion risks which still remain that cannot be entirely eliminated, many of which are non-infectious in nature. Predominantly immune-mediated complications include the rapid intravascular or slow extravascular destruction (hemolysis) of transfused red cells or extravascular removal of platelets by pre-formed antibodies carried by the transfusion recipient. Alternatively, red cells can be damaged when exposed to excessive heat or incompatible intravenous fluids before or during the transfusion. Common complications of blood transfusion that at least partly involve the immune system include febrile non-hemolytic and allergic reactions. While these are usually not life-threatening, they can hamper efforts to transfuse a patient. Other complications include circulatory overload, hypothermia and metabolic disturbances. Profound hypotensive episodes have been described in patients on angiotensin-converting enzyme (ACE) inhibitors who receive platelet transfusions through bedside leukoreduction filters. These curious reactions appear to involve dysmetabolism of the vasoactive substance bradykinin. Products contaminated by bacteria during blood collection and transfused can cause life-threatening septic reactions. A long-term complication of blood transfusion therapy unique to chronically transfused patients is iron overload. Less common - but serious - reactions more specific to blood transfusion include transfusion-associated graft-versus-host disease and transfusion-associated acute lung injury. Many of these complications of transfusion therapy can be prevented by adhering to well-established practice guidelines. In addition, individuals who administer blood transfusions should recognize these complications in order to be able to quickly provide appropriate treatment.

Very low platelet counts in post-transfusion purpura falsely diagnosed as heparin-induced thrombocytopenia. Report of four cases and review of literature

Differential diagnosis between post-transfusion purpura (PTP) and heparin-induced thrombocytopenia (HIT) can be difficult in the initial stages of thrombocytopenia, as the early clinical presentations are often similar. Four patients are described who were suspected clinically of suffering from HIT. All four patients had recent blood transfusions and platelet alloantibodies, thus the diagnosis of PTP was made. One lethal gastrointestinal and one retroperitoneal hemorrhage developed in two of the four patients. Unusually, one patient was male and two different platelet alloantibodies were present in his serum; in another patient platelet alloantibodies and HIT-antibodies were detectable. To arrive at the right diagnosis as quickly as possible is vitally important since treatment, which has to be initiated promptly, is very different for the two syndromes. Thus, we suggest that in patients where HIT is suspected, additional information should be sought. If features consistent with PTP (such as a recent blood transfusion or a marked drop in platelet count to below 15 Gpt/L) are present, we recommend parallel testing for platelet alloantibodies to rule out PTP.

Immune-mediated thrombocytopenias: basic and immunological aspects

Acute idiopathic or autoimmune thrombocytopenic purpura (AITP) is a disorder found mainly in children, usually preceded by a viral infection, with a higher incidence in the autumn and winter. The platelet-specific autoantibodies in acute childhood AITP are more often of the IgM class. Chronic AITP occurs mostly in adults. The platelet immunofluorescence test (PIFT) detects platelet-specific autoantibodies with a sensitivity of 65-75%. The autoantibodies in chronic AITP are classified as IgG in 95%, IgM in 26% and IgA in 4% of cases. The antibodies are usually bound to platelets and are detectable as free circulating antibodies in about 40%. AITP in pregnancy may cause neonatal AITP by autoantibodies of the IgG class which pass the placenta barrier. The rare neonatal alloimmune thrombocytopenic purpura (NAITP) are caused by IgG alloantibodies against HPA-1a in 75-90%, HPA1b in 3-5%, HPA 3a in 4-5%, HPA5b in 6-19% and against private platelet antigens in 3%. To confirm the diagnosis of NAITP requires extensive serological testing of the child, and the parents have to be typed for the important platelet-specific antigens by PIFT, monoclonal antibody immobilisation of platelet antigens (MAIPA) and/or enzyme-linked immunosorbent assay (ELISA) techniques. Three mechanisms of drug-induced thrombocytopenias are described. Platelets of both the donor and the patient are destroyed in post-transfusion thrombocytopenic purpura (PTP) but PTP does not occur again if incompatible platelets are re-administered.

Immunoglobulin G subclasses of anti-human platelet antigen 1a in maternal sera: relation to the severity of neonatal alloimmune thrombocytopenia

The monoclonal antibody immobilization of platelet antigen (MAIPA) technique was employed to detect and semiquantitatively assess total IgG anti-HPA-1a and its subclasses in sera of mothers who gave birth to severely thrombocytopenic (< 50 x 10(9) platelets/L)(n = 14) or mildly thrombocytopenic/unaffected (> 50 x 10(9) platelets/L)(n = 13) neonates. There was no statistically significant difference between the IgG anti-HPA-1a subclass composition of the 2 groups of sera. The majority of sera (26/27, 96%) showed IgG1 + IgG3 while 17/27 (63%) had all 4 subclasses of the antibody. No significant differences between the severely thrombocytopenic and mildly thrombocytopenic/unaffected groups were detected in the levels of IgG, IgG1, IgG2 or IgG4 of the antibody. However, the values of IgG3 anti-HPA-1a were significantly higher in the severely thrombocytopenic than in the mildly thrombocytopenic/unaffected group of sera with only little overlap (median 2.94 vs. 1.68, range 1.36-9.71 vs. 1.50-2.84, respectively; p < 0.01). The results suggest that maternal IgG3 anti-HPA-1a has predictive value for severe thrombocytopenia of the neonate. However, a prospective study of IgG HPA-1a subclasses in a greater number of maternal sera at different times of pregnancy is needed to test if IgG3 anti-HPA-1a is predictive of the degree of fetal/neonatal thrombocytopenia.