Increased risk of haematological malignancy in adults over age 60 with thrombocytopenia compared with matched controls: Time for an upfront bone marrow evaluation?

International societies have conflicting recommendations on whether bone marrow aspirate/biopsy (BMB) is needed during workup for isolated thrombocytopenia. Our objective was to determine if thrombocytopenia in patients aged ≥60 years is associated with an increased incidence of haematological malignancy. We performed a retrospective population-based cohort study in patients aged ≥60 years between January 1, 2009 to December 31, 2019. Exposed patients had specialist consultation for thrombocytopenia, with platelet count <100 × 109/L, but normal haemoglobin and white blood cell count. Unexposed patients were those who never had specialist consultation for thrombocytopenia and whose platelets were ≥100 × 109/L. The primary outcome was the diagnosis of haematological malignancy using a competing risk of death model. During 4.0 years (IQR 2.2-6.7) of follow-up, 378/4930 exposed (19.1/1000PY, 95% CI 17.1-21.0), and 204/17556 unexposed patients (2.5/1000PY, 95% CI 2.2-2.8) were diagnosed with haematological malignancy (HR 15.5 (95% CI 11.3-21.4, p < 0.0001) in year 1, and 5.3 (95% CI 4.4-6.6, p < 0.0001) in years 2+). This finding persisted in analyses stratified by sex, age, severity, or duration of thrombocytopenia, and treatment with corticosteroids within 2 weeks of consultation. This study found a strong association between isolated thrombocytopenia and haematological malignancy in patients ≥60 years, supporting consideration of diagnostic testing including BMB during outpatient specialist consultation.

ß-1 tubulin R307H SNP alters microtubule dynamics and affects severity of a hereditary thrombocytopenia.

BACKGROUND: Single nucleotide polymorphisms (SNPs) in platelet-associated genes partly explain inherent variability in platelet counts. Patients with monoallelic Bernard Soulier syndrome due to the Bolzano mutation (GPIBA A156V) have variable platelet counts despite a common mutation for unknown reasons. OBJECTIVES: We investigated the effect of the most common SNP (R307H) in the hematopoietic-specific tubulin isotype ß-1 in these Bernard Soulier patients and potential microtubule-based mechanisms of worsened thrombocytopenia. PATIENTS/METHODS: Ninety-four monoallelic Bolzano mutation patients were evaluated for the R307H ß-1 SNP and had platelet counts measured by three methods; the Q43P SNP was also evaluated. To investigate possible mechanisms underlying this association, we used molecular modeling of ß-1 tubulin with and without the R307H SNP. We transfected SNP or non-SNP ß-1 tubulin into MCF-7 and CMK cell lines and measured microtubule regrowth after nocodazole-induced depolymerization. RESULTS: We found that patients with at least one R307H SNP allele had significantly worse thrombocytopenia; manual platelet counting revealed a median platelet count of 124 in non-SNP patients and 76 in SNP patients (both ×10(9)  L(-1) ; P < 0.01). The Q43P SNP had no significant association with platelet count. Molecular modeling suggested a structural relationship between the R307H SNP and microtubule stability via alterations in the M-loop of ß tubulin; in vitro microtubule recovery assays revealed that cells transfected with R307H SNP ß-1 had significantly impaired microtubule recovery. CONCLUSIONS: Our data show that the R307H SNP is significantly associated with the degree of thrombocytopenia in congenital and acquired platelet disorders, and may affect platelets by altering microtubule behavior.

Decreased plasma cytokines are associated with low platelet counts in aplastic anemia and immune thrombocytopenic purpura.

BACKGROUND: We previously found plasma levels of CD40 ligand (CD40L), chemokine (C-X-C motif) ligand 5 (CXCL5), chemokine (C-C motif) ligand 5 (CCL5) and epidermal growth factor (EGF) to be low in aplastic anemia (AA) patients and to be correlated with platelet count. OBJECTIVES: To study the association of CD40L, CXCL5, CCL5 and EGF with platelets. METHODS: We measured cytokines in the plasma of immune thrombocytopenic purpura (ITP) and AA patients using the Luminex assay and confirmed the results in a mouse model and in vitro experiments. RESULTS: Both ITP and AA showed similarly low levels of CD40L, CXCL5, CCL5 and EGF, compared with healthy controls. In ITP, levels of these proteins were significantly greater in patients with higher platelet counts than in those with lower platelet counts. In a murine thrombocytopenia model, levels of CD40L, CXCL5, CCL5 and EGF decreased with platelet count after immune-mediated destruction, while the cytokine levels increased when the platelet count recovered. In vitro, concentrations of these cytokines in the supernatants of platelet suspensions were proportional to platelet numbers, and levels in sera prepared by simple blood coagulation were equivalent to those in platelet-rich plasma-converted sera. mRNA expression for CXCL5, CCL5 and EGF was higher in platelets than in megakaryocytes, peripheral blood mononuclear cells, granulocytes and non-megakaryocytic bone marrow cells. CONCLUSIONS: Plasma CD40L, CXCL5, CCL5 and EGF are mainly platelet-derived, suggesting a role of platelets in immune responses and inflammation. Measurement of CD40L, CXCL5, CCL5 and EGF in human blood allowed testable inferences concerning physiology and pathophysiology in quantitative platelet disorders.

Differences in platelet function in patients with acute myeloid leukemia and myelodysplasia compared to equally thrombocytopenic patients with immune thrombocytopenia.

BACKGROUND: Severe thrombocytopenia is a major risk factor for hemorrhage, but platelet function and bleeding risk at low platelet counts are poorly understood, because of the limitations of platelet function testing at very low platelet counts. OBJECTIVES: To examine and compare platelet function in severely thrombocytopenic patients with acute myeloid leukemia (AML) or myelodysplasia (MDS) with that in patients with immune thrombocytopenia (ITP). METHODS: Whole blood flow cytometric measurement of platelet activation and platelet reactivity to agonists was correlated with the immature platelet fraction (IPF) and bleeding symptoms. RESULTS: Patients with AML/MDS had smaller platelets, lower IPF and substantially lower platelet surface expression of activated glycoprotein (GP)IIb-IIIa and GPIb, both with and without addition of ex vivo ADP or thrombin receptor-activating peptide, than patients with ITP. In both ITP and AML/MDS patients, increased platelet surface GPIb on circulating platelets and expression of activated GPIIb-IIIa and GPIb on ex vivo activated platelets correlated with a higher IPF. Whereas platelet reactivity was higher for AML/MDS patients with bleeding than for those with no bleeding, platelet reactivity was lower for ITP patients with bleeding than for those with no bleeding. CONCLUSIONS: AML/MDS patients have lower in vivo platelet activation and ex vivo platelet reactivity than patients with ITP. The proportion of newly produced platelets correlates with the expression of platelet surface markers of activation. These differences might contribute to differences in bleeding tendency between AML/MDS and ITP patients. This study is the first to define differences in platelet function between AML/MDS patients and ITP patients with equivalent degrees of thrombocytopenia.

Prospective evaluation of a new platelet glycoprotein (GP)-specific assay (PakAuto) in the diagnosis of autoimmune thrombocytopenia (AITP).

Assays measuring platelet-associated immunoglobulin G (PAIgG), while highly sensitive, lack specificity in diagnosing autoimmune thrombocytopenia (AITP). We prospectively evaluated a new commercially available glycoprotein (GP)-specific assay, the PakAuto (GTI, Brookfield, WI), for its clinical usefulness in distinguishing immune from nonimmune thrombocytopenia (TP), in 216 patients with autoimmune TP (both primary "idiopathic" and "secondary") and 46 patients with TP due to other causes. This assay is designed to detect both platelet-associated (direct assay) and plasma (indirect assay) antiplatelet antibodies specific for GPs IIb/IIIa, Ib/IX, and Ia/IIa. The mean platelet counts of the immune (79 +/- 7 x 10(9)/L) and nonimmune groups (78 +/- 7 x 10(9)/L), were similar (P=0.95). The direct assay was positive in 114/216 patients with AITP (53%), and 13/46 with nonimmune TP (28%). Among the AITP group, the majority (61%) of patients with positive test results had autoantibodies reactive against all three GP targets. The sensitivity, specificity, positive, and negative predictive values for the direct PakAuto were 53%, 72%, 90%, and 24%, respectively, comparable to previously published experience of GP-specific assays. However, in some cases of TP due to nonimmune cause, the PakAuto was highly specific. Only 3 of 22 patients with gestational and 1 of 8 with familial/congenital TP had a positive direct assay, indicating that the test may be particularly useful for excluding an immune etiology for TP in certain patient subgroups.

Fetal and neonatal thrombopoietin levels in alloimmune thrombocytopenia.

Thrombopoietin (Tpo) is the main hematopoietic growth factor for platelet production. Plasma Tpo levels in autoimmune thrombocytopenic patients are normal or slightly elevated. Although thrombocytopenia exists, Tpo levels are not increased because the produced megakaryocytes and platelets can bind circulating Tpo, thereby normalizing Tpo levels. In this study, plasma samples from fetuses and neonates with neonatal alloimmune thrombocytopenia (NAIT), a different form of immune thrombocytopenia, were measured. Umbilical cord samples from 50 fetuses before treatment because of severe thrombocytopenia and 51 fetuses after treatment, and peripheral blood samples of 21 untreated newborns with NAIT were analyzed. As controls, plasma Tpo levels were determined in 21 umbilical cord samples of 14 nonthrombocytopenic fetuses with hemolytic disease resulting from red blood cell alloimmunization and in umbilical cord samples of 51 healthy newborns. The values were also compared with the plasma Tpo levels in 193 healthy adults. Mean Tpo levels from the groups of fetuses and neonates, including both NAIT and control plasma, were slightly but significantly elevated compared with levels in healthy adults. Tpo levels in NAIT samples were not significantly different from the levels in hemolytic disease samples or in samples from healthy newborns. Thus, as in autoimmune thrombocytopenic patients, normal Tpo levels are present in NAIT patients.

Novel approaches to refractory immune thrombocytopenic purpura.

Chronic immune thrombocytopenic purpura (ITP) is an organ-specific autoimmune bleeding disorder in which autoantibodies are directed against the individual's own platelets, resulting in increased Fc-mediated platelet destruction by macrophages in the reticuloendothelial system. Although ITP is primarily mediated by IgG autoantibodies, the production of these autoantibodies is regulated by the influence of T lymphocytes and antigen-presenting cells (APC). There is evidence that enhanced T-helper cell/APC interactions in patients with ITP may play an integral role in IgG antiplatelet autoantibody production. New therapies may improve platelet production, decrease platelet antibody production, and decrease monocyte function and/or B-cell and T-cell activities. Understanding these cellular immune responses in ITP may lead to the development of more specific immunoregulatory therapies for the management of this disease.

Anti-platelet antibodies associated with the Canale-Smith syndrome bind to the same platelet glycoprotein complexes as those of idiopathic thrombocytopenic purpura patients.

The Canale-Smith syndrome (CSS) is an inherited disease characterized by massive lymphadenopathy, hepatosplenomegaly and systemic autoimmunity to erythrocytes and platelets. Idiopathic thrombocytopenic purpura (ITP) is an autoimmune disease in which approximately 60-80% of patients have anti-platelet antibodies directed against specific platelet glycoprotein complexes (GPCs) located on their membrane: GP IIb/IIIa, GPIb/IX, and GPIa/IIa. Almost all (95-100%) of the antibody-positive patients have antibodies directed against GPIIb/IIIa alone, or in combination with other glycoprotein targets. Our objective was to determine the specificities of the anti-platelet antibodies in CSS patients. The detection of anti-platelet antibodies was performed using a commercially available ELISA, the Pak-AUTO (GTI, Brookfield, WI), in which highly purified GPIIb/IIIa, GPIb/IX, and GPIa/IIa are immobilized on microtitre plates, incubated with serum or plasma, and subsequently developed with an antihuman polyclonal immunoglobulin. Of 14 CSS patients tested, 11 (79%) had anti-platelet antibodies in their serum directed toward at least one of the three major GPC, nine (82%) of which were against GPIIb/IIIa alone or in combination. Antibodies detected in the sera of ITP patients had similar specificities. No such antibodies were detected in samples from 25 consecutive normal controls. These results demonstrate that a genetically defined defect in lymphocyte apoptosis results in a humoral autoimmune response with anti-platelet specificities very similar to the common idiopathic form of autoimmune thrombocytopenia.

Cytokine modulation with immune gamma-globulin in peripheral blood of normal children and its implications in Kawasaki disease treatment.

Intravenous immune gamma-globulin (IVIG) is used successfully in the treatment of Kawasaki disease, with dose-dependent rapid resolution of symptoms such as fever and irritability and a decrease in ESR, WBCs, and platelets. The mode of action of IVIG in reducing this inflammatory response is not clearly understood. Recently anticytokine antibodies in IVIG have been demonstrated. Serum levels of proinflammatory cytokines have been shown to be elevated in patients with Kawasaki disease. The cytokine interleukin-6 (IL-6) is involved in the de novo production of acute-phase proteins by hepatocytes and cause thrombocytosis and fever in response to tissue injury. Patients receiving parenteral recombinant human IL-6 have dose-dependently experienced fever, malaise, chills, and acute-phase reaction. With high IL-6 concentrations, central nervous system toxicity has also been reported and IL-6 has been thought to mediate endothelial damage. We evaluated the response of stimulated blood cells of 12 normal children to IVIG in the release of the cytokines IL-6, IL-8, TNF-alpha. and IL-6 receptor (sIL-6R). The levels of cytokines IL-6, IL-8, and TNF-alpha (but not sIL-6R) in peripheral blood induced by stimulation with LPS were markedly reduced (P < 0.008) within 3 hr when incubated with IVIG compared to without IVIG. Thus we demonstrated that cells of normal children respond to IVIG in vitro by reducing cytokines such as IL-8, TNF-alpha, and IL-6 without affecting the level of receptor sIL-6R during an acute inflammatory response. We also found significantly higher IL-6 levels in children with Kawasaki disease compared to children with blood culture-negative febrile illnesses. In five children with Kawasaki disease we measured serum IL-6 before and after IVIG and assessed the clinical response to IVIG therapy. Therapy with IVIG was followed by a rapid resolution of symptoms in Kawasaki disease, with a significant decrease in serum IL-6. The attenuation of proinflammatory cytokine responses, especially IL-6, following infusions of IVIG may play an integral role in the rapid resolution of symptoms and decrease in the acute-phase proteins in children with Kawasaki disease. Cells of normal children were found to respond to the IVIG in a manner similar to that of the Kawasaki children.

Functional properties of lymphocytes in idiopathic thrombocytopenic purpura.

Idiopathic or immune thrombocytopenic purpura (ITP) is characterized by antibody-mediated destruction of platelets. The etiology is unknown. We postulated that increased autoantibody production in ITP might be attributable to either increased or prolonged expression of CD40 ligand (CD40L, CD154) in T or B lymphocytes, as has been previously observed in systemic lupus erythematosus (SLE). In addition, we hypothesized that ITP is characterized by increased levels of interleukin 4 (IL-4), a prototypic Th2 cytokine which, along with CD40 ligation, is required for B cell differentiation and production of several IgG subclasses. Cell surface CD154 expression was measured in freshly-isolated and in vitro-activated peripheral blood lymphocytes of sixteen ITP patients and eight healthy volunteers. Plasma levels of IL-4 and the prototypic Th1 cytokine interferon-gamma (IFNgamma) were determined. We observed that CD154 expression in unstimulated and in vitro-activated lymphocytes did not differ between ITP patients and healthy controls. Plasma levels of the Th2 cytokine IL-4 were significantly higher in the ITP patients. These studies indicate that overexpression of CD154 in lymphocytes is unlikely to be a primary pathophysiological defect in most patients with ITP. The data support that in addition to cell membrane antigens such as CD154, soluble cytokines such as IL-4 should be considered as potential targets for therapy in this disease.

Spontaneous remission of congenital acute nonlymphoblastic leukemia with normal karyotype in twins.

BACKGROUND: Congenital acute nonlymphoblastic leukemia (cANLL) is an extremely rare event and represents only 0.5-1% of the leukemias in the first year of life. It is usually more common among patients with chromosomal abnormalities. Transient myeloproliferative disease (TMD) is an hyperleukocytosis entity that occurs almost exclusively in Down syndrome patients and remits spontaneously. Spontaneous remission of congenital leukemia has been reported and related to the presence of an extra chromosome 21. PROCEDURE: A pair of non-Down syndrome newborn twins presented with a clinical picture of skin rash and hyperleukocytosis. Twin B had full-blown cANLL with bone marrow, peripheral blood, skin, CSF, and placental invasion. Twin A presented transient peripheral blood and skin involvement by the same type of blast cells. No cytotoxic therapy was given. With 2 years follow-up, they continue to do well. RESULTS: Histologic and immunophenotypical analysis of placentas, cord blood, skin, CSF, bone marrows, and peripheral blood revealed a consistent picture of intrautero cANLL in twin B, with transplacental invasion of twin A. Normal and blast cells were found to be karyotypically normal. Spontaneous remission occurred. CONCLUSIONS: cANLL with karyotypically normal blasts can develop a self-limited clinical course, which has resemblances to TMD.

Serum granulocyte colony-stimulating factor levels are not increased in patients with autoimmune neutropenia of infancy.

OBJECTIVE: To assess the role of granulocyte colony-stimulating factor (G-CSF) in autoimmune neutropenia (AIN). DESIGN: Serum G-CSF levels were measured in 57 children with AIN. Two different G-CSF-dependent assays were used: a solid-phase "sandwich" enzyme-linked immunosorbent assay and a proliferation assay. Sera from healthy persons and from patients with severe congenital neutropenia were used for negative and positive controls. RESULTS: The median G-CSF level in healthy persons (n = 13) was low, 45.6 pg/mL (range <39 to 141 pg/mL). The median G-CSF level in patients with AIN (n = 57) was very similar, 45.5 pg/mL (range <39 to 2500 pg/mL). Forty-five (79%) of 57 patients with AIN had levels within the range of the control group. Seven (12%) had marginally increased G-CSF levels (141 to 400 pg/mL), and only 5 (9%) had levels higher than 400 pg/mL. The G-CSF levels measured by enzyme-linked immunosorbent assay correlated well with levels measured by the proliferation assay, thus demonstrating that antibodies present in patient sera did not affect the biologic activity of G-CSF. CONCLUSION: G-CSF production in AIN is not increased despite the low neutrophil count, similar to thrombopoietin in immune thrombocytopenic purpura.

Thrombocytopenia with absent radii: frequency of marrow megakaryocyte progenitors, proliferative characteristics, and megakaryocyte growth and development factor responsiveness.

Congenital thrombocytopenia with absent radii (TAR syndrome) is characterized by defective thrombopoiesis and bleeding in early infancy. To determine the frequency and responsiveness to cytokines of megakaryocyte progenitors (CFU-Meg) in TAR syndrome, the authors studied marrow samples from 3 patients and 6 normal controls, using optimally standardized megakaryocyte growth media incorporating interleukin-3, interleukin-6, stem cell factor, and granulocyte-monocyte colony-stimulating factor, with and without pegylated recombinant human megakaryocyte growth and development factor (PEG-rHuMGDF). CFU-Meg was identified with a specific staining system utilizing monoclonal antibodies to glycoprotein IIb/IIIa. Growth of small CFU-Meg colonies (3-20 cells/colony) was observed in all patients in cultures without PEG-rHuMGDF, with a mean frequency of 8 (range 5-12) per 2.25 x 10(5) mononuclear cells plated (control mean 23; range 2-70). Identical cultures of marrow cells from patients and controls with added PEG-rHuMGDF produced more colonies per dish (mean 17, range 8-23; control mean 30, range 6-62). Except for 1 case, however, patients' colonies in response to PEG-rHuMGDF remained smaller than those of controls. Two patients tested had higher plasma thrombopoietin levels than 6 normal subjects. The findings demonstrate proliferative and PEG-rHuMGDF-responsive megakaryocytic progenitors in TAR syndrome. The modest reduction in frequency of megakaryocyte progenitors and the suboptimal size of colonies in response to PEG-rHuMGDF are compatible with the reported defective signal transduction in the c-mpl pathway in TAR syndrome.

Hematologic toxicity of sodium valproate.

PURPOSE: Sodium valproate is a commonly used anticonvulsant in the management of childhood refractory epilepsy with good response rates and acceptable toxicity. Hepatotoxicity is the most widely recognized toxicity. With the use of higher drug levels to achieve adequate seizure control, hematologic toxicity is being increasingly encountered, and the pediatric hematologist is consulted for these problems in the pre- or perioperative setting. The purpose of this article is to characterize the various hematologic toxicities encountered in a clinical setting and to provide guidelines to assist in the management of these patients. METHODS: A literature review was undertaken to identify the hematologic toxicities of valproate used as monotherapy or polytherapy. Key words used in the search were valproate, hematology, and bleeding. RESULTS: Valproate can cause direct bone marrow suppression leading to aplastic anemia or peripheral cytopenia affecting one or more cell lines. Occasional fatal bone marrow failure, myelodysplasia, and a clinical picture resembling acute promyelocytic leukemia have also been seen. Thrombocytopenia, macrocytosis, neutropenia, and pure red cell aplasia can occur but are not reported to be life-threatening. A bleeding diathesis associated with valproate use may include thrombocytopenia, abnormal platelet function, and acquired von Willebrand disease type I. CONCLUSIONS: Hematologic toxicities of valproate are common, vary in onset and severity, are recurrent, transient, or persistent, and usually occur with a serum valproate level greater than 100 microg/mL. In most situations, even when highly clinically significant, they can be reversed with dosage reduction; drug discontinuation is rarely required. Potential adverse effects such as thrombocytopenia and leukopenia are easily detected by laboratory monitoring, which should be continued indefinitely at least on a quarterly basis. Caution for elective surgery is advised; preoperative coagulation studies should be done, including platelet function studies and von Willebrand factor levels. Perioperative use of DDAVP to increase von Willebrand factor levels and improve platelet function is appropriate in some cases.

Overview of idiopathic thrombocytopenic purpura: new approach to refractory patients.

Idiopathic thrombocytopenic purpura is a disorder in which autoantibodies are made to platelets, resulting in accelerated platelet destruction. The diagnosis may be made in outpatients who are previously well or in patients with multiple medical conditions and medications. There are no unequivocal ways to distinguish immune thrombocytopenias from other thrombocytopenias, even with state-of-the-art tests including anti-platelet antibodies, thrombopoietin, glycocalicin, and platelet reticulocyte counts. Clinical evaluation includes ruling out a systemic process such as a viral infection or leukemia. Treatment of idiopathic thrombocytopenic purpura should be individualized. Substantial platelet increases are seen in more than 50% of patients who receive intravenous IgG, intravenous anti-D, steroids, or splenectomy. Two additional agents showing promising clinical trial experience are anti-CD40 ligand and rituximab (Rituxan; Genentech, Inc, South San Francisco, CA and IDEC Pharmaceutical Corporation, San Diego, CA).

Is it necessary to test patients with immune thrombocytopenic purpura (ITP) for seropositivity to HTLV-1?

HTLV-111 (HIV-1) has been shown to be associated with thrombocytopenia of a type resembling immune thrombocytopenic purpura (ITP). HTLV-1 is a retrovirus similar to HIV-I (HTLV-III) in a number of features, such as CD4 tropism. It is responsible for several clinical entities, including adult T-cell leukemia/lymphoma. The relationship, if any, of HTLV-1 and thrombocytopenia has not been systematically studied. To determine how frequently ITP patients are commonly infected with HTLV-1, the following study was performed. Frozen serum samples from 123 randomly selected patients with ITP were thawed and tested for antibodies to HTLV-1 by enzyme-linked immunoabsorbent assay. Positives were confirmed by Western blot. Three patients were initially found to be positive for HTLV-1. One was a female of Caribbean ancestry, one was a male HIV-1+ patient, and one was an adolescent female with no known risk factors for HIV-1. The two females later tested negative for HTLV-1. As a screening program for HTLV-1 antibodies was not introduced into blood banks until November 1988, there may have been passive transfer of the virus from intravenous immunoglobulin that these patients had received. This study of a large number of ITP patients shows that it is extremely unlikely that they are infected with HTLV-1, and, therefore, it is unnecessary to screen ITP patients for seropositivity to HTLV-1.

BRa (HPA-5b) incompatibility may cause thrombocytopenia in neonates of mothers with immune thrombocytopenic purpura.

PURPOSE: The association of anti-Br(a) immunoglobulin G (IgG) platelet alloantibodies with the development of thrombocytopenia in neonates of mothers with autoimmune thrombocytopenic purpura (ITP) is reported. METHODS: Between March 1994 and July 1997, 28 consecutive pregnant women with ITP seen at New York Hospital were screened for platelet-reactive antiglycoprotein (glycoprotein [GP] IIb/IIIa, Ib/IX, and Ia/IIa) antibodies. RESULTS: The sera from 6 of these 28 women contained IgG alloantibodies to GP Ia/IIa directed against the Br(a) (HPA-5b) antigen. Only three families each had at least one Br(a)+ and at least one Br(a)- infant. Platelet typing in these families revealed that the mothers were Br(b/b) (Br(a)-) and the fathers were Br(a/b) (Br(a)+). Platelet counts < 100,000/microl occurred only in 2 of the 3 infants who were Br(a)+. The platelet counts were significantly lower in the three Bra+ infants compared to the five Br(a)- infants (p = 0.038). CONCLUSION: Platelet alloimmunization with anti-Br(a) can cause neonatal thrombocytopenia in infants of mothers with ITP. Platelet antibody testing in the pregnant women with ITP is recommended.