Detection of drug-dependent antibodies by the 51Cr platelet lysis test: documentation of immune thrombocytopenia induced by diphenylhydantoin, diazepam, and sulfisoxazole

Approach to the diagnosis and management of drug-induced immune thrombocytopenia

Drug-induced immune thrombocytopenia (DITP) is a challenging clinical problem that is under-recognized, difficult to diagnose and associated with severe bleeding complications. DITP may be caused by classic drug-dependent platelet antibodies (eg, quinine); haptens (eg, penicillin); fiban-dependent antibodies (eg, tirofiban); monoclonal antibodies (eg, abciximab); autoantibody formation (eg, gold); and immune complex formation (eg, heparin). A thorough clinical history is essential in establishing the diagnosis of DITP and should include exposures to prescription medications, herbal preparations and even certain foods and beverages. Clinical and laboratory criteria have been established to determine the likelihood of a drug being the cause of thrombocytopenia, but these criteria can only be applied retrospectively. The most commonly implicated drugs include quinine, quinidine, trimethoprim/sulfamethoxazole and vancomycin. We propose a practical approach to the diagnosis of the patient with suspected DITP. Key features are: the presence of severe thrombocytopenia (platelet nadir <20×10(9)/L); bleeding complications; onset 5 to 10days after first drug exposure, or within hours of subsequent exposures or after first exposure to fibans or abciximab; and exposure to drugs that have been previously implicated in DITP reactions. Treatment involves stopping the drug(s), administering platelet transfusions or other therapies if bleeding is present and counselling on future drug avoidance. The diagnosis can be confirmed by a positive drug re-challenge, which is often impractical, or by demonstrating drug-dependent platelet reactive antibodies in vitro. Current test methods, which are mostly flow cytometry-based, must show drug-dependence, immunoglobulin binding, platelet specificity and ideally should be reproducible across laboratories. Improved standardization and accessibility of laboratory testing should be a focus of future research.

Drug-induced immune thrombocytopenia

Thrombocytopenia is caused by immune reactions elicited by diverse drugs in clinical practice. The activity of the drug-dependent antibodies produces a marked decrease in blood platelets and a risk of serious bleeding. Understanding of the cellular mechanisms that drive drug-induced thrombocytopenia has advanced recently but there is still a need for improved laboratory tests and treatment options. This article provides an overview of the different types of drug-induced thrombocytopenia, discusses potential pathologic mechanisms, and considers diagnostic methods and treatment options.

A systematic evaluation of laboratory testing for drug-induced immune thrombocytopenia

BACKGROUND

Drug-induced immune thrombocytopenia (DITP) can be confirmed by the demonstration of drug-dependent platelet antibodies in vitro; however, laboratory testing is not readily accessible and test methods are not standardized.

OBJECTIVE

To identify drugs with the strongest evidence for causing DITP based on clinical and laboratory criteria.

PATIENTS/METHODS

We developed a grading system to evaluate the quality of DITP laboratory testing. The 'DITP criteria' were: (i) Drug (or metabolite) was required for the reaction in vitro; (ii) Immunoglobulin binding was demonstrated; (iii) Two or more laboratories obtained positive results; and (iv) Platelets were the target of immunoglobulin binding. Laboratory diagnosis of DITP was considered definite when all criteria were met and probable when positive results were reported by only one laboratory. Two authors applied the DITP criteria to published reports of each drug identified by systematic review. Discrepancies were independently adjudicated.

RESULTS

Of 153 drugs that were clinically implicated in thrombocytopenic reactions, 72 (47%) were associated with positive laboratory testing. Of those, 16 drugs met criteria for a definite laboratory diagnosis of DITP and thus had the highest probability of causing DITP. Definite drugs were: quinine, quinidine, trimethoprim/sulfamethoxazole, vancomycin, penicillin, rifampin, carbamazepine, ceftriaxone, ibuprofen, mirtazapine, oxaliplatin and suramin; the glycoprotein IIbIIIa inhibitors abciximab, tirofiban and eptifibatide; and heparin.

CONCLUSIONS

We identified drugs with the strongest evidence for an association with immune thrombocytopenia. This list may be helpful for ranking potential causes of thrombocytopenia in a given patient.

Drug-induced thrombocytopenia in critically ill patients

Thrombocytopenia occurs in 15% to 58% of intensive care unit patients. The incidence varies based upon patient population, timing and frequency of platelet monitoring, and definition of thrombocytopenia. Up to 25% of acutely ill patients develop drug-induced thrombocytopenia. When drug-induced thrombocytopenia is suspected, nondrug related causes must be evaluated and excluded. Establishing the diagnosis of drug-induced thrombocytopenia is challenging, as hundreds of medications have been implicated. Medications commonly associated with drug-induced thrombocytopenia include glycoprotein IIb/IIIa inhibitors, cinchona alkaloids, antibiotics, anticonvulsants, and heparin. Once the diagnosis is suspected, clinicians should identify the start date of medications to assess the timeline of development. The likelihood of each medication causing thrombocytopenia must be evaluated. The risk vs. benefit of discontinuing the suspected medication and availability of alternative medications must be assessed. The role of corticosteroids, immune globulin, and plasmapheresis is uncertain. Once the offending agent has been discontinued, the overall prognosis is excellent. In the case of suspected or confirmed heparin-induced thrombocytopenia, an alternative anticoagulant should be initiated. Drug-induced thrombocytopenia should be documented in the medical record and reported according to institutional and national standards. This review focuses on immune-mediated drug-induced thrombocytopenia from medications commonly utilized in the critically ill patient.

Drug-induced immune thrombocytopenia: pathogenesis, diagnosis, and management

Drug-induced immune thrombocytopenia (DITP) can be triggered by a wide range of medications. Although many cases of DITP are mild, some are characterized by life-threatening bleeding symptoms. The pathogenesis of DITP is complex, in that at least six different mechanisms have been proposed by which drug-induced antibodies can promote platelet destruction. It is possible in many cases to identify antibodies that react with platelets in the presence of the sensitizing drug, but the required testing is technically demanding and not widely available. Therefore, a decision on whether to discontinue an implicated medication in a patient suspected of having DITP must be made on clinical grounds. An algorithm is available that can be helpful in assessing the likelihood that a particular drug caused thrombocytopenia, but the most important aspects of patient management are a high index of suspicion and a careful history of drug exposure in an individual who presents with acute, often severe thrombocytopenia of unknown etiology. How drugs induce platelet-reactive antibodies and how, once formed, the antibodies cause platelet destruction following exposure to the drug is poorly understood. Further studies to address these issues and characterize more completely the range of drugs and drug metabolites that can cause DITP are needed.

Association of drug-serum protein adducts and anti-drug antibodies in dogs with sulphonamide hypersensitivity: A naturally occurring model of idiosyncratic drug toxicity

BACKGROUND

Sulphonamide antimicrobials, such as sulphamethoxazole (SMX), provide effective infection prophylaxis in immunocompromised patients, but can lead to drug hypersensitivity (HS) reactions. These reactions also occur in dogs, with a similar time course and clinical presentation as seen in humans.

OBJECTIVES

Drug-serum adducts and anti-drug antibodies have been identified in sulphonamide HS humans. The aim of this study was to determine whether similar markers were present in dogs with sulphonamide HS.

METHODS

Thirty-four privately owned sulphonamide HS dogs, 10 sulphonamide-'tolerant' dogs, 18 sulphonamide-naïve dogs, and four dogs experimentally dosed with SMX and the oxidative metabolite SMX-nitroso, were tested for drug-serum adducts by immunoblotting, and anti-drug antibodies by ELISA.

RESULTS

Sulphonamide-serum adducts were found in 10/20 HS dogs tested (50%), but in no tolerant dogs. Anti-sulphonamide IgG antibodies were detected in 17/34 HS dogs (50%), but in only one tolerant dog; antibody absorbance values were significantly higher in HS dogs. There was a significant association between the presence of sulphonamide-serum adducts and anti-sulphonamide antibodies (P = 0.009). Anti-drug antibodies were also found in dogs experimentally dosed with SMX-nitroso followed by SMX, but not in a dog dosed with drug vehicle, followed by SMX.

CONCLUSION

Similar humoral markers are present in dogs and humans with sulphonamide HS, supporting the use of dogs as a naturally occurring model for this syndrome in humans. These data suggest the potential use of drug-serum adducts and anti-drug antibodies as markers for sulphonamide HS. Preliminary data indicate that anti-sulphonamide antibodies may be triggered by the SMX-nitroso metabolite, not by the parent drug, in dogs.

Glycoprotein IIb/IIIa complex is the target in mirtazapine-induced immune thrombocytopenia

Mirtazapine (MW 265.36), a tetracyclic antidepressant of the piperazine-azapine group which augments central noradrenergic and serotonergic activity, is currently used as an oral antidepressant. We report a case of severe thrombocytopenia in a 66-year-old patient occurring after mirtazapine administration, suggesting an immune mechanism. This report documents the first case of mirtazapine-induced immune thrombocytopenia. The patient's serum was screened for drug-induced anti-platelet antibody with the chromium(51) (Cr(51)) platelet lysis technique. The drug-dependent antibody was characterized using flow cytometry, the monoclonal antibody immobilization of platelet antigens assay (MAIPA assay), and immunoprecipitation. By the Cr(51) platelet lysis technique, we obtained an equivocal result for the detection of mirtazapine-induced antibody. However, the patient's serum tested positive for mirtazapine-induced antibody by flow cytometry. The results showed that the binding ratio of 5.7 (mean fluorescence intensity) in the presence of the patient's serum and mirtazapine in a final concentration of 1.0 mmol/L was strongly positive. The antibody was found to bind the glycoprotein (GP) IIb/IIIa complex by MAIPA assay by using five different monoclonal antibodies against GP complexes Ib/IX, GPIIb/IIIa, or GPIa/IIa. Immunoprecipitation studies showed that the GPIIb/IIIa complex was precipitated by antibody in the presence, but not in the absence, of mirtazapine. These findings provide evidence that immune thrombocytopenia can be caused by sensitivity to the antidepressant mirtazapine. This is the first well-documented case of mirtazapine-induced immune thrombocytopenia.

The laboratory diagnosis of platelet disorders

OBJECTIVE

To provide both a detailed description of the laboratory tests available in the diagnosis of platelet disorders and a testing algorithm, based on platelet count, that can be used to direct the evaluation of platelet disorders.

DATA SOURCES

A literature search was conducted using the National Library of Medicine database.

STUDY SELECTION

The literature on laboratory testing of platelet function was reviewed.

DATA EXTRACTION AND DATA SYNTHESIS

Based on the literature review, an algorithm for platelet testing was developed.

CONCLUSIONS

A history of mucocutaneous bleeding often indicates abnormal platelet function that can be associated with a normal, increased, or decreased platelet count. Multiple laboratory procedures can now be used to determine the underlying pathologic condition of platelet dysfunction when other deficiencies or defects of the coagulation cascade or fibrinolysis are ruled out. Simple procedures, such as platelet count, peripheral blood smear, and a platelet function screening test, will often lead the investigator to more specific analyses. Although platelet function testing is often limited to larger medical centers with highly trained technologists, newer technologies are being developed to simplify current procedures and make platelet function testing more accessible. This review provides an algorithm for platelet testing that may be of benefit to pathologists and physicians who deal with hemostatic disorders.

Stevens-Johnson syndrome in a patient receiving anticonvulsant therapy during cranial irradiation

A 28-year-old female patient with a recent history of breast carcinoma was referred to our clinic with generalized necrotic skin eruptions and severe mucosal erosions, which developed right after the completion of cranial radiotherapy for brain metastases. She had been receiving prophylactic diphenylhydantoin treatment 100 mg three times daily during radiation therapy. The extensive involvement of the oral mucosa with conjunctivitis and synechiae of the eyelids, facial swelling, and extension of the rash over the trunk and shoulders with bullous detachment of less than 10% of the total body surface strongly suggested Stevens-Johnson syndrome caused by phenytoin treatment in our patient. There has been conflicting evidence on the role of radiotherapy in the increased risk of severe drug reactions. Although various authors have emphasized the augmented rate of severe mucocutaneous reactions caused by anticonvulsants given during radiotherapy and suggested discontinuing the prophylactic use of such drugs in patients with no history of seizures, others have argued in favor of prophylactic anticonvulsants. Given the high risk of seizures, reaching 20% in patients with brain tumors, and the low incidence of drug reactions, the suggestion of refraining from prophylactic anticonvulsants in the setting of primary or metastatic brain tumors is controversial.

Hematologic side effects of psychotropics

Psychiatrists are often unaware of the potential hematologic complications of the psychotropics they prescribe. Although this review is not a hematologic text reference, relevant hematologic syndromes are described so that the consultation-liaison psychiatrist will be familiar with the usual signs, symptoms, and treatments of these syndromes. This article reviews the hematologic side effects of the commonly prescribed psychotropics, including antipsychotics, antidepressants, benzodiazepines, lithium, mood stabilizers (including some of the anticonvulsants), and the acetylcholinesterase inhibitors. Clinical signs and symptoms that should alert the physician to obtain a complete blood count are described.

Phenytoin-associated thrombocytopenia in a toddler

Hematologic side effects are rare side effects of treatment with phenytoin. We report a 2-year-old girl who developed reversible thrombocytopenia following treatment with phenytoin. Thrombocytopenia as a side effect of phenytoin treatment has usually been reported in adults and generally occurs 2 to 4 weeks after initiation of therapy. In our case, the thrombocytopenia developed on the 11th day of therapy and resolved 5 days after discontinuation of the phenytoin.

Phenytoin-induced thrombocytopenia

OBJECTIVE

To describe a patient with severe thrombocytopenia induced by the administration of phenytoin for prevention of seizures. A review of the literature supplements this case description to alert clinicians to this potentially serious hematologic reaction.

CASE SUMMARY

A woman who had experienced two seizures was prescribed phenytoin to prevent seizure recurrence. Further evaluation revealed a tumor, which was resected, and phenytoin was continued. Thrombocytopenia was noted 15 days after initiation of phenytoin, which was replaced with phenobarbital. Platelet transfusion and administration of intravenous immune globulin were used to treat her thrombocytopenia. Platelets were within the normal range by day 8 after the operation.

DISCUSSION

Phenytoin has been reported to induce various hematologic reactions, including thrombocytopenia. An intermediate epoxide metabolite of phenytoin is suspected as the cause of platelet destruction, which may occur via a complement-antibody reaction. Our patient experienced some confusion as a possible consequence of her thrombocytopenia, but no long-term sequelae followed.

CONCLUSIONS

Due to widespread use of phenytoin, clinicians must recognize the potential for the rare but serious adverse effect of thrombocytopenia, particularly in the neurosurgical population. Confusion, as observed in our patient, makes postoperative evaluation of central nervous system and cognitive function difficult, and can obscure the clinical presentation. At its worst extreme, disruption of platelet function may produce cerebral hemorrhage, which results in long-term functional deficits.

Thrombocytopenia following administration of phenytoin, dexamethasone and cimetidine: a case report and a potential mechanism

Cimetidine and phenytoin are useful medications often used together in patients with seizure disorders secondary to brain masses or metabolic abnormalities. We describe a case of thrombocytopenia in the setting of concurrent phenytoin, dexamethasone and cimetidine administration, and compare it with previously described cases of thrombocytopenia induced by concurrent use of phenytoin, cimetidine, and glucocorticoids. The similarities between these cases suggest mechanisms by which these agents may induce thrombocytopenia, specifically through potential downregulation of epoxide hydrolase by glucocorticoids.

Quinine-induced disseminated intravascular coagulation

Recurrent disseminated intravascular coagulation occurred in 3 women after ingestion of quinine tablets for cramp. All had circulating quinine-dependent antibodies to platelets and in 2 there was initial evidence of antibody consumption, with low titres that rose steeply over the next few days and remained high for many months.

Immunopathology of childhood idiopathic thrombocytopenic purpura

Modern laboratory techniques have begun to elucidate the pathophysiology of chronic childhood ITP. Quantitative assays of PAIgG, complement, immune complexes, and platelet kinetic studies have all provided important information. Chronic ITP of childhood appears to be similar to adult ITP, with production of an antibody directed against platelets and megakaryocytes. Most of the antibody is produced in the spleen, but other parts of the RES can also produce antibody. Complement, immune complexes, and cell-mediated immunity may play a role in the pathogenesis. Sensitized platelets are cleared by the RES, particularly in the spleen. Platelet kinetic studies show that platelet turnover is usually rapid with compensatory increased thrombopoiesis, but there are some patients who have decreased thrombopoiesis. Acute ITP of childhood is a brief illness, characterized by abrupt onset of hemorrhagic symptoms and complete recovery. It often follows a viral illness, suggesting that immune complexes as well as antibodies are important in the pathogenesis. Both the spleen and liver may be important organs of immune clearance.

The effect of lithium on platelet count

The effect of lithium on platelet count was studied by examining 12 patients treated with lithium carbonate without any additional medication, 13 patients treated with lithium carbonate with additional psychotropic medication, 25 patients with major affective disorder prior to any treatment, 25 patients with panic disorder prior to any treatment and 25 healthy controls. The platelet counts were increased in the group of subjects treated with lithium carbonate without any additional psychotropic medication. The increase was not clinically significant.

A naturally occurring, warm-reactive macroglobulin specific for papain-treated human platelets: preliminary characterization

Sera from 28 of the 113 normal children and adults (25%) studied were found to contain an immunoglobulin capable of causing complement-dependent lysis of normal platelets treated with small quantities of papain. This factor reacts equally well at 4 degrees C and at 37 degrees C with a determinant induced on platelets from normal subjects by treatment with papain or bromelain, but not by trypsin, chymotrypsin, or neuraminidase. It does not bind to red cells treated with any of these enzymes. The site(s) for which the factor was specific could not be induced on platelets from six patients with type I Glanzmann's thrombasthenia (lacking glycoproteins IIb and IIIa), in contrast to platelets from each of 20 normal donors. Isolation and characterization of the factor has been difficult because of its intolerance to chemical and physical manipulation. In 11 of the 20 individuals studied, however, it was found to have the properties of an IgM immunoglobulin. The factor appears to be different from any previously described, naturally occurring human immunoglobulin. It has not yet been shown to be associated with any disease state, but in the presence of complement, it is capable of causing profound damage to platelets previously subjected to minimal proteolysis, and the possibility that it can provoke platelet destruction in some conditions deserves further study.

Severe thrombocytopenia associated with phenytoin and cimetidine therapy

A 67-year-old man developed a sudden onset of severe isolated thrombocytopenia (platelet count, 1000/mm3) after 10 days of phenytoin administration as a prophylactic measure prior to craniotomy. The patient had also been taking cimetidine for 2 months prior to admission. No other hematological complications were noted, and an extensive hematologic investigation was otherwise unremarkable. Rapid resolution of the thrombocytopenia upon discontinuation of phenytoin and cimetidine strongly suggests a drug-induced adverse reaction.

Neonatal isoimmune thrombocytopenia. The natural course and management and the detection of maternal antibody

Isoimmune neonatal thrombocytopenia purpura (INTP) is a disease caused by platelet destruction by maternally derived antibody. Six patients were investigated. Maternal derived platelet transfusions in two patients resulted in posttransfusion platelet counts of greater than 85,000/microliter, a normal platelet survival of 7 to 10 days, and an early discharge from the hospital. In four patients, random donor platelet transfusions administered in the first week caused a transient rise of between 7 and 30,000 platelets per microliter with a return to pretransfusion levels 24 to 48 hours later, confirming the ineffectiveness of this form of treatment. Corticosteroid therapy is not effective and because of its potential toxicity should not be recommended for use in INTP. Platelet antigen was identified in the parents, and maternal sensitization was proven by the presence of platelet specific antibody. Severity of the disorder was estimated by the initial platelet count and the duration in weeks for the platelet count to rise above 100,000/microliter. Lymphocytotoxicity and immune lysis, as measured by the 51Chromium release assay, did not show an obvious relationship with the severity of the disorder. In our patients, high scores in the platelet suspension immunofluorescence test related to a more severe disorder, but a larger series would be necessary to confirm this finding.

Immune thrombocytopenia associated with tuberculosis

Thrombocytopenia associated with Mycobacterium tuberculosis infection developed concurrently in a mother and son. Antiplatelet antibodies were demonstrated in the serum of both patients. It is suggested that this and possibly other hematologic complications associated with tuberculosis are immune mediated.

Post-transfusion purpura: a serological and immunochemical study

By applying the platelet suspension immunofluorescence test (PSIFT), platelet-specific alloantibodies responsible for post-transfusion purpura were detected in eight patients within a period of 2 years. All patients were female and had previously received blood or had been pregnant. The platelet-specific alloantibodies had the specificity anti-Zwa in all the patients, who were all Aw(a-). In two patients the platelets were tested in the acute phase of the disease and found to be coated with IgG. In one patient an ether eluate was prepared from the platelets that reacted strongly with Zw(a+) platelets, but weakly with platelets from Zwb-homozygous individuals. The sera of these two patients, and of two others whose platelets were not directly tested, taken in the acute phase of the purpura, reacted strongly with Zwa-positive platelets. The four sera also reacted, however weakly, with Zwa-negative platelets, with autologous platelets taken during remission and with platelets from patients with Glanzmann's disease. It is postulated that Zwa-anti-Zwa complexes, present in the eluate and the sera, caused the reaction with Zwa-negative platelets and the patients' own platelets. Immunochemical characterization of the post-transfusion purpura antibodies showed that in all patients these were IgG, in two combined with IgM antibodies. Antibodies of the sub-class IgG1 were found in all patients, sometimes together with IgG3. In the indirect immunofluorescence test with anti-complement serum, the PTP antibodies in only four sera were able to fix complement. In only two of these sera were these complement-binding antibodies detectable in the 51 Cr-lysis technique and then in a much lower titre than in the immunofluorescence technique.

Bernard-Soulier disease: a study of four patients and their parents

Two families with Bernard-Soulier disease, including four patients and three of their parents, were studied and detailed clinical summaries are presented. One patient in each family has suffered severe bleeding problems while the other affected sibling is less severely affected. There has been no excessive bleeding in any of the parents or other family members. The patients demonstrated the abnormalities characteristic for Bernard-Soulier disease: thrombocytopenia, giant platelets, prolonged bleeding time, abnormal platelet aggregation to human FVIIIvWF and ristocetin or bovine FVIIIvWF alone, defective ristocetin-induced binding of human 125I-FVIIIvWF multimers, decreased platelet lysis by a drug-dependent antibody and complement, and a decreased concentration of membrane glycoprotein I. The parents had normal platelet counts, bleeding times, and FVIII-mediated aggregation. However, the parents had abnormally large platelets decreased sensitivity to lysis by a drug-dependent antibody and complement, and a decreased concentration of membrane glycoprotein I. Therefore the heterozygous state for Bernard-Soulier disease is recognizable by platelet membrane abnormalities although there is no defect of platelet function and no excessive bleeding. Red cell membrane proteins of one patient were normal, suggesting that phenotypic expression of the Bernard-Soulier disease defect is restricted to platelets.

Detection of platelet antibodies by enzyme-linked immunosorbent assay (ELISA) on artificial monolayers of platelets

For the detection of platelet antibodies we developed an enzyme-linked immunosorbent assay (ELISA) on artificial monolayers of platelets in wells of micro-titre-U-trays. This simple and reproducible test can not only detect the presence and the specificity of platelet antibodies but also the class and subclass of the antibodies involved.

Immune thrombocytopenia in severe neonatal infections

Thrombocytopenia occurs frequently in newborn infants with sepsis, but the exact mechanism remains obscure in those infants who do not have evidence of disseminated intravascular coagulation. Since recent work has suggested a possible immune mechanism for thrombocytopenia observed in adults with sepsis, we have investigated the role of platelet-associated immunoglobulin in severe neonatal infections. To detect PAIgG we use a method employing protein A and peroxidase-antiperoxidase as a labeled antibody. PAIgG was quantitated by phase contrast microscopy and expressed as a reactive index. Our control group included 16 normal newborn infants whose mean RI was 0.65 +/- 0.01 SE. In addition to the control group, five infants with nonimmune thrombocytopenia were included; their mean RI was 0.66 +/- 0.01 SE. Seventeen newborn infants with severe infections were assayed for PAIgG. Eight of nine infants with bacterial infections had increased RI, with a mean of 1.16 +/- 0.03 SE (P less than 0.01). Six of the eight infants with viral infections had elevated RI, with a mean of 1.23 +/- 0.03 SE (P less than 0.01). These findings suggest that an immune mechanism may be involved in the thrombocytopenia of severe neonatal infection.

Drug-induced immune thrombocytopenia

A variety of drugs and other agents have been reported to cause immune-mediated platelet destruction. The cardinal features of this syndrome are acute, often alarming, purpura, closely related to drug exposure, which remits in one to two weeks after discontinuation of all suspect drugs. Quinidine and quinine have been most commonly implicated but, recently, both heparin and heroin have been the subject of numerous reports. Platelets are removed rapidly from the circulation, apparently as a result of the attachment of drug-antibody immune complexes. In vitro documentation of platelet injury by these complexes has inspired the development of many in vitro tests of differing sophistication. While valuable in confirming the clinical suspicion, none is sufficiently sensitive to exclude the diagnosis.

Detection of platelet associated IgG in immune thrombocytopenia: a new assay employing protein A and peroxidase anti-peroxidase (PROA-PAP)

Immune thrombocytopenia is frequently encountered in medical practice and is generally accepted as being caused by an IgG antibody. The capability of detecting platelet-bound IgG as a diagnostic and therapeutic modality is critical for appropriate care and management of patients with idiopathic thrombocytopenic purpura (ITP), as well as other immune thrombocytopenias. We have modified our previous assay (Br J Haematol 37:265, 1977) by employing protein A and PAP as a labeled antibody. Surface bound platelet IgG was quantitated by phase contrast microscopy after incubation with PAP, graded per 100 platelets and expressed as a reactive index (RI). Controls (n=13) had RIs ranging from 0.49 to 0.72 (mean 0.63 +/- 0.02 SE). The nonimmune thrombocytopenic group (n=7) had an RI ranging from 0.58 to 0.72 (mean 0.64 +/- 0.01 SE). In contrast, the immune thrombocytopenic group (n=28) had RIs ranging from 1.04 to 1.75 (mean 1.43 +/- ;0.03 SE). Platelet-associated IgG was evaluated further by absorbing representative sera samples from each group against washed granulocytes, red cells and platelets. Only when sera from the immune thrombocytopenic group were absorbed against platelets did the reactive indices of pre- and postabsorption samples change significantly. These findings suggest that our assay is clinically applicable in detecting platelet-associated IgG in immune thrombocytopenia and has the advantage of being rapid, reproducible and easy to perform in a clinical laboratory.

Post-transfusion purpura: an enigma of alloimmunization

A patient with post-transfusion purpura is reported. This female patient, sensitized by previous blood transfusion, developed symptomatic thrombocytopenia seven days after a second blood transfusion. A platelet antibody, which had anti-P1A1 specificity, was identified by 51Cr-release assay and by indirect immunofluorescence. Hemorrhage stopped abruptly after plasma exchange therapy. Thrombocytopenia did not recur when the patient was further challenged with P1A1-positive blood and plasma. Anti-P1A1 antibody, detectable by immunofluorescence but not by complement-dependent platelet cytoxicity, persisted in high titer for at least one year after recovery. The heterogeneity and pathogenesis of this clinical syndrome are discussed.

A new micromethod for the in vitro detection of antiplatelet antibodies: C-FDA thrombocytotoxicity

A new microtechnique, C-FDA, for the in vitro detection of antiplatelet antibodies, is described. This technique is faster and simpler than either 51Cr thrombocytotoxicity or immunofluorescence (IF). C-FDA is more sensitive than 51Cr for all (anti-HLA, --P1A1, ABO, drug-related, and ITP-related) antibodies tested. Although IF was more sensitive for many types of antibodies, C-FDA was as good or better a clinical test method for all drug-related and isoimmune neonatal thrombocytopenia patient sera tested. Preliminary data also suggest that this method detects possible new non-HLA, non-ABO, nonP1A1 platelet antigens.

Thrombocytopenia in children

Thrombocytopenia in children can be classified on the basis of understanding of the production, life span, and fate of platelets. Thrombocytopenia may be familial, associated with drug-ingestion as a result of immune mediated mechanisms, direct toxicity to circulating platelets, or injury to megakaryocytes, or associated with other disease states.

A microcytotoxicity assay using 111indium oxine release from platelets

A simple, rapid method is described for the labelling of platelets with 111indium oxine for use in a microcytotoxicity assay. The assay described gives low levels of spontaneous lysis, good reproducibility and an end point may be determined by autoradiography as well as by direct measurement of release of 111indium. The labelled platelets, stored at 4 degrees C without further washing, may be used in the assay system for up to 4 days after preparation without loss of reproducibility.

Idiopathic thrombocytopenic purpura occurring in Hodgkin disease after splenectomy: report of two cases and review of the literature

The occurrence of idiopathic thrombocytopenic purpura (ITP) in Hodgkin disease is uncommon. Even more unusual is the development of ITP in Hodgkin disease following splenectomy. This report describes two patients with Hodgkin disease who developed severe ITP with negative platelet antibody studies very soon after splenectomy (20 days in one and three months in the other). A review of the literature of 21 other patients with well-documented ITP and Hodgkin disease indicated that ITP occurring in Hodgkin disease may be more severe and refractory to therapy than ITP unassociated with Hodgkin. Nodular sclerosis or mixed cellularity histologic types of Hodgkin disease were present in all but one of the patients with ITP and Hodgkin disease, and males constituted 65% of cases. There appeared to be no correlation between the onset of ITP and activity of Hodgkin disease. Of five splenectomized patients with Hodgkin disease who developed ITP and were treated with immunosuppressive drugs for thrombocytopenia, three had an excellent response and two had a good response, suggesting that the combination of corticosteroids and immunosuppressive drugs may be indicated at the outset in patients with Hodgkin disease who develop ITP following splenectomy.

Heparin-induced thrombocytopenia: association with a platelet aggregating factor and arterial thromboses

Eleven patients with heparin-induced thrombocytopenia were studied. Thrombocytopenia appeared 3-16 days following the initiation of prophylactic or therapeutic doses of heparin. The mean lowest platelet count recorded was 48,000/mm3. When heparin was stopped, recovery from thrombocytopenia began within 24 hours and was complete by ten days. Two patients developed fatal thromboses, and two others had myocardial infarctions while thrombo-cytopenic. In the serum of seven patients, including three of the four with arterial thrombosis, a heparin-dependent platelet aggregating factor was present. The factor caused release of platelet 14C serotonin but did not lyse platelets. It was present in the globulin fraction of all positive sera, and in one serum studied it was isolated in the IgG/IgA immunoglobulin fraction. The factor was not present in 16 normal sera or in the sera of 15 nonthrombocytopenic patients receiving heparin. Our observations suggest that heparin-induced thrombocytopenia is common and that, in some patients it may be accompanied by severe arterial thrombosis. In vivo platelet aggregation is a possible explanation for the thrombocytopenia and the thrombosis in this disorder.

Deletion of the platelet-specific alloantigen PlA1 from platelets in Glanzmann's thrombasthenia

Expression of a Platelet-specific alloantigen (Pl(A1)) was studied in five unrelated patients with Glanzmann's thrombasthenia using immunologic techniques based on release of (51)Cr from tagged platelets by Pl(A1)-specific antibody. Less than 1% of the normal quantity of Pl(A1) could be detected on platelets of patients 1, 2, and 3; platelets from patients 4 and 5 contained 22 and 12% of normal levels, respectively. After treatment with bromelain, platelets from patients 4 and 5, but not those from patients 1, 2, and 3, released (51)Cr as well as normal Pl(A1)-positive platelets when exposed to anti-Pl(A1). Platelets from each of the five patients reacted normally with drug-dependent antibodies and with autoantibodies specific for platelets. Polyacrylamide gel electrophoresis of thrombasthenic platelets showed marked deficiencies of glycoproteins IIbalpha and III (P < 0.0005), confirming recent reports of others. Deficiency of the two proteins as determined by gel scanning was more pronounced in patients 1, 2, and 3 than in patients 4 and 5. Normal levels of glycoproteins IIbalpha and III were found in platelets from normal subjects negative for Pl(A1). These observations are consistent with the possibility that the Pl(A1) antigen is located on one or both of the glycoproteins lacking in Glanzmann's thrombasthenia, although other explanations are possible. They further suggest that patients with thrombasthenia may be heterogeneous in respect to the degree to which these glycoproteins are deleted. The Pl(A1) antigen can be measured with considerable precision and may provide a marker useful for the diagnosis and study of Glanzmann's disease.