Quantitative and qualitative platelet disorders

Platelet disorders are common during childhood. Those conditions that are clinically significant are generally diagnosed with ease. Qualitative platelet disorders rarely cause clinical problems. The armamentarium of diagnostic tests, although limited, is usually satisfactory to allow for accurate diagnosis and effective treatment of those children with platelet disorders who are at risk of hemorrhage.

Platelet transfusion

The statement printed below was agreed at a consensus conference on platelet transfusion organised by the Royal College of Physicians of Edinburgh and held in Edinburgh in November 1997. We publish this statement at the request of the organising committee to bring it to the attention of physicians who do not read the haematological literature. The statement will also appear in the British Journal of Haematology in 1998 with the scientific evidence upon which it is based.

Platelet disorders in newborn infants: diagnosis and management

Platelets are small, disc-shaped, anucleated cells formed by fragmentation of megakaryocytes in the bone marrow. They circulate in blood with a lifespan of 7 to 10 days and, together with fibrin, form hemostatic plugs at sites of vessel injury. Abnormalities of platelets, either quantitative or qualitative, may cause clinically significant bleeding with resultant morbidity and, on occasion, mortality. This review will focus on platelet disorders in neonates, defined as infants of up to 4 months of age. Special emphasis will be given to the physiology of platelet function in healthy and sick newborn infants. The review will be divided into sections as follows: role of platelets in hemostasis, platelet function in newborn infants, quantitative platelet disorders, qualitative platelet disorders, and platelet transfusion therapy.

[The therapeutic correction of disorders in thrombocyte-vascular hemostasis and of changes in the rheological properties of the blood in patients with arterial hypertension]

158 patients with essential hypertension received beta-adrenoblockers and were exposed to travelling impulse magnetic field, magnetolaser radiation. The study of platelet-vessel hemostasis and blood rheology revealed a relation of good clinical response and increased exercise tolerance with initial platelet dysfunction and rheological disorders which underwent positive changes in the course of treatment.

Use of blood and blood components in canine and feline patients with hemostatic disorders

Therapy with blood and blood products related to hemostatic disorders in small animal practice is reviewed. Administration of platelet rich plasma and platelet concentrates in thrombocytopenia or thrombopathia is discussed. Vascular purpuras, vasculitis, and vascular inherited defects are also considered. Inherited coagulation disorders are summarized and the therapeutic choices in treating these disorders are also proposed. In addition, acquired coagulation disorders are briefly reviewed.

Disorders of platelets in pregnancy

No significant change in platelet number, function or life-span occurs during pregnancy. However, pregnancy may be complicated by various platelet abnormalities or platelets may be involved in pregnancy pathologies. Thrombocytopenia is the most common platelet disorder to affect pregnancy. It may occur in a number of clinical conditions and both immune and nonimmune mechanisms may be involved. Apart from the risks to the mother, the fetus may be secondarily affected, especially in cases of immunogenic thrombocytopenia. Management of the mother may not necessarily improve fetal prognosis. Improvement in diagnostic techniques like percutaneous umbilical blood sampling (PUBS) has greatly improved in utero diagnosis and management of the affected fetus. The diagnosis and management of the various platelet disorders affecting the pregnant woman and the fetus are discussed in this overview.

Hematologic aspects of end-stage renal failure

Renal dysfunction may give rise to a variety of hematologic disturbances, including anemia, leukocyte dysfunction, and coagulopathy. The anemia of renal failure has been attributed to a relative deficiency of erythropoietin, but absolute deficiencies of iron or folate may also play a role. Other contributing factors include heavy-metal toxicity, blood loss, and a reduction in red cell survival induced by toxic radicals. The treatment of the anemia of renal disease has advanced with the development of recombinant human erythropoietin. At subcutaneous doses of 50-75 IU/kg triweekly in selected patients, normalization of hemoglobin is presently possible. The coagulopathy of renal disease consists of an acquired qualitative platelet defect, best remedied by dialysis but also treated successfully by rHuEPO, cryoprecipitate or DDAVP, and conjugated estrogens. Uremia-induced leukocyte dysfunctions include diminished granulocyte chemotaxis, phagocytosis, and bactericidal activity. Cell-mediated immune defects and hypogammaglobulinemia have also been described. The pathophysiology of the hematologic manifestations of uremia is discussed. Therapeutic recommendations for dealing with anemia, bleeding, and infectious complications of renal failure are described.

Hemostasis in renal disease: pathophysiology and management

The hemostatic abnormalities commonly encountered in patients with renal disease can significantly threaten the well-being of the patient and pose difficult management issues for the clinician. In this review, we explore the pathophysiology underlying the bleeding diathesis and hypercoagulability that can occur. Current therapeutic interventions are also discussed.

Coagulation activation in diabetes mellitus: the role of hyperglycaemia and therapeutic prospects

Numerous studies have shown that coagulation abnormalities occur in the course of diabetes mellitus, resulting in a state of thrombophilia. These observations are supported by epidemiological studies which demonstrate that thromboembolic events are more likely to occur in diabetic patients. The coagulation abnormalities observed in diabetic patients seem to be caused by the hyperglycaemia, which also constitutes the distinguishing feature of this disease. These data are also supported by in vitro studies which demonstrate how glucose can directly determine alterations in the coagulation system. The abnormalities observed involve all stages of coagulation, affecting both thrombus formation and its inhibition, fibrinolysis, platelet and endothelial function. The final result is an imbalance between thrombus formation and dissolution, favouring the former. Hyperglycaemia probably determines the onset of these abnormalities through three mechanisms which are, respectively, non-enzymatic glycation, the development of increased oxidative stress and a decrease in the levels of heparan sulphate. The first seems to affect the functionality of key molecules of coagulation in a negative sense. Oxidative stress constitutes an important pro-thrombotic stimulus, while the decrease in heparan sulphate determines a reduction in antithrombotic defenses. Good metabolic control could play a key role in controlling the coagulation irregularities in diabetes. However, considering the difficulties in achieving such an objective, it is possible that the use of drugs may represent a valid alternative. In fact, several drugs exist which are of potential interest. It is, however, necessary to perform long-term studies which demonstrate unequivocably that by controlling the coagulation abnormalities in diabetic patients, prolongation of life is possible.

Common blood disorders: a primary care approach

Many anemias and diseases of the blood-forming elements increase in incidence with advancing age. Iron deficiency remains the cause of most cases of anemia and may be related to inapparent blood loss. Other responsive anemias that can be managed by the primary care physician include vitamin B12 and folate deficiencies and drug- or autoimmune-related hemolytic anemia. Nonresponsive anemias, including hematologic malignancies, are quite common in older patients and require referral to a specialist. Platelet disorders are often produced by certain drugs and, like most refractory anemias, often require a bone marrow aspirate for diagnosis.

A liposome based platelet substitute, the plateletsome, with hemostatic efficacy

The complexity of platelet mediated hemostasis has hindered development of a platelet substitute for transfusion therapy. In the current study, the hemostatic efficacy of a liposome based modality, the plateletsome, is demonstrated. A deoxycholate extract of a platelet membrane fraction, with a minimum of 15 proteins including GPIb, GPIIb-IIIa and GPIV/III, was incorporated into sphingomyelin: phosphatidylcholine: monosialylganglioside or egg phosphatide small unilamellar vesicles by reverse-phase/sonication and French press extrusion. These plateletsomes decreased bleeding by 67% in the tail bleeding time in rats made thrombocytopenic (platelets < 30,000/microliters) with external irradiation (7-9Gy) by Cesium source. Efficacy was also demonstrated in the thrombocytopathic, Fawn-Hooded rat, but to a lesser extent than in the thrombocytopenic animals. Direct plateletsome infusion to the tail wound was more effective than systemic administration for all effective preparations. On post-mortem examination, no pathologic thrombi were detected by gross and histopathologic examination of the lungs, livers, kidneys, or spleens of thrombocytopenic or normal animals after plateletsome infusion. No evidence of intravascular coagulation, monitored by levels of circulating fibrinogen and platelet counts, was observed when plateletsomes were administered intravenously to rabbits. No deleterious effect, either inhibition or hyperaggregability, on platelet aggregation studies in vitro was observed. While further refinements are clearly required, this study indicates that liposomes bearing specific platelet proteins may provide a basis for a clinically applicable platelet substitute.

Disorders of platelet function

Platelets provide for primary hemostasis by forming a hemostatic plug at sites of vascular damage. They also provide a surface for the assembly of the coagulation protein complexes that generate thrombin, serve as a nidus for fibrin clots, and secrete factors involved in wound repair. Normal platelet function can be divided into four phases: adhesion, aggregation, secretion, and expression of procoagulant activity. Platelet adhesion initiates plug formation as platelets adhere to the connective tissue at the edges of a wound within seconds after vascular damage. When damage occurs in regions of slow blood flow, platelets adhere to subendothelial collagen, fibronectin, and laminin. However, when damage occurs in regions of rapid flow, platelet adhesion requires the presence of subendothelial von Willebrand factor (vWf) and a specific platelet receptor, the glycoprotein Ib/IX (GPIb/IX) complex. Following initial adhesion, platelets aggregate to complete the formation of a hemostatic plug. Platelet aggregation requires active platelet metabolism, platelet stimulation by agonists such as ADP, thrombin, collagen, or epinephrine; the presence of calcium or magnesium ions and specific plasma proteins such as fibrinogen or vWf; and a platelet receptor, the glycoprotein IIb/IIIa (GPIIb/IIIa) complex. Thus, platelet stimulation results in the generation of intracellular second messengers that transmit the stimulus back to the platelet surface, exposing protein binding sites on GPIIb/IIIa. Fibrinogen (or vWf) then binds to GPIIb/IIIa and crosslinks adjacent platelets to produce platelet aggregates. Platelet stimulation also results in platelet secretion and the elaboration of platelet procoagulant activity. During secretion, substances are released to propagate the aggregation response and to promote wound healing; the expression of procoagulant activity localizes thrombin generation to the site of vascular damage. Disorders of platelet function can be divided into those of congenital and those of acquired origin. Although congenital disorders are uncommon, acquired disorders are encountered frequently in clinical practice. Congenital absence of GPIb/IX and GPIIb/IIIa results in the Bernard-Soulier syndrome (BSS) and Glanzmann thrombasthenia (GT), respectively. Each is an autosomal recessive bleeding disorder in which absence of a protein complex renders the affected platelets incapable of undergoing either vWf-mediated adhesion (BSS) or fibrinogen-mediated aggregation (GT).(ABSTRACT TRUNCATED AT 400 WORDS)

Disorders of platelet function: evaluation and treatment

Platelet function involves adhesion, aggregation, secretion, and elaboration of procoagulant activity. Compromise of any of these functions due to an inherited or acquired defect in primary hemostasis can result in bleeding diatheses. Acquired disorders are related to drugs, systemic disease, or hematologic disease. Although laboratory tests are available to evaluate platelet function, the history is of prime importance in the diagnostic workup. Plasmapheresis, dialysis, transfusion of normal platelets, administration of cryoprecipitate, and administration of corticosteroids are all acceptable treatment protocols in specific situations. The drug of choice for treating mild hemostatic abnormalities due to platelet function defects is desmopressin acetate, which may be administered by several routes, produces few, if any, side effects, and carries no risk of infectious disease transmission.

Intravenous gamma globulin decreases platelet-associated IgG and improves transfusion responses in platelet refractory states

In an attempt to improve platelet transfusion responses, intravenous immunoglobulin (IV-IgG) was administered to 19 patients who were refractory to random and best available HLA-matched platelets. A response to IV-IgG was defined as two or more successive transfusions of HLA-matched products that provided recoveries greater than 30%. Thirteen of 19 (68%) patients responded to therapy at a median time of 7 days after initiation of IV-IgG (range = 2-17). Baseline platelet associated IgG levels (PalgG) were elevated in both the responders (61.6 +/- 76.2) (mean +/- SD) and the non-responders (47.0 +/- 46.3 fg/plt). Post-therapy, PalgG levels remained unchanged in the nonresponders but were decreased significantly (p = 0.05) to 11.1 +/- 6.2 fg/plt in the responders. The latter levels were similar to those (11.6 +/- 8.2 fg/plt) measured in a series of 36 transfusion responsive patients. This apparent decline in PalgG was not explained by differences in lymphocytotoxic antibodies (LCT-Ab) after therapy. Moreover, a high degree of alloimmunization was associated with a poorer response to IgG. Only two of eight patients with LCT panel-reactive antibody (PRA) of greater than 85% were responders. By contrast, improved transfusion outcomes were seen uniformly in patients with PRA greater than or equal to 85%. Improved recoveries were obtained using LCT-Ab compatible but not incompatible platelets. The median increment (% predicted) with compatible platelets before therapy was 6.0 +/- 9.9 (SD). Post-IgG, median recoveries were 37.0 +/- 31.2 percent, P less than 0.001. These findings suggest that IV-IgG may alter destructive mechanisms that affect the survival of compatible platelets in refractory patients.

[Plasma exchange in a case of HELLP syndrome associated with disseminated intravascular coagulation]

The Authors describe a case of HELLP syndrome associated with disseminated intravascular coagulation occurred after delivery in a patient with late hypertension without any sign or symptom of preeclampsia during pregnancy. The use of plasma exchange has contributed to the recovery from the pathology.

Acquired platelet dysfunction in patients with uremia

The current status of knowledge of the uremic hemorrhagic diathesis is reviewed. Discussions of clinical features, classification and pathogenesis, retention products and hemostatic defects, and therapy are included.

Congenital disorders of platelet function

Platelets play a major role in normal hemostasis and congenital defects in platelet function are associated with bleeding manifestations that are largely mucocutaneous in origin and markedly variable in severity. They arise by different mechanisms and may be classified as disorders of: (1) platelet-agonist interaction, (2) platelet-vessel wall interaction (vWD and Bernard-Soulier syndrome), (3) platelet-platelet interaction (congenital afibrinogenemia and Glanzmann's thrombasthenia), (4) platelet secretion, and (5) platelet-coagulant protein interaction. Excluding vWD, most congenital platelet dysfunctions currently fall in the category of platelet secretion defects. Some of these patients have storage pool deficiency or defects in thromboxane synthesis, but the majority have normal granule stores. The underlying mechanisms in this large, heterogeneous group of dysfunctions remain to be elucidated. Bleeding episodes of vWD are managed by the administration of DDAVP or cryoprecipitate. The major treatment modality in the management of bleeding episodes and surgical procedures in patients with congenital platelet defects is platelet transfusions. Evidence is becoming available that many of these patients may respond to intravenous infusion of DDAVP with a shortening of the bleeding time. The specific groups of patients who will respond, and the efficacy of DDAVP in clinical situations remains to be established.

Transfusion of infants with activation of erythrocyte T antigen

A protocol for transfusion of infants with erythrocyte T-antigen activation was evaluated for safety and effectiveness in a prospective, 3-year, sequential series of 1672 infants admitted for intensive care. Erythrocyte T antigens are activated by enzymes produced by clostridia or other bacteria in infants with sepsis, often in association with necrotizing enterocolitis. Transfusion of these infants with blood products containing plasma carries the risk of causing intravascular hemolysis. Our transfusion protocol included testing for T-antigen activation, restricting transfusion of patients with activated T antigens to washed erythrocytes or washed platelets whenever possible, and selecting donors with low-titer anti-T when plasma-containing blood products were required. In this series, 10 patients had T-antigen activation, including four with clostridial infections. Severe hemolysis occurred in one patient who received plasma before T-antigen activation developed. Of five patients who received low-titer anti-T plasma, mild hemolysis occurred in three and no hemolysis in two. Four patients who received no plasma-containing blood products experienced no hemolysis. Used cautiously, this protocol allows a full range of transfusion therapy to infants with T-antigen activation.

Bernard-Soulier syndrome complicating pregnancy: a case report

The pregnancy of a patient with Bernard-Soulier syndrome is described. Coagulation abnormalities were encountered, as well as isoimmunization from previous transfusions. Immune suppression was achieved with steroids and intravenous gamma globulin, and plasmapheresis was performed to allow platelet transfusion.

Quantitative platelet disorders

Thrombocytopenia may be caused by abnormal platelet production, accelerated removal owing to immunologic or nonimmunologic reasons, or sequestration of platelets in the spleen. Bleeding associated with thrombocytopenia usually presents as petechial or ecchymotic hemorrhages or epistaxis. Immunologic and nonimmunologic cases of thrombocytopenia may be diagnosed with routine hematology, bone marrow cytology, and platelet specific tests. Thrombocythemia may also be associated with platelet functional abnormalities, contrasting the normal platelet function noted in reactive thrombocytosis.

Bleeding and coagulation disorders in the elderly

Ageing does not bring with it any major changes in the coagulation or fibrinolytic proteins or platelets. It does bring a greater burden of disease, with less reserves, and so when haemorrhage occurs in the elderly it has more serious consequences. The cause of a bleeding diathesis can usually be determined after a careful history, and examination of the patient followed by simple tests--the platelet count, blood film, bleeding time, prothrombin time, partial thromboplastin time, thrombin time, fibrin degradation products and the euglobulin clot lysis time. Other confirmatory tests, assays and inhibitor titres, will seal the diagnosis. Treatment is mainly directed at removing the underlying cause, if possible, and remedying the defect, with platelet transfusion, fresh frozen plasma or factor concentrates. These treatments will not be effective where there is an inhibitor or antibody present; steroids, splenectomy (for ITP), plasma exchange or immunosuppression are needed. Two major advances have occurred in the early 1980s. One has been the introduction of high-dose intravenous immunoglobulin in the management of ITP, although worries remain about thrombotic events in elderly patients. The other is the spreading use of DDAVP, originally introduced for von Willebrand's disease and mild haemophilia, and now finding a role in uraemia and with cardiopulmonary bypass. Drugs are a significant and potentially preventable cause of bleeding in the elderly. The most frequent problems arise with anticoagulants. The risk of interactions increase with the number of other medications which are prescribed.

[Blood coagulation disorders]

Disorders of hemostasis are frequently encountered, and, if not recognised as early as possible, in particular prior to surgery, may lead to bleeding complications which are much more difficult to treat than those where exact diagnosis permits specific preventive therapy. A first case report on a woman with an acquired inhibitor against factor VIII illustrates that even minor injury may lead to hemorrhage necessitating blood transfusion. Furthermore, as long as the defect remains inaccessible to successful substitution therapy, wound healing will not take place. A second case report describes a patient with a congenital dysfunction of blood platelets, and serves as an example for similar disorders which, if unrecognised, lead to multiple, otherwise avoidable complications. Unfortunately there is no clearcut correlation between a given defect of hemostasis and bleeding manifestations, since psychological factors, among others, appear to influence the occurrence of "spontaneous" hemorrhage. Any unexpected and unexplained bleeding complication requires careful evaluation of the possible underlying causes, since such investigations often not only affect the future of the propositus himself but also that of his family members.

Treatment of severe platelet dysfunction and hemorrhage after cardiopulmonary bypass: reduction in blood product usage with desmopressin

Impairment of platelet function commonly occurs after cardiopulmonary bypass, and may result in substantial bleeding. Because desmopressin acetate (a synthetic analogue of vasopressin) shortens bleeding time in a variety of platelet disorders, a controlled clinical trial of intravenous desmopressin was performed in 39 patients with excessive mediastinal bleeding (greater than 100 ml/h) and a prolonged template bleeding time (greater than 10 minutes) more than 2 hours after termination of cardiopulmonary bypass. Twenty-three desmopressin recipients and 16 control patients (no desmopressin) were similar in surgical procedure, pump time, platelet count, template bleeding time and amount of bleeding before therapy (p = NS). Compared with the control group, the patients receiving desmopressin (20 micrograms; mean 0.3 micrograms/kg) utilized fewer blood products (29 +/- 19 versus 15 +/- 13 units/patient; p less than 0.05), especially platelets (12 +/- 9 versus 4 +/- 7 units/patient; p = 0.004), while achieving a similarly effective reduction in mediastinal bleeding (4.8- and 4.3-fold, p = 0.001 for both). Severe platelet dysfunction was partially corrected within 1 hour after desmopressin infusion, during which interval no blood products were administered: the template bleeding time shortened (from 17 to 12.5 minutes, p less than 0.05), whereas the platelet count remained unchanged (at 96 +/- 35 and 105 +/- 31 X 10(3)/mm3, p = NS). The plasma levels of two factor VIII components increased: procoagulant activity (VIII:C) from 0.97 +/- 0.43 to 1.52 +/- 0.74 units/ml (p less than 0.05) and von Willebrand factor (VIII:vWF) from 1.28 to 1.78 units/ml (p less than 0.05); these increases correlated with the shortening of the bleeding time (p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Hematologic emergencies

Hematologic emergencies require thorough but prompt evaluation of the patient, availability of relatively routine laboratory tests, and immediate decisions. This article discusses the emergencies associated with red blood cell disorders, white blood cell disorders, hemostatic disorders, and transfusion reactions.

Progenitor cell defect correctable by bone marrow transplantation in five independent mouse models of platelet storage pool deficiency

Two human platelet storage pool deficiencies (SPD), Hermansky-Pudlak syndrome and Chediak-Higashi syndrome, are recessively inherited and characterized by hypopigmentation, prolonged bleeding, and normal platelet numbers accompanied by a reduction of platelet dense granules. Seven independent and unique mouse pigment mutations regulated by separate genes have been proposed as animal models for SPD. Mice homozygous for the recessive mutations have diluted pigmentation, prolonged bleeding times, normal platelet concentrations, and reduced numbers of platelet dense granules. Reciprocal bone marrow transplantations were carried out between normal C57Bl/6J mice and five of these mutants, pearl, light ear, pale ear, ruby-eye, and maroon, to test whether the platelet defects are due to platelet progenitor cells or to humoral regulatory factors. Recipient mice were transplanted with marrow after 950-rad whole body irradiation. The prolonged bleeding time and low serotonin concentrations of the five mutants were converted to normal values after transplantation with normal marrow. Normal mice displayed characteristics of platelet SPD when transplanted with mutant marrow. This study demonstrates that in each of five independent mouse models the thrombopathy of SPD is due to a platelet progenitor cell defect correctable by bone marrow transplantation. These findings suggest that in severe cases human SPD may be amenable to treatment by bone marrow transplantation.

Correction of symptoms of platelet storage pool deficiency in animal models for Chediak-Higashi syndrome and Hermansky-Pudlak syndrome

Two human diseases of platelet storage pool deficiency (SPD), Hermansky-Pudlak syndrome and Chediak-Higashi syndrome, are recessively inherited disorders characterized by hypopigmentation, prolonged bleeding, and normal platelet counts accompanied by a reduction in dense granule number. We have recently described seven independent recessive mutations in the mouse regulated by separate genes which are likely animal models for human SPD. Reciprocal bone marrow transplants were carried out between normal C57BL/6J mice and two of these mutants, beige and pallid, in order to test whether the platelet defects are due to a defect in platelet progenitor cells or to humoral factors. Normal and congenic mutant mice were transplanted with marrow after 950 rad whole body radiation. The long bleeding times and low serotonin concentrations of the two mutants were converted to normal values after transplantation with normal marrow. Likewise, normal mice displayed symptoms of SPD when transplanted with mutant marrow. These studies demonstrate that with each of the two mutations, platelet SPD results from a defect in bone marrow precursor cells. Also, the studies suggest that in severe cases, platelet SPD may be successfully treated by bone marrow transplantation.

Newborn haemostasis

Although reliable haemostasis testing is difficult to obtain in the newborn infant, information gained from such testing is important to the diagnosis of hereditary and acquired haemostatic disorders. Newborn infants are at risk for developing haemorrhage or thrombosis when provoked by various pathological stimuli. Haemostasis screening tests and factor assays must be interpreted using gestational age-specific normal ranges. Frequently, the comparison of several factor assays provides the necessary information to diagnose and treat neonatal haemostatic abnormalities.