Acquired Qualitative Platelet Disorders

Platelet function defects associated with hemorrhage or thrombosis

Platelet dysfunction, especially acquired forms, is a common cause of hemorrhage, especially when associated with trauma or surgery. Although the hereditary platelet function defects are generally quite rare, hereditary storage pool disease is common enough to be suspected in an individual, usually a child, with characteristic historical and clinical findings. The acquired platelet function defects, especially those resulting from drugs, are common and should promptly be suspected in patients developing easy and spontaneous bruising, mild-to-moderate mucosal membrane hemorrhage, or unexplained bleeding associated with trauma or surgery. The template bleeding time is generally useful as a screening test of platelet function, but a normal template bleeding time, in the face of a suggestive history, suggestive clinical findings, or in a patient frankly bleeding, is not reliable, and platelet aggregation or lumiaggregation should be done in appropriate clinical situations. Also, prolongation of the template bleeding time is an unreliable predictor of clinical bleeding propensity. The mainstay of therapy for almost all these defects, if bleeding is significant, is the liberal infusion of appropriate numbers of platelet concentrates. The acquired platelet function defects should also be managed by attempts to treat or control the underlying disease, if possible, and offending drugs or potentially offending drugs should immediately be stopped.

Evidence for a storage pool defect in platelets from cirrhotic patients with defective aggregation

The mechanisms underlying the defective platelet function in cirrhotic patients were investigated. Eleven cirrhotic patients with mild disease (group 1), 20 patients with severe cirrhosis (group 2), and 31 controls were studied. Platelet aggregation was significantly reduced in cirrhotics compared with controls. Compared with controls, cirrhotic patients in group 2 showed a significant reduction in the total content of adenosine triphosphate (57.8 +/- 7.8 vs. 26.1 +/- 6.3 mumol/10(11) platelets; P less than 0.05), 5-hydroxytryptamine (285 +/- 26 vs. 104 +/- 38 nmol/10(11) platelets; P less than 0.05), beta-thromboglobulin (2129 +/- 120 vs. 1223 +/- 161 ng/10(8) platelets; P less than 0.01), and platelet factor 4 (1389 +/- 108 vs. 805 +/- 176 ng/10(8) platelets; P less than 0.05). In patients with severe disease, an increase in plasma beta-thromboglobulin-platelet factor 4 ratio, an index of in vivo platelet activation, was observed (controls, 3.50 +/- 0.50; group 1, 4.02 +/- 0.80; and group 2, 6.59 +/- 1.15). Our data indicate the existence of a platelet storage pool defect, which may favor the bleeding tendency of cirrhotic patients.

Hemostatic complications in young patients with essential thrombocythemia

PURPOSE

The purpose of this study was to determine the incidence of hemostastic complications in young patients with essential thrombocythemia (ET).

PATIENTS AND METHODS

The clinical course of 44 patients under the age of 45 with the diagnosis of ET was reviewed in a retrospective manner. Patients were collected from three medical centers in the United States and Italy: the Brigham and Women's Hospital and the Harvard Community Health Plan, Boston, Massachusetts, and the Ospedali Riuniti di Bergamo, Bergamo, Italy.

RESULTS

The overall incidence of hemorrhage or thrombosis, or both, in this group of patients was 39% (17 of 44), with serious complications occurring in 23% (10 of 44). Two patients died of thrombotic events. Neither the presence of symptoms at diagnosis nor any single laboratory parameter proved predictive of clinical sequelae. Treatment with antiplatelet drugs or platelet-lowering agents was not protective.

CONCLUSION

We conclude that ET in young patients may result in serious and life-threatening hemostatic problems and consequently that young age is not a favorable prognostic factor in this disease.

Evaluation of the clinical utility of platelet aggregation studies

To determine the diagnostic importance of platelet aggregation studies, we evaluated the clinical utility of these assays by a retrospective review of 188 adult patients initially studied for bleeding abnormalities with platelet aggregation tests at a tertiary care hospital from 1984 to 1987. The primary indications for requesting the tests in our patient population were for the evaluation of a positive bleeding history or abnormal bleeding time (68%), hypercoagulability (17%), thrombocytosis (9%), or a family history of a bleeding disorder (6%). There was a statistically higher incidence of platelet aggregation test abnormalities in patients with highly abnormal bleeding times (40%), in patients with thrombocytosis from myeloproliferative disorders (65%), and in patients with a family history of a bleeding disorder (58%), compared to the other groups studied (16-29%). Of the 64 platelet aggregation tests performed that were abnormal, the following abnormalities were identified: 19 aspirin-like defects (poor response to arachidonate and decreased second wave responses to weak agonists), which were presumably drug-induced, ten myeloproliferative-type disorder defects (abnormal response to epinephrine predominantly) in patients known to have myeloproliferative disease, 34 abnormal patterns not characterized as aspirin or myeloproliferative disorder related, four of which ultimately led to a diagnosis of storage pool disease, and one spontaneous aggregation defect. Our results suggest that platelet aggregation tests rarely lead to the diagnosis of a specific, previously undiagnosed platelet function disorder. Specific recommendations are given for efficient utilization of platelet aggregation tests.

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.

Hematologic problems in the preoperative patient

A number of topics have been reviewed pertaining to hematologic problems in preoperative patients. Most if not all of the problems discussed can be evaluated reasonably well by history, physical examination, and a few simple laboratory tests. Because the morbidity arising from some of these abnormalities can be quite significant, evaluation and treatment should be completed prior to surgery whenever possible. It is also critical to recall that therapy for a number of hematologic problems involves the transfusion of blood or blood products. This therapy should not be taken lightly as both immediate reactions (fever, anaphalaxis, hemolysis) as well as delayed effects (allosensitization and viral infections) occur frequently. The prudent clinician should try to minimize his patients' exposure to these potentially toxic materials by using alternative therapies.

Laboratory investigation of platelet function: a review of methodology

Over the past decade interest in and knowledge about the role of platelets in the haemostatic process and in various pathological conditions has continued to grow. The scope of laboratory methodology to investigate platelet function in clinical haemorrhagic and thrombotic disorders in the specialised haemostasis unit has also proportionally widened. After highlighting the physiological processes of the role of platelets in the haemostatic mechanism this brief review comments critically on the available routine techniques used to study platelet function in patients who present primarily with a bleeding tendency.

The myelodysplastic syndromes--a study of haemostatic function and platelet ultrastructure

The myelodysplastic syndromes (MDS) are characterised by dysplastic marrow and cytopenia. Clinically detectable bleeding is uncommon and usually attributed to thrombocytopenia. We have investigated some aspects of haemostatic function in 17 patients with MDS and compared the results with findings from 17 control patients matched for age and sex. No specific disorder of blood coagulation or fibrinolysis was identified. The main abnormalities observed in the patients were: prolongation of the bleeding time which was greater than could be explained on the basis of thrombocytopenia in 13 patients; absent, or severely impaired platelet aggregation in response to collagen in 7 patients; impaired platelet production of malondialydehyde when stimulated with collagen and abnormal release of 14C-5 hydroxytryptamine in 5 patients; and abnormalities of ultrastructure in all 5 patients whose platelets were viewed by electron microscopy.