Platelet function defects associated with hemorrhage or thrombosis

Characterization of an In Vitro Platelet Function Analyzer, PFA-100™

A new in vitro system for the evaluation of platelet function, PFA-100 (currently under evaluation) is characterized. The system monitors platelet aggrega tion on a collagen-epinephrine-coated membrane as whole blood sample is aspirated under controlled flow conditions through a microscopic aperture cut into the membrane. The time required for the platelet plug to oc clude the aperture (closure time) is indicative of the plate let function in the sample. Incubation of normal blood samples with antibodies to glycoprotein (GP) Ib, GPIIb- IIIa, von Willebrand factor, or with the peptide Arg-Gly- Asp-Ser, resulted in a concentration-dependent prolonga tion in closure time. An anti-fibrinogen antibody did not impact the closure time. Closure time was also prolonged when the hematocrit or the platelet count was lowered to pathological values. The study indicates that PFA-100 could detect defects in platelet adhesion or aggregation. The simplicity of the test makes PFA-100 unique for rapid screening of a variety of platelet dysfunction.

Immune-mediated hemolytic anemia: understanding the nemesis

IMHA is one of the most common causes of anemia in small animals. Although treatment may be rewarding, many patients do not respond adequately to glucocorticoids alone and require additional immunosuppressive therapy. Some patients may succumb to acute severe anemia and die within the first few weeks of treatment; even if they survive, relapses may occur. IMHA is the nemesis; as our understanding of this disease increases and treatment options expand, it is hoped that survival rates will finally improve.

Discontinuation of the Bleeding Time Test without Detectable Adverse Clinical Impact

Background: The bleeding time (BT) test predicts a higher bleeding complication rate in populations at risk for inherited or acquired platelet dysfunction, but it is of limited assistance in evaluating individual patients. There are no reports of clinical outcomes after discontinuation of the BT test.

Methods: Interviews with a subset of the physicians who had ordered the BT test before discontinuation of the test were conducted. The total number of platelet-aggregation tests, the mean number of monthly, unmodified platelet units transfused, the incidence of kidney biopsy complications, and the number of doses of 1-deamino-8-d-arginine vasopressin (DDAVP) administered 5 months before and after discontinuation of the BT test were compared. We recorded the rates of bleeding complications in the Major Surgery Risk Pool during the 12 months before and the 5 months after the discontinuation of the BT test.

Results: Clinicians reported they did not significantly change their preprocedural work-ups, postpone an invasive procedure, experience an increase in bleeding complications, or increase their use of blood products after discontinuation of the BT test. Platelet-aggregation tests (n = 9, before and after), platelet transfusions (P = 0.958), and DDAVP administration (before = 24; after = 10) did not increase after discontinuation of the BT test. The rate of postprocedural bleeding complications did not increase significantly in either Major Surgery Risk Pool cases (<3ς deviation from the mean rate) or in patients undergoing renal biopsies (P = 0.225 for decrease in hematocrit; P = 1.000 for the percentage of patients transfused) after discontinuation of the BT test.

Conclusions: Our study failed to identify a clinically significant, negative impact of discontinuing the BT test.

Platelet dysfunction as the presenting feature of atypical myelodysplastic syndrome with monosomy 7, normal blood counts and no bleeding tendency

A 71-year-old male patient with atypical myelodysplastic syndrome showing monosomy 7 is described. He presented with severe foot pains, trophic skin and nail changes, loss of distal pulses, all compatible with peripheral arterial occlusive disease. He had completely normal blood counts and no bleeding tendency. Prolonged bleeding time was disclosed by chance, during routine haemostatic studies. An acquired platelet dysfunction was considered, with prolonged bleeding time and large platelets that failed to aggregate in response to arachidonic acid and that had impaired response to collagen and adrenaline. The bone marrow was hypercellular, with numerous dysplastic megakaryocytes and two other slightly dysplastic myeloid lines. Cytogenetic analyses of the bone marrow cells showed a mosaic karyotype: 46,XY/45,XY,-7. On angiography, bilateral thrombosis of the iliac, superficial femoral and popliteal was disclosed. The patient was prepared with platelet transfusions. Arterial thrombectomy and amputation of the left calf were performed. Ten months later, his blood counts showed mild pancytopenia. He died at home. The authors discuss some clinical and pathogenetical aspects of such presentations of myelodysplastic syndromes.

Platelet-associated bleeding disorders

OBJECTIVE

To provide a review of platelet disorders, treatment, and nursing care.

DATA SOURCES

Review articles and book chapters pertaining to quantitative and qualitative platelet disorders.

CONCLUSIONS

Platelet-associated bleeding disorders are classified as quantitative (abnormal number), qualitative (abnormal function), or hypercoagulable states (errors in hemostasis). The resulting complications include thrombocytosis, thrombocytopenia, hypercoagulation, or bleeding dyscrasias. The administration of drugs, plasma, or platelet therapy may be beneficial to these patients.

IMPLICATIONS FOR NURSING PRACTICE

Patients with platelet disorders are at great risk of life-threatening hemorrhage and require close monitoring to prevent unnecessary sequelae. Patient instruction to prevent trauma is required.