Platelet Function Disorders
Platelet function disorders are hemorrhagic disorders that resemble thrombocytopenia but stem from platelet dysfunction rather than platelet deficiency. They characteristically cause defects in platelet adhesion or procoagulation activity (ability to bind coagulation factors to their surface to form a stable fibrin clot). Such disorders may also create defects in platelet aggregation and thromboxane A2 and may produce abnormalities by preventing the release of adenosine diphosphate (defective platelet release reaction). The prognosis varies widely.
Causes
Platelet function disorders may be inherited (autosomal recessive) or acquired. Inherited disorders cause the bone marrow to produce platelets that are ineffective in the clotting mechanism. Acquired disorders result from the effects of drugs, such as aspirin and carbenicillin; from systemic diseases such as uremia; and from other hematologic disorders.
Complications
Hemorrhage is the most serious complication of platelet function disorders.
Assessment
The patient history discloses the sudden occurrence of excessive bruising and nasal and gingival bleeding. It may also reveal the use of drugs (especially aspirin) that might be the cause of the problem or a family history of bleeding disorders that cause platelet dysfunction.
Skin inspection reveals petechiae and purpura. External hemorrhage may also be present. The patient’s vital signs are usually normal. However, with hemorrhage, the patient’s pulse and respiratory rates will rise and his blood pressure will decrease.
Another serious sign—internal hemorrhage into the muscles and visceral organs—may not be immediately obvious. Occasionally, this disorder is first identified by excessive bleeding during surgery.
Diagnostic tests
Prolonged bleeding time in a patient with a normal platelet count and normal clotting factors suggests this diagnosis. Determination of the defective mechanism requires a blood film and a platelet function test to measure platelet release reaction and aggregation. Depending on the type of platelet dysfunction, some or all test results may be abnormal.
Other typical laboratory findings include poor clot retraction; decreased prothrombin conversion; and normal prothrombin, activated partial thromboplastin, and thrombin times. Baseline testing includes a complete blood count and differential and appropriate tests to determine hemorrhage sites.
Treatment
Platelet replacement is the only satisfactory treatment for inherited platelet dysfunction. However, platelets may need to be human leukocyte antigen (HLA)-matched to ensure that the body doesn’t reject them.
Acquired platelet function disorders respond to adequate treatment of the underlying disease or discontinuation of damaging drug therapy.
Plasmapheresis effectively controls bleeding caused by a plasma element that’s inhibiting platelet function. During this procedure, one or more units of whole blood are removed from the patient, the plasma is removed from the whole blood, and the remaining packed
red blood cells are reinfused. (See Understanding plasmapheresis.)
red blood cells are reinfused. (See Understanding plasmapheresis.)
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