One of the best indicators of platelet deficiency is prolonged bleeding after a controlled superficial injury; that is, capillaries subjected to a small, clean incision bleed until the defect is plugged by aggregating platelets. When platelets are inadequate in number or if their function is impaired, bleeding time is prolonged.
If the platelet count falls below 10,000/mm3, bleeding time is prolonged. Prolonged bleeding time with a platelet count of greater than 100,000/mm3 indicates platelet dysfunction. Bleeding time is prolonged in von Willebrand's disease, an inherited deficiency of vWF, a protein associated with clotting factor VIII that is necessary for normal platelet adherence. Aspirin ingestion also prevents platelet aggregation and may prolong bleeding time for as long as 5 days after a single 300-mg dose.24 Other causes of prolonged bleeding times are listed in Table 2-4.
Values vary according to the method used to perform the test (see the section on procedure).
When the platelet count is low, bleeding time may be calculated from platelet numbers using the following formula. The result should be evaluated in relation to the normal values for the Ivy and template methods.
The calculated value also may be compared with the actual results of bleeding time obtained by the Ivy and template methods. An actual bleeding time longer than the calculated result suggests defective platelet function in addition to reduced numbers. It is also possible to detect above-normal hemostatic capacity in cases in which active young platelets compose the entire population of circulating platelets, because young platelets have enhanced hemostatic capabilities.25 This phenomenon may be seen in disorders involving increased platelet destruction (see Table 2-3).
Nursing Care Before the Procedure
Explain to the client:
Aspirin and aspirin-containing medications should be withheld for at least 5 days before the test. Other drugs that may prolong bleeding time (see Table 2-4) should also be withheld.
The test may be performed using the Duke, Ivy, or template method. All three methods involve piercing the skin and observing the duration of bleeding time from the puncture site. Welling blood must be removed, but gently so as not to disrupt the fragile platelet plug. After the skin is pierced, oozing blood is removed at 15-second intervals by touching filter paper to the drop of blood without touching the wound itself. As platelets accumulate, bleeding slows and the oozing drop of blood gets smaller. The end point occurs when there is no fluid blood left to produce a spot on the filter paper.26 The test is timed with a stopwatch.
For all methods, the site to be used is cleansed with antiseptic and allowed to dry. In the Duke method, the earlobe is incised 3 mm deep with a sterile lancet. For the Ivy and template methods, the volar surface of the forearm is used. A blood pressure cuff is applied above the elbow and inflated to 40 mm Hg; the pressure is maintained throughout the test. In the Ivy method, two incisions 3 mm deep are made freehand with sterile lancets. In the template method, two incisions, each 1 mm deep and 9 mm long, are made with a standardized template. The advantage of the template method is the fact that it provides the ability to achieve a reproducible, precise incision every time.
The elapsed time at the point when bleeding ceases is recorded. If bleeding persists beyond 10 minutes, the test is discontinued and a pressure dressing is applied to the puncture site(s).
Nursing Care After the Procedure
When the test is completed, a sterile dressing or Band-Aid is applied to the site. For persistent bleeding, ice may be applied to the site in addition to the pressure dressing.