Điều này cần được dưới ngưỡng tác động để cho phép một biên độ an toàn trong bất kỳ bệnh nhân và để đảm bảo rằng sẽ có một kết quả thỏa đáng (cải thiện các triệu chứng) từ truyền máu. Mục tiêu truyền, tuy nhiên, không cần phải nằm trong phạm vi bình thường. Mức độ bất thường mà một bệnh nhân có thể duy trì một khi kết quả xét nghiệm bắt đầu chuyển từ phạm vi bình thườn. | Clinical Decisions and Response Monitoring 109 Fig. . Clinical transfusion decision-making. Theoretical relationship between the severity of clinical symptoms and the degree of abnormality of a laboratory test result. 26 posttransfusion result. This should be below the threshold of effect in order to allow a safety margin in any individual patient and to ensure that there will be a satisfactory outcome improvement in symptoms from the blood transfusion. The transfusion target however need not be within the normal range. The degree of abnormality which an individual patient can sustain once laboratory results begin to shift from the normal range until it reaches the threshold of effect is called the functional reserve for that particular patient. Functional reserve is due to a compensatory mechanism such as increased cardiac output increased red cell 2 3 diphosphoglyceric acid etc. These concepts are of importance in making appropriate clinical decisions with regard to the transfusion of individual patients. Applying these concepts to platelet transfusions is as follows As the platelet count drops slightly below the normal range of 140 x 109 L clinical bleeding will not occur and the count may decrease to 30 x 109 L or lower before an increased risk of minor spontaneous clinical hemorrhage becomes evident threshold . However the transfusion trigger . the decision to transfuse platelets will be much lower than the 30 x 109 L . for example 10 x 109 L. Once a decision is made to transfuse the dose of platelets should result in a 20-40 x 109 L increase in the platelet count . the transfusion target will be beyond threshold of effect. It can be seen therefore from this example that the functional reserve in platelets is very large and extends well into the abnormal range. A further change in immune thrombocytopenic purpura ITP 110 Clinical Transfusion Medicine 26 is that the platelets are larger Chapter 22 . Therefore in this condition even very low platelet
