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Hemostasis and Thrombosis - part 4

Độ cao bị cô lập của PT chỉ mang tính cô lập của một thiếu hụt yếu tố VII. Độ cao bị cô lập của APTT thường do ô nhiễm heparin, thuốc ức chế lupus, khuyết tật bị cô lập VIII, IX, XI, hay con đường liên lạc. Nghiên cứu pha trộn có thể cung cấp thông tin để thu hẹp danh sách các chẩn đoán có thể. Kéo dài của cả hai PT và APTT cho thấy nhiều khiếm khuyết hoặc thiếu hụt các yếu tố | Acquired Bleeding Disorders 55 Table 2.4 . Isolated elevations of the PT are indicative of an isolated factor VII deficiency. Isolated elevations of the aPTT are typically due to heparin contamination lupus inhibitors isolated defects ofVIII IX XI or the contact pathway. Mixing studies can provide information to narrow the list of possible diagnoses. Prolongation of both the PT and aPTT suggests multiple defects or deficiency of factors II V or X. Marked prolongation of the PT and aPTT can also be seen with low levels of fibrinogen 50 mg dl . Patients with hematocrits of greater than 60 may have spurious elevations of the PT and aPTT due to improper plasma anticoagulant ratio in the sample tube. Further coagulation tests are ordered based on the PT and aPTT to define the defect better if the reason for the coagulation deficiency is not apparent by the history i.e. severe liver disease . Vitamin KDeficiency Vitamin K is critical in the synthesis of coagulation factors II VI IX X protein C protein S and protein Z. Patients obtain vitamin K from food sources and from metabolism of intestinal flora. Vitamin K is used as a cofactor in gammacarboxylation of the vitamin K-dependent proteins. The gammacarboxylation involves oxidation of vitamin K. Vitamin K is recycled in a step blocked by warfarin. Despite being a fat soluble vitamin body stores of vitamin K are low and the daily requirement is 1 p g kg day. Vitamin K deficiency can present dramatically. Once the body stores of vitamin K are depleted production of the vitamin K-dependent proteins ceases and the INR will increase rapidly to extreme levels. This can be seen in patients with poor nutrition who have a mildly prolonged INR going into surgery but several days post-operatively have an INR of 50. The diagnosis is suspected when there is a history of prolonged antibiotic use or malnourishment. One must also suspect vitamin K deficiency in a previously healthy patient who presents with an elevated INR that corrects