HEPARIN INDUCED THROMBOCYTOPENIA
Sherif Mohamed fahmyAbou-Elela;
Abstract
Heparin-induced thrombocytopenia (HIT), typically occurring in the second week of heparin therapy, is an antibody-mediated adverse drug reaction associated with increased thrombotic risk.
The most important antigens are located on platelet factor4 (PF4)/heparin complexes. All HIT is caused by platelet-activating antibodies, but not all PF4/ heparin-reactive antibodies cause HIT. Thus, tests have high negative, but only moderate, positive predictive value.
The diagnosis of HIT can however often be problematic, particularly in those patient populations with a high incidence of other potential reasons for thrombocytopenia. Furthermore, antibodies against PF4/heparin complexes, whether or not they are platelet activating, are much more frequent than clinical HIT. Therefore, all so -called HIT tests have a high negative predictive value and a rather low positive predictive value if not interpreted in the context of the clinical picture.
The diagnosis of HIT should be based on both the typical clinical symptoms and the detection of pathogenic HIT antibodies. In other words, HIT is a clinic-pathologic syndrome
WHEN TO SUSPECT HIT
HIT should be considered whenever a patient has unexplained thrombocytopenia.platelet counts do not usually fall below 20,000 as a consequence of HIT, and other causes (drug-induced thrombocytopenia, disseminated intravascular coagulation, immune thrombocytopenic purpura) should be suspected if the platelet count is in this range.
Postoperative patients (particularly those with long spine or other major blood loss surgeries) often have depressed platelet counts for days postoperatively, but if the platelet count fails to rebound or falls 50 % or more from a baseline value, a diagnosis of HIT should be entertained. Other red flags for HIT include:
■ Thrombosis associated with thrombocytopenia
■ Platelet count that has fallen 50 % or more from a baseline value (note that it may still be in the normal range)
■ Necrotic skin lesions at heparin injection sites
■ Prior exposure to heparin
The most important antigens are located on platelet factor4 (PF4)/heparin complexes. All HIT is caused by platelet-activating antibodies, but not all PF4/ heparin-reactive antibodies cause HIT. Thus, tests have high negative, but only moderate, positive predictive value.
The diagnosis of HIT can however often be problematic, particularly in those patient populations with a high incidence of other potential reasons for thrombocytopenia. Furthermore, antibodies against PF4/heparin complexes, whether or not they are platelet activating, are much more frequent than clinical HIT. Therefore, all so -called HIT tests have a high negative predictive value and a rather low positive predictive value if not interpreted in the context of the clinical picture.
The diagnosis of HIT should be based on both the typical clinical symptoms and the detection of pathogenic HIT antibodies. In other words, HIT is a clinic-pathologic syndrome
WHEN TO SUSPECT HIT
HIT should be considered whenever a patient has unexplained thrombocytopenia.platelet counts do not usually fall below 20,000 as a consequence of HIT, and other causes (drug-induced thrombocytopenia, disseminated intravascular coagulation, immune thrombocytopenic purpura) should be suspected if the platelet count is in this range.
Postoperative patients (particularly those with long spine or other major blood loss surgeries) often have depressed platelet counts for days postoperatively, but if the platelet count fails to rebound or falls 50 % or more from a baseline value, a diagnosis of HIT should be entertained. Other red flags for HIT include:
■ Thrombosis associated with thrombocytopenia
■ Platelet count that has fallen 50 % or more from a baseline value (note that it may still be in the normal range)
■ Necrotic skin lesions at heparin injection sites
■ Prior exposure to heparin
Other data
| Title | HEPARIN INDUCED THROMBOCYTOPENIA | Other Titles | نقص الصفائح الدموية نتيجة استخدام عقار الهيبارين | Authors | Sherif Mohamed fahmyAbou-Elela | Issue Date | 2014 |
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