Heparins platelet

Heparin-induced thrombocytopenia A clinical syndrome of IgG antibody production against the heparin-platelet factor 4 complex occurring in approximately 1% to 5% of patients exposed to either heparin or low-molecular-weight heparin. Heparin-induced thrombocytopenia results in excess production of thrombin, platelet aggregation, and thrombocytopenia (due to platelet clumping), often leading to venous and arterial thrombosis, amputation of extremities, and death. 

The following points should be considered in all patients receiving heparin Platelet counts should be performed frequently thrombocytopenia appearing in a time frame consistent with an immune response to heparin should be considered suspicious for HIT and any new thrombus occurring in a patient receiving heparin therapy should raise suspicion of HIT. Patients who develop HIT are treated by discontinuance of heparin and administration of a direct thrombin inhibitor or fondaparinux (see below). 

The second type of heparin-induced thrombocytopenia is severe and may be associated with a platelet count below 100,000/mm and thrombosis. ° ° The platelet count generally begins to decline 5 to 10 days after the start of heparin therapy (sooner in patients previously treated with heparin). Thrombocytopenia and thrombosis may develop with low-dose heparin, heparin-coated catheters, or even heparin flushes. Historically, the reaction was thought to be mediated by the formation of antibodies to the platelet-heparin complex. However, evidence suggests a complex interaction between heparin, platelet factor 4 (PF4), platelet membrane Fc receptors, and possibly heparin-like molecules on the surface of endothehal cells (Fig. 102-6). Circulating heparin reacts with PF4 to produce a... 

Mullen MP, Wessel DL, Thomas KC, Gauvreau K, Neufeld EJ, McGowan Jr. FX, Dinardo JA. The incidence and implications of anti-heparin-platelet factor 4 antibody formation in a pediatric cardiac surgical population. Anesth Analg 2008 107(2) 371-8. 

Gerdsen F, Luxembourg B, Langer F, Bauersachs R, Lindhoff-Last E. A prospective analysis of heparin-platelet factor 4 antibodies in pregnant women treated with the low-molecular-weight heparin, dalteparin. Blood Coagul Fibrinolysis 2008 19(6) 477-81. 

Successful use of bivalirudin for combined carotid endarterectomy and coronary revascularization with the use of cardiopulmonary bypass in a patient with an elevated heparin-platelet factor 4 antibody titer. Anesth Analg 2009 108(4) lllT-5. 

Periodic platelet counts, hematocrit, and tests for occult blood in die stool should be performed throughout die entire course of heparin therapy. 

A complete blood count, platelets, and stools for occult blood may be ordered periodically throughout therapy. Thrombocytopenia may occur during heparin administration. A mild, transient thrombocytopenia may occur 2 to 3 days after heparin therapy is begun. This early development of thrombocytopenia tends to resolve itself despite continued tiierapy. The nurse reports a platelet count of less than 100,000 mm3 immediately because die primary care provider may choose to discontinue die heparin therapy. 

A number of laboratory tests are available to measure the phases of hemostasis described above. The tests include platelet count, bleeding time, activated partial thromboplastin time (aPTT or PTT), prothrombin time (PT), thrombin time (TT), concentration of fibrinogen, fibrin clot stabifity, and measurement of fibrin degradation products. The platelet count quantitates the number of platelets, and the bleeding time is an overall test of platelet function. aPTT is a measure of the intrinsic pathway and PT of the extrinsic pathway. PT is used to measure the effectiveness of oral anticoagulants such as warfarin, and aPTT is used to monitor heparin therapy. The reader is referred to a textbook of hematology for a discussion of these tests. 

Anticoagulant or heparin use <48 h before onset with elevated partial-thromboplastin time Prothrombin time >15 s Platelet count <100,000/mm ... 

Unfractionated heparin Bleeding, heparin-induced thrombocytopenia Clinical signs of bleeding3 baseline CBC and platelet count aPTT every 6 hours until target then every 24 hours daily CBC platelet count every 2 days (minimum, preferably every day)... 

Heparin-induced thrombocytopenia (HIT) is a very serious adverse effect associated with UFH use. Platelet counts should be monitored every 2 to 3 days dining the course of UFH therapy.5 HIT should be suspected if the platelet count drops by more than 50% from baseline or to below 120,000. In patients with contraindications to anticoagulation therapy, UFH should not be administered (Table 7-7). 

The incidence of HIT is lower with LMWHs than with UFH. However, LMWHs cross-react with heparin antibodies in vitro and should not be given as an alternative anticoagulant in patients with a diagnosis or history of HIT.5 Monitor platelet counts every few days during the first 2 weeks and periodically thereafter.5... 

If the patient is treated with UFH or LMWH and platelet count has dropped by more than 50% from baseline or is less than 120x1 OVjil, evaluate the patient for heparin-induced thrombocytopenia (HIT). 

Known bleeding diathesis, including but not limited to (1) platelet count less than 100 x 1 0 /mm3 (100 x 109/L) (2) heparin within 48 hours with an elevated aPTT or (3) current oral anticoagulant use (e.g., warfarin) or recent use with an elevated PT (greater than... 

Mayo KH, Ilyina E, Roongta V, et al. Heparin binding to platelet factor-4. An NMR and site-directed mutagenesis study arginine residues are crucial for binding. Biochem J 1995 312 357-65. 

Stuckey JA, St Charles R, Edwards BF. A model of the platelet factor 4 complex with heparin. Proteins 1992 14 277-87. 

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