Background and Objectives: Heparin is still a commonly used anticoagulant in prophylaxis and treatment of thromboembolic events. Heparin-induced Thrombocytopenia (HIT) is a life-threating adverse drug reaction of heparin. The diagnosis of HIT is made based on two important criteria, firstly clinical evaluation and secondly laboratory testing. In this comprehensive review, the authors will emphasize the risk factors, clinical presentation, pathophysiology, diagnostic principals and treatment of HIT. Materials and Methods: Our study method was based on the search in the PubMed Database by related key words like: "heparin", "heparin induced Thrombocytopenia", "pathophysiology", "diagnosis" and “ treatment” published during 1997 to 2018. Results: The disease is still a life-threatening event caused by the creation of an antibody against the heparin-PF4 complex and, if platelets are activated, can lead to thrombotic events in patients. Laboratory diagnostic methods are important in excluding or confirming the diagnosis of HIT, especially in patients who are moderate or highly clinical probability of HIT suspected. Conclusions: Today, with a better understanding of the pathophysiology of the disease as well as the advances made in the speed and precision of laboratory diagnostic methods, an important development has occurred in the diagnosis of HIT.

The normal range of the platelet count in fetal life is similar to that seen in adulthood , being in the ang 150-400 x109/l.neonatal Thrombocytopenia, defined as a platelet count of <150 x109/l is common, with a reported frequency of approximately 0.9% in unselected newborns, and 40% in infants in intensive care units.those arising on a background of an established genetic defect (inherited Thrombocytopenia); Those associated with birth (congenital Thrombocytopenia).Inherited ThrombocytopeniaWiskott_aldrich syndrome, amegakaryocytic Thrombocytopenia and Thrombocytopenia with absent radii(TAR) where the platelet count is usually very low;Bernard-soulier and chediak –higashi syndrome where there is a marked platelet dysfunction. Disorders with dysfunctional platelets GPIb-V-IXcomplex, Bernard-soulier syndrome, Pseudo-von willebrand disease, Type2B von willebrand,s disease, Montreal platelet syndrome, Gray platelet syndrome, Paris-trousseau syndrome, Wiskott-Aldrich syndrome, Wiskott-aldrich syndrome variants (x-linked Thrombocytopenia) Disorders without dysfunctional plateletsMay-hegglin anomaly, Alport, s syndrome, Fechtner, s syndrome, Sebastian platelet syndrome, Amegakaryocytic Thrombocytopenia, Fanconi, anemia, Trisomy syndromes, Pure genetic ThrombocytopeniaCongenital ThrombocytopeniaImmune Thrombocytopenia, Neonatal alloimmune Thrombocytopenia, Maternal autoimmune Thrombocytopenia, Intrauterine infections (TORCH syndromes)Toxoplasmosis, Congenital rubella, Cytomegalovirus, Herpes simplex, Other causes:Estimates of the rates of HIV transmission from mother to newborn range from 20 to 60% depending on the study, Maternal pre-eclampsia, Maternal use of drugs.

A case of alloimmune Thrombocytopenia in a male newborn who presented with cutaneous petechiae and purpura is reported. He had isolated Thrombocytopenia and good general condition. The platelet antigenic study of the parents was compatible with the diagnosis. Other investigations were normal. Platelet level reached to normal after treatment with intravenous immunoglobulin G (IVIG). Review of literature revealed that incidence of this disorder is one in 4000-5000 live births.