Heparin induced thrombocytopenia (HIT) is a complication of heparin therapy where platelet counts decrease. There are two types: immune-mediated HIT which can be dangerous and cause clots, and non-immune mediated HIT which is self-limited. Symptoms include bleeding or clots. Diagnosis involves platelet count drops and antibody tests. Treatment requires stopping heparin and using alternative anticoagulants to prevent dangerous clots. Nurses monitor patients on heparin closely for signs of HIT and intervene appropriately.