Heparin-induced thrombocytopenia (HIT) is a condition where the use of heparin, a common blood thinner, leads to a decrease in platelet count. This occurs when the body forms antibodies against a complex of heparin and a protein called platelet factor 4. As a result, the immune system mistakenly attacks the platelets, causing them to drop in number. HIT can increase the risk of blood clots, despite low platelet levels, which can lead to serious complications. It is essential for healthcare providers to monitor patients on heparin for signs of HIT and to consider alternative treatments if necessary.