D75.82 Heparin induced thrombocytopenia (HIT)

Name of the Condition

• Heparin induced thrombocytopenia (HIT) (ICD-10 Code: D75.82)

Summary

Heparin induced thrombocytopenia (HIT) is an immune-mediated adverse reaction to heparin therapy, characterized by a decrease in platelet count and an increased risk of thrombosis. It occurs when antibodies form against the heparin-platelet factor 4 complex, leading to platelet activation and potential clot formation. This condition can develop after exposure to unfractionated or low-molecular-weight heparin and requires prompt recognition to avoid complications.

Causes

HIT is caused by an immune response to heparin, typically occurring 5–14 days after initiating therapy. The reaction involves the formation of antibodies against the heparin-platelet factor 4 complex, which activates platelets and triggers a prothrombotic state. Both unfractionated heparin (UFH) and low-molecular-weight heparin (LMWH) can induce this response, though UFH is more commonly associated with HIT.

Risk Factors

Risk factors for HIT include:

• Recent exposure to heparin (within 100 days)
• Surgical procedures (e.g., cardiac, orthopedic) where heparin is used
• Prolonged heparin therapy
• History of HIT
• Female gender
• Increased body mass index

Symptoms

Symptoms of HIT may include:

• Sudden drop in platelet count (typically >50% reduction)
• New or worsening thrombosis (e.g., deep vein thrombosis, pulmonary embolism)
• Skin lesions at heparin injection sites
• Fever
• Chills
• Tachycardia

Diagnosis

Diagnosis of HIT involves clinical assessment and laboratory testing. A high pretest probability (e.g., using the 4T score) is followed by confirmatory tests, such as enzyme-linked immunosorbent assay (ELISA) for heparin-platelet factor 4 antibodies or functional assays (e.g., serotonin release assay). Imaging may be used to detect thrombosis if clinically suspected.

Treatment Options

Treatment focuses on discontinuing heparin and initiating alternative anticoagulation. Direct thrombin inhibitors (e.g., argatroban) or factor Xa inhibitors (e.g., fondaparinux) are preferred. Platelet transfusions are generally avoided unless active bleeding or urgent procedures are required. Supportive care includes monitoring for thrombotic complications.

Prognosis and Follow-Up

With prompt treatment, the prognosis for HIT is generally favorable, but thrombotic events can occur in 20–50% of cases if untreated. Follow-up includes monitoring platelet counts and assessing for recurrent thrombosis. Long-term management may involve avoiding heparin and using alternative anticoagulants for future procedures.

Complications

Complications of HIT include:

• Venous or arterial thrombosis (e.g., stroke, myocardial infarction)
• Heparin-induced skin necrosis
• Thrombotic microangiopathy
• Rarely, disseminated intravascular coagulation (DIC)

Lifestyle & Prevention

Prevention involves minimizing unnecessary heparin use and using alternative anticoagulants when possible. Patients with a history of HIT should avoid heparin and inform healthcare providers of their condition. Vigilant monitoring of platelet counts during heparin therapy is recommended for early detection.

When to Seek Professional Help

Seek immediate medical attention if symptoms of HIT develop, such as unexplained bruising, swelling, or pain, especially after heparin exposure. Prompt evaluation is critical to prevent life-threatening thrombosis.

Tips for Medical Coders

When coding D75.82, ensure documentation confirms the diagnosis of heparin induced thrombocytopenia, including the temporal relationship to heparin exposure and clinical findings (e.g., platelet count drop, thrombosis). Note whether the case involves type I (non-immune) or type II (immune-mediated) HIT, as coding may vary. Document any confirmatory testing (e.g., antibody assays) to support the diagnosis.