Pathogenic PF4/Polyvinylsulfonate ELISA-negative Antibodies in HIT

Area of Science:

• Immunology
• Hematology
• Clinical Pathology

Background:

• Platelet factor 4-polyanion enzyme-linked immunosorbent assays (ELISAs) are standard for diagnosing heparin-induced thrombocytopenia (HIT).
• Current guidelines use ELISA-negative results to exclude HIT, leading to cessation of alternative anticoagulants and potential heparin reintroduction.
• This practice may pose risks for patients with ELISA-negative HIT.

Purpose of the Study:

• To investigate the existence and clinical significance of ELISA-negative HIT.
• To characterize the antibodies responsible for ELISA-negative HIT.
• To evaluate the safety of heparin re-exposure in ELISA-negative HIT patients.

Main Methods:

• Utilized antigen-based and PF4-dependent functional testing to study ELISA-negative platelet-activating antibodies.
• Screened ELISA-negative patients and mice immunized with PF4/heparin.
• Assessed antibody-dependent platelet activation, FcγRIIa receptor involvement, and heparin inhibition.

Main Results:

• Identified three HIT-suspected patients with ELISA-negative results who showed PF4-dependent platelet activation.
• Functional testing identified three additional ELISA-negative patients with HIT-consistent histories and platelet-activating antibodies.
• Five of six ELISA-negative HIT patients experienced adverse events, including thrombocytopenia and thrombosis, upon heparin re-exposure. A murine model confirmed ELISA-negative HIT antibody characteristics.

Conclusions:

• ELISA-negative HIT is a critical diagnostic consideration.
• Failure to recognize ELISA-negative HIT can lead to harmful cessation of alternative anticoagulation and unsafe heparin re-exposure.
• Accurate diagnosis and management are essential to prevent adverse outcomes in these patients.