MedWire News: Patients who develop immunoglobulin (Ig)G antibodies to the platelet factor (PF)4/heparin complex following total knee (TKA) or hip arthroplasty (THA) have an increased risk for deep vein thrombosis (DVT), Japanese researchers report.
This finding is especially true for patients who receive unfractionated heparin (UFH), note Kiyoshi Migita (NHO Nagasaki Medical Center, Japan) and colleagues.
The researchers explain that the generation of anti-PF4/heparin antibodies following surgery - a phenomenon known as seroconversion - can cause platelet activation and aggregation, which may eventually progress to heparin-induced thrombocytopenia (HIT) and thrombosis.
In the present study, they determined the rate of IgG-class anti-PF4/heparin seroconversion and its effect on venous thromboembolism (VTE) in 374 Japanese patients undergoing THA or TKA.
The team used an IgG-specific enzyme immunoassay to measure levels of IgG anti-PF4/heparin antibodies in blood samples taken from the patients before the operation and on postoperative day 7.
They found that 74 patients seroconverted to IgG anti-PF4/heparin positivity following the operation, and the rate of seroconversion was significantly higher in TKA patients (27.5%; 44 of 160) compared with THA patients (14.0%; 30 of 214).
In addition, the rate of seroconversion was significantly higher among patients who received thromboprophylaxis with UFH (32.7%) compared with those who received low molecular weight heparin (LMWH; 9.5%) or fondaparinux (14.8%).
The researchers report that DVT occurred in 21 (9.8%) THA patients and 35 (21.9%) TKA patients, giving an overall group DVT rate of 15.0%. No cases of pulmonary embolism were observed and no patients developed HIT, despite elevated platelet counts on post-operative day 7.
Multivariate analysis adjusted for age, gender, and type of surgery, indicated that seroconversion to IgG anti-PF4/heparin positivity was a significant and independent risk factor for symptomatic DVT.
When the patients were grouped according to the type of anticoagulation they received, the researchers noted that seroconversion was associated with a 6.2-fold increased risk for DVT, relative to no seroconversion, among patients receiving UFH, but was not associated with DVT among patients treated with LMWH or fondaparinux.
Writing in the journal BMC Musculoskeletal Disorders, Migita and co-authors conclude that "seroconversion of IgG-class PF4/heparin antibodies can be associated with DVT even in the absence of thrombocytopenia, in a subset of patients undergoing total joint arthroplasty."
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