These studies suggest that IVIg treatment should be considered in patients with HIT who have severe disease that is refractory to standard therapies.

BACKGROUND: Almost without exception, patients with heparin-induced thrombocytopenia/ thrombosis (HIT) have antibodies that recognize platelet factor 4 (PF4) in a complex with heparin; however, many heparin-treated patients without HIT are also antibody-positive. A platelet activation test, the serotonin release assay (SRA), is useful for identifying a subset of antibodies that are platelet-activating and most likely to cause HIT. However, this "gold standard" assay for HIT diagnosis is technically demanding and is routinely available only through referral laboratories, limiting its availability for timely diagnosis and management.

Key Points Platelet-activating, but not nonactivating, human HIT antibodies bind to and activate PF4-treated platelets. Activating antibodies may recognize subtle conformational changes induced in PF4 by chondroitin-4-sulfate, the major platelet glycosaminoglycan.

Integrating ECM materials in microfluidics for 3D cell culture.

Heparin-induced thrombocytopenia (HIT) is a dangerous complication of heparin therapy. HIT diagnosis is established by recognizing thrombocytopenia and/or thrombosis in an affected patient and from the results of serological tests such as the platelet factor 4 (PF4)/heparin immunoassay (PF4 ELISA) and serotonin release assay (SRA). Recent studies suggest that HIT antibodies activate platelets by recognizing PF4 in a complex with platelet glycosaminoglycans (and/or polyphosphates) and that an assay based on this principle, the PF4-dependent P-selectin expression assay (PEA), may be even more accurate than the SRA for HIT diagnosis. Here, we demonstrate that the PEA detected pathogenic antibodies before the SRA became positive in two patients with HIT studied serially, in one case even before seropositivity in the PF4 ELISA. In one of the patients treated with plasma exchange, persistent dissociation between the PEA and SRA test results was observed. These results support a role for the PEA in early HIT diagnosis.

No abstract

Heparin-induced thrombocytopenia (HIT) is a life-threatening, pro-thrombotic, antibody-mediated disorder. To maximize the likelihood of recovery, early and accurate diagnosis is critical. Widely available HIT assays such as the Platelet Factor 4-Heparin ELISAs lack specificity, and the "gold standard" C14-labeled serotonin release assay (SRA) is of limited value for early patient management due to availability only through reference laboratories. Recent studies demonstrate that "pathogenic" HIT antibodies selectively activate PF4-treated platelets and that a technically simpler assay, the PF4-dependent P-selectin Expression Assay (PEA), may provide an option for rapid and conclusive results. Four hundred and nine consecutive adults suspected of HIT were classified as disease-positive, -negative or -indeterminate based upon predefined criteria that combined 4Ts scores and HIT ELISA results. Patients deemed "HIT-indeterminate" were considered disease-negative in the primary analysis and disease-positive in a sensitivity analysis. The ability of PEA and SRA to identify patients judged to have HIT was compared using receiver operating characteristic curve statistics. Using these predefined criteria, the diagnostic accuracy of PEA was high (Area under the curve [AUC] of 0.94; 0.87-1.0, 95% CI) and similar to that of SRA (0.91; 0.82-1.0, 95% CI). In sensitivity analysis, the AUCs of PEA and SRA were also similar at 0.88 (0.78-0.98, 95% CI) and 0.86 (0.77-0.96, 95% CI), respectively. The PEA, a technically simple non-radioactive assay that uses ~20-fold fewer platelets compared to the SRA had high accuracy for diagnosing HIT. Widespread use of the PEA may facilitate timely and more effective management of patients with suspected HIT.

No abstract