Platelet factor 4/heparin-particle gel immunoassay (PaGIA) is a weak method for heparin-induced thrombocytopenia (HIT) evaluation of post cardio-pulmonary bypass surgery patients

Comparison of polyspecific versus IgG specific ELISA in predominately cardiac patients with suspected heparin induced thrombocytopenia

A diagnosis of heparin induced thrombocytopenia (HIT) must often be made based on clinical and laboratory evidence. This was a quasi-experimental study of patients admitted from June 2016 to October 2017. The primary endpoint was the incidence of false positive results in polyspecific and IgG specific enzyme-linked immunosorbent assay (ELISA); then we compared the sensitivity and specificity of each assays in predominately cardiac patients with suspected HIT. A sensitivity/specificity analysis was conducted using serotonin release assay (SRA) as the 'gold standard'. The secondary outcome measures included length of hospital stay. We identified a total of 155 patients who met the inclusion criteria. Confirmatory tests with SRA on both groups were completed; false positive result was higher in the polyspecific group when compared to the IgG group [60% vs. 5%]. The IgG specific ELISA test yielded a sensitivity of 100% and a specificity of 95% however, the polyspecific ELISA had a low yield for specificity of 24% but maintained 100% sensitivity. In the IgG specific group with HIT-, their median length of stay was halved compared to those who were HIT + ; hospital LOS in days, IQR [30 (27-81) vs. 15 (7-33) p = 0.023] and a shorter median LOS in the ICU, IQR [24 (5-47) vs. 6 (2-14); p = 0.079]. Hospital or ICU LOS was the same in both (HIT+ and HIT-) groups managed with polyspecific ELISA. The IgG specific test had few false positive results and a high sensitivity score. Ensuring appropriate testing can bring a substantial decrease in drug expenditure, reduced length of stay and prevent unnecessary anticoagulation.

The use of flow cytometry in the diagnosis of heparin-induced thrombocytopenia (HIT)

Heparin-induced thrombocytopenia (HIT) affects some of the patients exposed to heparin. It is mediated by antibodies that recognize neoepitopes on platelet factor 4 (PF4)/heparin complexes. A HIT diagnosis requires both clinical and laboratory evaluation and remains a challenge. Since many patients develop antibodies in response to heparin, but only a few of them generate anti-PF4/heparin antibodies capable of activating platelets which consequently cause clinical complications, the performance of serologic assays is not enough to diagnose HIT. Functional assays can identify pathogenic antibodies capable of platelet activation, but they are more demanding and their limited availability contributes to the problem of diagnosing HIT. Restricted laboratories usually collect sera of multiple patients to perform functional assays only once or twice a week; hence, a HIT diagnosis can take several days. The use of flow cytometry appears to be a promising alternative in the confirmation of pathogenic anti-PF4/heparin antibodies. Flow cytometric assays detect either activation markers on a healthy donor's platelet surfaces or platelet derived microparticles formed after platelet incubation with a patient's serum. Flow cytometers are readily available in many clinical laboratories, so this technology introduces the possibility of an earlier HIT diagnosis. The objective of this review was to collect findings on flow cytometric HIT confirmations to the present date, and to review the currently available flow cytometric assays used in the diagnosis of HIT.

Clinical Significance of the Serotonin Release Assay and Platelet Count Monitoring After Cardiac Surgery

Heparin-induced thrombocytopenia (HIT) is one of the serious complications in patients who undergo cardiac surgery. However, there remains a major problem in diagnosing HIT because the current immunological assays for detection of HIT antibody have limitations. Furthermore, the clinical course of thrombocytopenia in this surgery makes it increasingly difficult to diagnose HIT. We investigated the relationship between platelet count and HIT antibody in 59 patients who underwent cardiac surgery using cardiopulmonary bypass (CPB). The number of postoperative HIT antibody-positive patients evaluated using enzyme-linked immunosorbent assay kit (polyanion IgG/IgA/IgM complex antibodies/antiplatelet factor 4 enhanced) was 37 (62.7%). In contrast, platelet activation by HIT antibody was evaluated using the serotonin release assay (SRA). More than 20% and 50% release of serotonin was obtained from 12 patients (20.3%) and 8 patients (13.6%), respectively. The levels of d-dimer were significantly different on postoperative day 14 between SRA-positive and SRA-negative groups; however, postoperative thrombus complication was not detected using sonography in the patients with positive serotonin release at all. After being decreased by the operation, their platelet count recovered within 2 weeks in both groups equally. In our study, although the patients were positive in the platelet activating HIT antibody assay, they remained free from thrombosis and their platelet count recovered after early postoperative platelet decrease. Therefore, in addition to the SRA, monitoring of platelet count might be still considered an indispensable factor to facilitate the prediction of HIT thrombosis prior to manifestation in the patients undergoing cardiac surgery using CPB.