The laboratory diagnosis of heparin-induced thrombocytopenia (HIT) relies on the demonstration of antibodies to the heparin-platelet factor 4 (H-PF4) complex. Assays are based on the functional ability of H-PF4 antibodies to activate platelets, or detect the antibody directly by immunological methods. Multiple assays in each category are currently in clinical use and newer, rapid immunological assays are becoming available. The aim of this study was to compare available methods for detecting H-PF4 antibodies in a prospective study of patients with clinically suspected HIT. Functional assessment included serotonin release assay (SRA) and lumi-aggregometry (LA). Immunological assessment included ELISA (GTI), and particle gel immunoassay (PGIA; Diamed and Akers). Circulating platelet microparticles (PMP) were assessed by flow cytometry. Patients were also assessed for the pre-test probability of HIT using the Warkentin 4-T scoring system. 151 patients were enrolled. 54/151 patients (35.8%) had a positive GTI ELISA, while 53/151 (35.1%) and 39/151 (25.8%), respectively, had positive Akers and Diamed PGAI tests. Only 15/149 (10.1%) patients had a positive SRA, while only 5/150 (3.3%) gave a positive result by lumi-aggregometry. There was a strong correlation between the ELISA OD values obtained in serum and plasma using both fresh (r=0.98) and frozen (r=0.99) samples, although slightly more positive results were obtained using serum. Differences were only seen with OD values around the cut-off of 0.4. The majority (77.8%) of H-PF4 antibodies detected by ELISA were neutralized by heparin in the ‘confirmatory’ procedure. Weak antibodies (OD 0.4–0.5) were more likely to be non-neutralizable (5/12; 42%) than strong antibodies (OD>1.0; 4/23; 17%). 47 patients positive by ELISA were retested to determine the predominant immunoglobulin subclass. 15/47 (32%) were positive (OD>0.4) for IgG; 27/47 (57%) for IgM, and 12/47 (25%) for IgA. The Diamed assay more closely correlated with the GTI ELISA than the Akers test (82.1% vs. 56.7%, respectively). The PGIAs were only moderately correlated with each other (64%) with the Akers assay giving more “false positive” results relative to the ELISA. PMP were higher in patients with a positive ELISA (6.2 vs 4.7 × 106/ml) or positive SRA (5.5 vs. 5.1 ×106/ml) but this was not statistically significant due to the wide range of results. Of 119 patients assessed, 87 had a low pre-test probability of HIT (4-T score 0–3), 27 had an intermediate probability (4–5), and 5 had a high probability (6–8). The GTI ELISA was positive in 24, 56 and 80% of low, intermediate and high probability cases. The Akers PGIA was positive in 39, 41 and 40% respectively; the Diamed assay in 21, 33 and 40%, and the SRA in 7, 11 and 40%, respectively. This study was conducted in a patient population biased towards cardiovascular surgery, and confirms previously reported observations that immunoassays are more frequently positive than functional assays. The ELISA correlated better than the PGIA tests with the pre-test probability of HIT, although the Diamed test showed acceptable correlation with the ELISA. In contrast, the Akers assay correlated poorly with the ELISA, often producing positive results when the latter test was negative. We conclude that while the PGIA tests are rapid and convenient, further studies are needed to determine the basis for disparate results relative to the widely used ELISA.
It is imperative to maintain normal blood flow to provide adequate oxygen supply to specific organs and cells, as well as for the removal of metabolic byproducts. Therefore, any situation that results in blood clotting can injure or kill living tissues. In this paper, we describe a case where a protein C deficient subject who would, by all medical indicators, be at 100 % risk of experiencing thrombophlebitis, deep vein thrombosis, and or lung emboli, is able to escape all pathologies by using perioperative zymogen protein C (ZPC). This protein C deficient patient has a long history of blood clotting, particularly from surgical procedures. The patient is 81 years old and first experienced clotting due to hernia surgery in 1964, when he was hospitalized for 16 days post-surgery with life threatening complications. It was later determined in 1980, after many episodes, that the patient had hereditary protein C deficiency at the 38 % level. In his hernia surgery, perioperative ZPC was used along with accepted anticoagulation procedures with no blood clots or other related side effects occurring. This procedure can greatly benefit protein C deficient patients, and could potentially find use for non-PC deficient patients in surgeries and a variety of other medical treatments. This particular case helps to validate the importance of ZPC in effecting safer surgery in high-risk patients. It also supports the mechanism of ZPC acting as an anticoagulant without causing bleeding. Most importantly, each clinical case study represents a unique combination of surgeon, hematologist, medical staff, and patient functioning as a coordinated team. In this case, smaller amounts of very expensive ZPC achieved safe and efficacious results, which is hugely important for future clinical applications when considering the production cost of ZPC. More studies must be done to establish minimum dosing while achieving safe and efficacious outcomes.
Heparin is widely used to treat patients that present with acute coronary syndromes (ACS). A significant, albeit under-recognized complication of heparin therapy is heparin-induced thrombocytopenia (HIT), which is estimated to occur in 1–3% of patients. A significantly higher proportion (20–50%) of patients undergoing cardiac surgery and other invasive cardiology procedures develop an antibody against the heparin-platelet factor 4 (HPF4) complex. Most patients remain asymptomatic, but are nevertheless at risk for HIT with subsequent heparin exposure. Patients with severe coronary artery disease frequently have multiple hospital admissions, and heparin exposures. HPF4 antibodies are transient, and most will become undetectable three months after their initial formation. Therefore, patients with a recent history of hospitalization would be at greater risk of HIT on heparin re-exposure. We tested this hypothesis in a prospective study of patients with ACS presenting to the Emergency Department. We studied 230 patients presenting to the ED with ACS. Patients were stratified into Group 1 (having a recent [<6 months] history of hospital admission), or Group 2 (having a more remote [or no] history). Plasma samples were tested for HPF4 antibodies with a commercially available ELISA and positive samples were re-tested with a serotonin release assay (SRA). Sixteen patients (7.0%) tested positive for HPF4 antibodies by ELISA. Group 1 subjects had a higher incidence of HPF4 antibodies (10.7%) than Group 2 patients (3.2%). Of the 16 patients positive by ELISA, 14 were also tested by SRA. Of these, 7 were positive, 6 were negative and 2 gave borderline results. We conclude that approximately 7% of all patients presenting with acute coronary syndromes have a pre-existing HPF4 antibody. The incidence of a positive test is tripled in patients that have been recently hospitalized with high probability of recent heparin exposure. A significant proportion of these patients has a functionally active HPF4 antibody, which would presumably carry a higher risk of clinical HIT if re-exposed to heparin therapy for ACS and subsequent cardiovascular procedures. Our data suggest that high-risk individuals can be identified on a history of recent hospital admissions, and should receive a non-heparin anticoagulant, e.g. a direct thrombin inhibitor, until their HPF4 antibody status can be established.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.