Prevalence and Overtesting of True Heparin-Induced Thrombocytopenia in a 591-Bed Tertiary Care, Teaching Hospital

Abstract

Heparin-induced thrombocytopenia type II (HIT) is a rare but potentially fatal antibody-mediated reaction to all forms of heparin (unfractionated heparin, low-molecular weight heparin, heparin flushes, and heparin-coated catheters), which can lead to HIT with thrombosis. Two tests commonly used to screen for HIT include the enzyme-linked immunosorbent assay (ELISA) and serotonin release assay (SRA). This is a retrospective chart review study conducted from January 1, 2013, through December 31, 2014, to estimate the rate of true HIT in critical care patients at Winthrop-University Hospital, located in Mineola, New York. Patients are classified as positive for HIT if both ELISA and SRA immunoassays are positive. We reviewed 507 heparin immunoassays, excluding 64 who had an inappropriate ELISA test sent due to no administration of heparin, enoxaparin, or heparin lock flush at this or previous hospital stays at Winthrop. Of the 443 heparin immunoassays, ELISA results were positive for 66 patients (15.1%), and only 11 (2.5%) patients had true cases of HIT with a 95% confidence interval of 1.3% to 4.4%. The 4T score for those with true HIT (median: 5.0) was statistically higher compared to those without true HIT (median: 2.0; P < .001). Despite guidelines in place, overtesting for HIT is still a prevalent issue.

HIT-It or Quit It: Heparin-Induced Thrombocytopenia Testing Appropriateness Using 4T Scoring and Inappropriate Testing Cost Analysis

“…4 In that study, the cost of testing for patients with a low probability 4T score was US$40,591. 4 In our study, the largest proportion of tests was in low-probability patients and incurred a testing cost of US$23,617. These results reflect a wider problem with overtreatment and low-value testing, as a recent literature review estimated that these issues incur a "waste" cost of between $75.7 and $101.2 billion in the United States annually.…”

“…In the diagnosis of HIT, the HIT Ab is generally more widely available and faster than the more specific and sensitive SRA. 4 For this reason, the HIT Ab is used to screen for HIT and SRA is used to confirm a positive HIT Ab. The HIT Ab can return false positives in patients with other antibody-mediated diseases, such as SLE, however, and therefore should be evaluated in conjunction with a patient's clinical picture.…”

“…6 In a 2012 meta-analysis, the 4T scoring system had a 99.8% negative predictive value for patients with a score of ≤3. 4 The American Society of Hematology recommends against testing patients with a low pretest probability for HIT based on 4T scoring, as well as refraining from discontinuing heparin or starting non-heparin anticoagulants in these patients, because this often increases a patient's risk of bleeding and healthcare costs. 7 It is possible for a falsely low score to be calculated based on missing platelet values or coexisting conditions that also may cause thrombocytopenia.…”

Thrombosis with Thrombocytopenia Syndrome After Administration of AZD1222 or Ad26.COV2.S Vaccine for COVID-19: A Systematic Review

“…This can be attributed to the higher cost, turnaround time, and resource intensiveness associated with SRAs, limiting their use in most settings around the globe. 86 While the sensitivity and specificity of SRAs and ELISA have not been compared in TTS patients, evidence extrapolated from HIT suggests that SRAs, however, could potentially be helpful in patients with negative or equivocal ELISA findings but strong suspicion of TTS, owing to their greater specificity in HIT. 87 However, this necessitates further investigations, considering that patients with negative ELISA results were excluded from this review.…”

Anticoagulation strategies in extracorporeal circulatory devices in adult populations

“…HIT is classified as type I (non‐antibody‐mediated reaction to heparin) or type II (antibody‐mediated reaction against heparin‐platelet factor 4 complex). HIT type II is more severe and leads to platelet activation and an increased risk of thrombosis 16 . HIT is commonly associated with both venous and arterial thrombosis, leading to skin necrosis, limb gangrene, and organ ischemia 17 .…”