Utilization of 4T score to determine the pretest probability of heparin-induced thrombocytopenia in a community hospital in upstate New York

Clinical decision support to reduce unnecessary diagnostic testing for heparin-induced thrombocytopenia

Appropriate evaluation of heparin-induced thrombocytopenia (HIT) is imperative because of the potentially life-threatening complications. However, overtesting and overdiagnosis of HIT are common. Our goal was to evaluate the impact of clinical decision support (CDS) based on the HIT computerized-risk (HIT-CR) score, designed to reduce unnecessary diagnostic testing. This retrospective observational study evaluated CDS that presented a platelet count versus time graph and 4Ts score calculator to clinicians who initiated a HIT immunoassay order in patients with predicted low risk (HIT-CR score 0-2). The primary outcome was the proportion of immunoassay orders initiated but cancelled after firing of the CDS advisory. Chart reviews were conducted to assess anticoagulation usage, 4Ts scores and the proportion of patients who had HIT. In a 20-week period, 319 CDS advisories were presented to users who initiated potentially unnecessary HIT diagnostic testing. The diagnostic test order was discontinued in 80 (25%) patients. Heparin products were continued in 139 (44%) patients, and alternative anticoagulation was not given to 264 (83%). The negative predictive value of the advisory was 98.8% (95% CI: 97.2-99.5). HIT-CR score-based CDS can reduce unnecessary diagnostic testing for HIT in patients with a low pretest probability of HIT.

Reducing Inappropriate Simultaneous Ordering of Heparin Antibody and Serotonin Release Assays

INTRODUCTION

A 4T score with intermediate or high probability of heparin-induced thrombocytopenia prompts ordering of anti-platelet 4 heparin complex. If positive, a serotonin release assay (SRA) is recommended to confirm diagnosis. Despite these recommendations, overtesting of both anti-platelet 4 and SRA is highly prevalent.

METHODS

This was a quality improvement initiative using two forms of clinical decision support across 11 acute care hospitals. First, a 4T calculator was incorporated into anti-platelet 4 orders. Second, a Best Practice Advisory fired when anti-platelet 4 and SRA were ordered simultaneously, prompting the provider to remove the SRA order. Data were analyzed by a quasi-experimental interrupted time series linear regression comparing weekly average laboratory tests per 1,000 patient-days pre- and postintervention.

RESULTS

Average ordering frequency of anti-platelet 4 changed from 0.508 to 0.510 per 1,000 patient-days (0.5%, p = 0.42) without significant slope or level differences. Average ordering frequency of SRA decreased from 0.430 to 0.289 per 1,000 patient-days (32.8%, p < 0.001) with a significant level difference of -0.128 orders per 1,000 patient-days (-31.2%, p < 0.05).

CONCLUSION

A simultaneous Best Practice Advisory was effective in reducing SRA orders, but not anti-platelet 4 orders.

Early Suspicion of Heparin-Induced Thrombocytopenia for Successful Free Flap Salvage: Reports of Two Cases

Heparin-induced thrombocytopenia (HIT) is an underestimated complication of heparin treatment. Flap loss and related morbidity (even mortality) are caused by occlusion of the capillary vessels by a highly immunogenic complex formed by adherence of antiheparin antibodies to platelet factor 4. Early suspicion and effective treatment of HIT developing in two free flaps are described. We report on the management of two patients with HIT. Both patients were treated successfully by early suspicion and hematology consultation. Heparin products were discontinued; the patients were switched to a nonheparin anticoagulant. We emphasize the importance of early diagnosis, hematologist assessment, and a change to a nonheparin anticoagulant to prevent flap failure and possibly the catastrophic consequences of such failure.

Prospective evaluation of heparin-induced thrombocytopenia expert probability and 4T scores in Chinese patients with suspected heparin-induced thrombocytopenia

Supplemental Digital Content is available in the text

Background

Diagnosis of heparin-induced thrombocytopenia (HIT) is challenging. This study aimed to compare the diagnostic performance of HIT expert probability (HEP) and 4T scores, and to evaluate the inter-observer reliability for the 4T score in a clinical setting.

Methods

This prospective study included HIT-suspected patients between 2016 and 2018. Three hematologists assessed the HEP and 4T scores. Correlations between scores and anti-platelet factor 4 (anti-PF4)/heparin antibodies were evaluated. Receiver operating characteristic curves and area under the curve (AUC) were used to assess the predictive accuracy of these two scoring models. The intraclass correlation coefficient (ICC) was used to assess the inter-observer agreement of 4T scores between residents and hematologists.

Results

Of the 89 subjects included, 22 (24.7%) were positive for anti-PF4/heparin antibody. The correlations between antibody titer and either HEP or 4T scores were similar (r = 0.392, P < 0.01 for the HEP score; r = 0.444, P < 0.01 for the 4T score). No significant difference in the diagnostic performance was displayed between these two scores (AUC for the HEP score: 0.778 vs. AUC for the 4T score: 0.741, P = 0.357). Only 72 4T scores were collected from the residents, with a surprisingly low percentage of observers (43.1%) presenting the four individual item scores which made up their 4T score. The AUC of 4T score assessed by residents and hematologists was 0.657 (95% confidence interval [CI]: 536–0.765) and 0.780 (95% CI: 0.667–0.869, P < 0.05), respectively. The ICC of 4T score between residents and hematologists was 0.49 (95% CI: 0.29–0.65, P < 0.01), demonstrating a fair inter-observer agreement.

Conclusions

The HEP score does not display a better performance for predicting HIT than the 4T score. With the unsatisfactory completion rate, the inter-observer agreement of 4T score in a tertiary hospital is fair, underscoring the necessity for continuing education for physicians.

Implementation of a rapid HIT immunoassay at a university hospital - Retrospective analysis of HIT laboratory orders in patients with thrombocytopenia

BACKGROUND

Heparin-induced thrombocytopenia (HIT) is a rare cause of thrombocytopenia and a potentially life-threatening adverse drug reaction. Clinical overdiagnosis of HIT results in costly laboratory tests and anticoagulation. Criteria and algorithms for diagnosis are established, but their translation into clinical practice is still challenging.

STUDY DESIGN AND METHODS

In a retrospective approach we studied all HIT related laboratory test requests within four years and evaluated data before (1st period, 24month) and after (2nd period, 24month) replacing particle gel immunoassay (PaGIA) and enzyme-linked immunosorbent assay (ELISA) by a chemiluminescent immunoassay (CLIA). HIT was confirmed by heparin-induced platelet activation (HIPA) test. Clinical pretest probability for HIT using an implemented simplified 4Ts score and platelet count were evaluated. Costs for laboratory tests and alternative anticoagulation were calculated.

RESULTS

In 1850 patients with suspected HIT, 2327 laboratory orders were performed. In 87.2% of these orders an intermediate/high simplified 4Ts score was found. Thrombocytopenia was present in 87.1%. After replacing PaGIA and ELISA by CLIA the number of immunological and functional laboratory tests was reduced by 38.2%. The number of positive HIT immunoassays declined from 22.6% to 6.0%, while the number of positive HIPA tests among positive immunological tests increased by 19%. Altogether, acute HIT was confirmed in 59 patients. A decline in the use of alternative anticoagulants was observed in the 2nd period.

CONCLUSION

Our study shows that in a university hospital setting HIT is well-known, but diagnosis requires a precise laboratory confirmation. Replacing PaGIA and ELISA by CLIA did not influence laboratory order behavior but results in reduced overall costs for laboratory diagnostics and alternative anticoagulation.