Diagnosing Heparin-Induced Thrombocytopenia

Educational Objectives

Summary

Diagnosing Heparin-Induced Thrombocytopenia: How Accurate Is the Recommended Algorithm?

Heparin-induced thrombocytopenia (HIT) is a high-risk condition that requires immediate therapy with high-risk medications; thus, accurate diagnosis is critical. Because HIT-antibody testing has a relatively high false-positive rate, guidelines direct clinicians to use an algorithm that starts with the 4Ts score (https://www.mdcalc.com/calc/1787/4ts-score-heparin-induced-thrombocytopenia) and then recommend antibody testing in patients whose 4Ts scores indicate intermediate or high risk for HIT. In a prospective study of 1300 patients with possible HIT, investigators assessed the accuracy of the 4Ts score and the guideline-recommended diagnostic algorithm. The reference-standard test for comparison was a heparin-induced platelet activation assay; prevalence of HIT was 8.4% by reference-standard testing. Findings appear in JAMA Network Open (https://doi.org/10.1001/jamanetworkopen.2024.3786).

Positive predictive values of 4Ts score and the recommended diagnostic algorithm were expectedly low (15% and 66%, respectively). However, nearly half of patients were low risk using 4Ts score and would not have warranted antibody testing by the recommended diagnostic algorithm. That algorithm had high sensitivity (87%) and specificity (96%) and a very high negative predictive value (99%).

Because clinicians order reference-standard testing (i.e., serotonin release assay or heparin-induced platelet activation assay) to confirm positive HIT-antibody testing, false positives by the recommended algorithm eventually get resolved. However, 9% of patients with confirmed HIT (10 of 111) had false-negative (i.e., “low-risk”) 4Ts scores in this study. Additional testing still should be considered if suspicion for HIT remains despite a low-risk 4Ts score; for example, a score of 3 points is technically “low risk” but might warrant further testing based on clinical gestalt.

Daniel D. Dressler, MD, MSc, MHM, FACP

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Acknowledgements

CME/CE INFO

Accreditation:

The Audio- Digest Foundation is accredited by the Accreditation Council for Continuing Medical Education to provide continuing medical education for physicians.

The Audio- Digest Foundation designates this enduring material for a maximum of 0.00 AMA PRA Category 1 Credits™. Physicians should claim only the credit commensurate with the extent of their participation in the activity.

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Lecture ID:

JW350919

Expiration:

This CME course qualifies for AMA PRA Category 1 Credits™ for 3 years from the date of publication.

Instructions:

To earn CME/CE credit for this course, you must complete all the following components in the order recommended: (1) Review introductory course content, including Educational Objectives and Faculty/Planner Disclosures; (2) Listen to the audio program and review accompanying learning materials; (3) Complete posttest (only after completing Step 2) and earn a passing score of at least 80%. Taking the course Pretest and completing the Evaluation Survey are strongly recommended (but not mandatory) components of completing this CME/CE course.

Estimated time to complete this CME/CE course:

Approximately 2x the length of the recorded lecture to account for time spent studying accompanying learning materials and completing tests.

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