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Original Research: Antithrombotic Therapy |

The Role for Optical Density in Heparin-Induced ThrombocytopeniaOptical Density: A Cohort Study

Chee M. Chan, MD, MPH, FCCP; Christian J. Woods, MD, FCCP; Theodore E. Warkentin, MD; Jo-Ann I. Sheppard, BSc; Andrew F. Shorr, MD, MPH, FCCP
Author and Funding Information

From the Pulmonary and Critical Care Section (Drs Chan, Woods, and Shorr), MedStar Washington Hospital Center, and Georgetown University Medical Center, Washington, DC; and the Department of Pathology and Molecular Medicine (Dr Warkentin and Ms Sheppard), Hamilton Regional Laboratory Program and McMaster University, Hamilton, ON, Canada.

CORRESPONDENCE TO: Chee M. Chan, MD, MPH, FCCP, Pulmonary and Critical Care Medicine, MedStar Washington Hospital Center, 110 Irving St NW, Washington, DC 20010; e-mail: chee.m.chan@medstar.net


FOR EDITORIAL COMMENT SEE PAGE 1

FUNDING/SUPPORT: Funding support was provided by GlaxoSmithKline plc as an unrestricted grant to the MedStar Washington Hospital Center and to McMaster University.

Reproduction of this article is prohibited without written permission from the American College of Chest Physicians. See online for more details.


Chest. 2015;148(1):55-61. doi:10.1378/chest.14-1417
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BACKGROUND:  Heparin-induced thrombocytopenia (HIT) is a serious complication of heparin utilization. An enzyme-linked immunosorbent assay (ELISA) is usually performed to assist in the diagnosis of HIT. ELISAs tend to be sensitive but lack specificity. We sought to use a new cutoff to define a positive HIT ELISA.

METHODS:  We conducted a prospective observational study of hospitalized patients undergoing ELISA testing. All patients who underwent ELISA testing were eligible for inclusion (n = 496). Irrespective of the results, all subjects had confirmatory testing with a serotonin release assay (SRA). We compared a threshold optical density (OD) > 1.00 to the current definition of a positive ELISA (OD > 0.40) as a screening test for a positive SRA. We used sensitivity, specificity, and area under the receiver operating curve to determine whether an OD > 1.00 would improve diagnostic accuracy for HIT.

RESULTS:  The SRA was positive in 10 patients (prevalence, 2.0%). Adjusting the definition of a positive HIT ELISA to > 1.00 maintained the sensitivity and negative predictive value at 100% in the cohort. The positive predictive value of the higher cutoff OD was more than triple the positive predictive value of an OD > 0.40 (41.7% vs 13.3%). No patient with a positive SRA had an OD measurement ≤ 1.00.

CONCLUSIONS:  Increasing the OD threshold enhances specificity without noticeably compromising sensitivity. Altering the definition of the HIT ELISA could prevent unnecessary testing and/or treatment with non-heparin-based anticoagulants in patients with possible HIT.

TRIAL REGISTRY:  ClinicalTrials.gov; No.: NCT00946400; URL: www.clinicaltrials.gov

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