1. Optical Densities Reduce Odds of Heparin-induced Thrombocytopenia Over-diagnosis 
Theodore E. Warkentin, MD 
The American Journal of Medicine 
Volume 125, Issue 1, Pages 3-4 (January 2012)
DOI: /j.amjmed
Copyright © 2012 Elsevier Inc. Terms and Conditions

2. Figure
Iceberg model of heparin-induced thrombocytopenia: higher optical density (OD) values in enzyme-immunoassays (EIAs) predict for greater frequency of platelet-activating antibodies, heparin-induced thrombocytopenia (HIT), and HIT-associated thrombosis. Clinically evident heparin-induced thrombocytopenia, comprising patients with (HIT-T) and without thrombosis, is represented by the portion of the iceberg above the waterline; the portion below the waterline represents subclinical anti-platelet factor 4 (PF4)/heparin seroconversion. Three types of assays are highly sensitive for diagnosis of heparin-induced thrombocytopenia: the platelet activation assay (eg, serotonin-release assay [SRA]), the immunoglobulin G (IgG)-specific PF4-dependent EIAs (EIA-IgG), and polyspecific EIAs that detects anti-PF4/heparin antibodies of the 3 major immunoglobulin classes (EIA-IgG/A/M). In contrast, diagnostic specificity is highest for the SRA, intermediate for the EIA-IgG, and lowest for the EIA-IgG/A/M. The approximate probability of SRA+ status and thrombosis risk—in relation to a given EIA result, expressed in units of optical density—is obtained from the literature.3,5 Presumably, the “background” thrombosis rate for an optical density <0.40 units would be close to ∼15% (not reported by Baroletti et al5).
The American Journal of Medicine  , 3-4DOI: ( /j.amjmed )
Copyright © 2012 Elsevier Inc. Terms and Conditions