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Updated: Jul 5, 2026
PIP-on-a-chip: A Label-free Study of Protein-phosphoinositide Interactions
Published on: July 27, 2017
Quantitative interpretation of optical density measurements using PF4-dependent enzyme-immunoassays
T E Warkentin1, J I Sheppard, J C Moore
1Department of Pathology and Molecular Medicine, Michael G DeGroote School of Medicine, McMaster University, Hamilton, ON, Canada. twarken@mcmaster.ca
Background:
Many laboratories test for heparin-induced thrombocytopenia (HIT) using a PF4-dependent enzyme-immunoassay (EIA). An advantage of the EIA is its simplicity; a disadvantage is that it only indirectly detects heparin-dependent, platelet-activating antibodies ('HIT antibodies').
Objectives:
To determine whether the magnitude of a positive EIA result, expressed in optical density (OD) units, predicts risk of HIT antibodies, defined as a strong-positive platelet serotonin-release assay (SRA) result (>or=50% serotonin release).
Patients/Methods:
We determined the risk of a strong-positive SRA result for five categories of OD reactivity (<0.40, 0.40-<1.00, 1.00-<1.40, 1.40-<2.00, and >or=2.00 OD units) using two EIAs (commercial anti-PF4/polyanion IgG/A/M and in-house anti-PF4/heparin-IgG).
Results:
For patient sera investigated for HIT antibodies, a weak-positive result (0.40-<1.00 OD units) in either EIA indicated a low probability (
Conclusions:
The probability of HIT antibodies (strong-positive SRA result) inferred by a positive PF4-dependent EIA varies considerably in relation to the magnitude of the EIA result, expressed as OD values. In our laboratory, the probability of HIT antibodies being present reached >or=50% only when the OD level was >or=1.40 units.
