Jean Amiral: Laboratory differentiation of HIT, VITT and PF4 dependent Thrombocytopenias
Jean Amiral, Hemostasis IVD Expert, Founder of HYPHEN BioMed and Consultant at SH-Consulting, shared a post on LinkedIn:
“Laboratory differentiation of HIT, VITT, and PF4 dependent Thrombocytopenias (without heparin treatment, neither vaccination)
Plasma from patients with HIT/HITT are usually tested diluted 1:100 with HPF4 Elisas.
This does not show the true antibody concentration.
For many well-characterized HIT/HITT patients, ELISA reactivity to HPF4 remains high when additional dilutions are tested: 1:500 to 1:20,000, demonstrating that antibody concentration can be up to 200-fold higher than estimated with the standard 1:100 dilution.
A lower reactivity to PF4 alone is noted, variable from patient to patient.
Conversely, for plasmas from patients with VITT, reactivity is higher to much higher PF4 alone, than to HPF4.
For PITT a same pattern is observed, but the HPF4/PF4 ratio, although below 1.00, tends to be higher than in VITT.
This allowed to create a reactivity index defined as the ratio of A450 to HPF4 multiplied by the dilution factor and divided by A450 to PF4 multiplied by the dilution factor.
Patients’ plasmas serial dilutions are tested until it reaches an A450 dynamic range between about 1.00 and 2.00, values then used for the index calculation.
A clear cut-off between HIT/HITT and VITT/PITT reactivities was obtained: HIT/HITT shows high to very high index values (> to >> 1.00), whilst VITT/PITT show low values < to << 1.00).
Inhibition studies by PF4 or heparin, for the antibody binding to HPF4 or to PF4, also shows differences between HIT/HITT, VITT, and PITT.”
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