Heparin Induced Thrombotic Thrombocytopenia Syndrome

Dr Swapnil Pawar April 9, 2023 90

Heparin Induced Thrombotic Thrombocytopenia Syndrome
Dr Swapnil Pawar

HITT’s

Written by Dr Andrew Lam

Four T’s Score

	0	+1	+2
Thrombocytopenia	Platelet decrease <30% OR nadir <10	Platelet decrease 30-50% OR nadir 10 – 19	Platelet decrease >50% AND nadir > 20
Timing of Thrombocytopenia	Platelet Fall < 4 days without recent exposure	Unclear onset within 5-10 days, onset after day 10 OR Platelet Fall < 1 Day with prior heparin exposure within 30-100 days	Clear onset within 5-10 days OR Platelet Fall < 1 Day with prior heparin exposure within 30 days
Thrombosis	None	Progressive or recurrent thrombosis, non-necrotising skin lesions or suspected thrombosis	New thrombosis or skin necrosis Systemic Reaction post-IV Heparin
Other Causes	Definite	Possible	None appreciable

0-3 Points (Low Probability) – 1% Risk of HITT’s

4-5 Points (Intermediate Probability) – 10% Risk of HITT’s

6-8 Points (High Probability) – 50% Risk of HITT’s

Laboratory Investigations for HITT’s

Immunoassay (e.g. ELISA)

Detects the presence of PF4-Heparin antibodies
Higher incidence of false positive rates than functional assays (may detect clinically insignificant antibodies)
Results are reported as a titre level (higher the concentration of antibodies, higher risk of HITT’s

Functional Assays

Tests the ability of a PF4-heparin antibody to bind and activate platelets
More resource-intensive and require more expertise to perform and interpret
Results are reported as positive or negative

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