Heparin-induced thrombocytopenia during renal replacement therapy in the intensive care unit

Table 1 The 4T (thrombocytopenia, timing, thrombosis, and other causes) pretest probability of heparin-induced thrombocytopenia [6]

	Score
	2	1	0
Acute thrombocytopenia	20 to 100 × 10⁹/l, at least 30%, or any 50% fall	10 to 19 × 10⁹/l, any 30% to 50% fall, or > 50% fall post cardiac surgery	< 10 × 10⁹/l, or any < 30% fall
Timing of fall in platelet count or thrombosis or other sequalae	Clearly 5 to 10 days (or ≤ 1 day if previous heparin given for < 30 days)	5 to 10 days but not clear (or ≤ 1 day if previous heparin for 31 to 100 days), or > 10 days	≤ 4 days, with no prior heparin exposure
Thrombosis or other clinical sequalae	New thrombosis, skin necrosis, or acute systemic reaction post intravenous bolus	Progressive or recurrent thrombosis, erythematous skin lesions	None
Other cause for thrombocytopenia	No other explanation	Possible other cause evident	Definite other cause present

High total score, 6 to 8 (HIT very likely); intermediate total score, 4 to 5; and low total score 0 to 3. Timing = first day of exposure to heparin, counted as day 0.

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