How this calculator works
This page implements the standard 4Ts table reproduced by Cuker and colleagues in 2012, using the days 5 to 10 timing definition. The platelet domain combines the fall and nadir: a fall below 30% or nadir below 10 gives zero; a fall above 50% with nadir at least 20 gives two; the remaining combinations give one. Add timing, thrombotic features and alternative causes for a total from zero to eight. Missing clinical information requires reassessment, not a guessed answer. A category is not a confirmed HIT diagnosis. The result is an estimate for information only and is not medical advice.
Formula
4Ts = platelet-domain points + timing points + thrombosis points + other-cause points. Low: 0 to 3; intermediate: 4 to 5; high: 6 to 8.
Worked example
A 60% platelet fall to 30 x 10^9/L, clear day-7 onset, confirmed new thrombosis and no other cause gives 2 + 2 + 2 + 2 = 8. A 40% fall to 15, uncertain timing, no thrombosis and a possible other cause gives 1 + 1 + 0 + 1 = 3.
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Frequently asked questions
Does a high score confirm HIT?
No. The 4Ts estimates pretest probability and must be combined with appropriate clinical and laboratory assessment.
Does a fall of exactly 50% score two?
No. The two-point fall criterion is strictly above 50%, with a nadir of at least 20 x 10^9/L.
Can I reconstruct the clinical inputs from a total score?
No. Many different clinical combinations have the same total, so this tool scores forwards only.