& 2 points if the fall in platelet count is >50\% of the previous value, AND the lowest count (nadir) is 20 100 × 109/liter\newline
1 point if the fall is 30–50\% or the nadir is 10–19 × 109/liter\newline
No points if the fall is less than 30\% or the nadir is <10 × 109/liter. \\\hline
Timing & 2 points if the fall is between days 5–10 after commencement of treatment\newline
1 point if the fall is after day 10. If someone has been exposed to heparin within the last 30 days and then has a drop in platelet count within a day of reexposure, 2 points are given. If the previous exposure was 30–100 days ago, 1 point\newline
If the fall is early but there has been no previous heparin exposure, no points. \\\hline
Thrombosis & 2 points in new proven thrombosis, skin necrosis (see below), or systemic reaction\newline
1 point if progressive or recurrent thrombosis, silent thrombosis or red skin lesions\newline
No points if there are no symptoms. \\\hline
Alternative cause possible & 2 points if no other cause\newline
1 point if there is a possible alternative causeNo points if there is a definite alternative cause. \\
