PF4 and deep vein thrombosis: Platelet count <150 × 109/L, D‐dimer <200 mcg/L without thrombosis, or presence of thrombosis, platelet count >150 × 109/L and D‐dimer <2000 mcg/L FEU, regardless of ELISA result for anti‐PF4 antibodies and/or alternative diagnosis more likely