The additional discriminative and reclassification value of GDF-15 beyond the independent risk factors was assessed by the category-free net reclassification improvement ( 1/2 NRI ( > 0 ) ) and the integrated discrimination improvement ( IDI ) RESULTS : Compared to GDF-15 < 1200 ng/L , a GDF-15 > 1800 ng/L was associated with an increased hazard ratio for death or spontaneous MI , mainly driven by mortality .