Most important sign in hemodynamically significant renal artery stenosis: (A) Presence of collateral vessels, (B) Elevated renin level in I/L renal vein  ≥  1.5 : 1, (C) Transstenotic pressure gradient  ≥ 40 mm Hg, (D) Decrease in renal size
Answer is A. All are signs of renal artery stenosis.
Most  important - Presence of collateral vessels.