A method for testing for patency at a venous access site during intravenous infusion of a medical solution includes the steps of occluding an intravenous injection tube upstream from the venous access site and monitoring the time and fluid pressure within the tube while the fluid pressure within the tube is varied by external contact with the tube. An apparatus for practicing the method of the invention includes a housing formed with a tube receiving portion for holding a portion of the tube in contact with an occluder finger, a fluid moving finger and a pressure transducer. The fluid moving finger is adapted to contact the tube so as to achieve a testing base pressure in the fluid, after occlusion by the occluder finger. A sequence of pressure drops are then effected by moving the fluid moving finger in stepped increments. An excessive time interval between a pressure drop and a recovery of fluid pressure back to the testing base pressure is an indication of an infiltration condition or some other obstruction.