The palmar surface of the fingertip (fleshy pad) of the middle (3) or ring (4) finger is usually selected for puncture for a variety of reasons. The fingertips of these fingers are usually less calloused, have fleshier pads and cause less discomfort for the patient.
The thumb (1) is to be avoided because it has a pulse. The index finger (2) tends to be more calloused, which would make collection of the specimen more difficult. This area is also more sensitive for the patient. The pinky finger (5) does not have sufficient tissue depth to prevent injury.
When performing a fingerstick, the phlebotomist should puncture either side of the fleshy pad of the middle or ring finger, but not the extreme side of the finger. The exact center of the fleshy pad or the tip of either finger should also be avoided. Avoid areas of the finger that are cold, swollen, inflamed, calloused or cyanotic. The bottom image indicates the correct area to use for skin puncture.