When there is hand tingling, how do you know if it is caused by carpal tunnel syndrome?

Location. Carpal tunnel syndrome will have tingling in the hand in the palm surface of the thumb, index, middle and 1/2 of the ring finger. It is usually not associated with pain above the elbow, but it can. Neck pain and weakness are usually signs of a pinched nerve in the neck and not carpal tunnel syndrome. A good pm&r doc or orthopedic surgeon can tell the difference easily with an examination.
EMG or MRI. It is difficult to tell if hand tingling is caused from carpel tunnel syndrome (cts) or other causes. You might try this maneuver, extend your wrist, then tap on the crease of your wrist in midline with your other index finger... Lightly. If you feel tingling in your first 3 fingers you may have cts. Confirmation of cts is usually by EMG but MRI of the wrist can demonstrate the nerve compression.