What Could Cause Painful Blister?

my friends' father had blisters having a size of a pinky finger (from tip to first crease line) and her father is complaining of pain on that area. he also complained of pain coming from the back radiating to the chest. the result of his sgpt result is 80. what could be the interpretation for this condition? is the blister related to a possible formation of herpes zoster? thank you.