I currently work in Insurance Verfication in a local hospital... It is correct you do not need anyone's SS# but the subscriber to the insurance and most insurances make it part of the policy number... As to why they ask, there may be a couple of reasons... First, most medical software systems now ask for the SS# as away to locate the patient... Second, we run into patients who may have been a patient when they were younger who come back married... if we do not have their SS#, we may end up assigning them a new medical record number, thus not having any of their past history available... Finally, we are society of numbers now... It is easier to locate a patient by their SS# then to question, all the other information and depending on their patient to remember the last time they were there and if their name is the same (happens often)... Having said all that, it is up to you if you feel comfortable or not giving out the information... I can state that in the my work, we do not use anyone but the subscriber's number.
HIPAA is a governing act that protects patients' privacy.