The information they share includes test results and brief descriptions of conditions relevant to health or longevity. MIB rules prohibit the reporting of claims information. The MIB doesn't use the SSN as an identifier in their files, and doesn't report SSNs when providing reports. You can get a copy of your MIB file by writing to Medical Information Bureau, P.O. Box 105, Essex Station, Boston, MA 02112. Insurance is always prepaid, so they don't need to know what your credit is like, just whether your check cleared.
Some insurance companies pay interest.
You can decide whether that's worth it. Blood banks Blood banks also ask for the number but are willing to do without if pressed on the issue. They've now expunged my SSN from their database, and all the receptionists seem to know how to get by without the number. It may still be the case that some receptionists don't know about the new policy, but if you are persistent there is likely to be someone at each office who does know what to do. Blood banks have changed their policies back and forth a few times in the last several years.