Even without the patient's name attached it is easy to identify people because of the necessary metadata in the record. If you expect to get useful information about, for instance lung disease the record will have to contain information about exposure to likely causes, age, occupation, region of the country (possibly town), sex. It will also contain marital status, whether one has children, drinking and smoking habits, weight, ethnicity.

This is pretty close to unique, just like a browser finger print.

See for instance: http://randomwalker.info/publications/no-silver-bullet-de-id...