Official Google Blog: Listening to Google Health users

Once he saw his data in Google Health, he saw diagnoses that were both alarming and wrong. Where did they come from?

It turns out that they came from the billing codes and associated descriptions used by the hospital to bill the patient's insurance company. These descriptions, from the International Classification of Diseases (ICD-9), often do not accurately describe a patient because the right ICD-9 code may not exist. So the doctor or hospital administrator chooses something that is "close enough" for billing purposes. In other cases, the assigned code is precisely what the doctor is trying to rule out, and if the patient turns out not to have that often scary diagnosis, it is still associated with their record. Google Health faithfully displayed the data we received on Dave's behalf. We and Beth Israel knew that this type of administrative data has its limitations but felt that patients would find it a good starting point. Too often, this is wrong.