A customer asked why our medical record numbers are nine digits long. Their new EHR allows twelve, and they wanted to know whether they could “upgrade” their patients to longer numbers. (They can, but please don’t.)
The short answer is that the MRN is nine digits because the fax cover sheet had a box for ten characters.
The longer answer: in 2011, our first customer printed a fax cover sheet with a field labeled “MRN” that held exactly ten characters. Somebody needed one of those characters for a check digit, then somebody else decided the check digit was more trouble than it was worth and removed it, but by then nine digits was in every database, every barcode and every report. Nobody wanted to be the person who changed it.
You might think we could just pad old numbers with zeros. We tried that. It turns out that a surprising number of systems treat MRNs as integers, and an integer does not remember its leading zeros. Patient 000123456 and patient 123456 are, to those systems, the same person, which is the kind of thing that makes compliance officers develop a twitch.
It gets worse. HL7 v2 carries the MRN in PID-3, a field of type CX, which is a string. The registration system
sends 0004471902, the interface engine passes it through faithfully, and then a report somewhere opens
the CSV export in a spreadsheet, which helpfully converts it to the number 4471902 and saves it back. Now the
nightly reconciliation job compares a string to a number, decides they are different patients, and opens a
duplicate-record ticket. We have a whole queue for these. It is called the Leading Zero Queue, and it is never
empty.
Could we have used a check digit, the way credit cards use the Luhn algorithm? We did, briefly, in ZuperChart 1.0. It was a mod-11 check, which has the charming property that one in eleven numbers needs a check digit of “10,” which does not fit in one digit, so the spec said to use the letter X. The letter X then broke every system that had declared the field numeric. The check digit was removed in ZuperChart 1.1, and the release notes described this as a “performance improvement.”
So the MRN stays nine digits. It will outlive all of us.
Bonus chatter: The fax cover sheet is still in use. I checked.