Another personal data invariant that varies
Just about anything a database might store about a person can change. People’s birthdays change (often because they’re incorrectly reported or recorded). People’s gender can change. One thing I thought didn’t change was blood type, but David Molnar pointed out to me that I’m wrong:
Donors for allogeneic stem-cell transplantation are selected based on their HLA type (tissue type), and not on their blood type. Therefore, it is quite common that the donor and patient have different blood types. The blood type is determined by the red cells. After transplant and bone-marrow recovery the red cells will come from the donor and have the donor’s blood type. As an example, if the patient is blood type A, and the donor is blood type O, the patient after transplant will become blood type O. The long-term outcome of an allogeneic stem-cell transplant is affected only to a small degree by the blood types of the donor and recipient. If an ABO difference exists, the transplant itself may create some technical difficulties, but these can be easily overcome. Red-cell recovery may be delayed after such transplants, and the patient may need support with red-cell transfusions for a prolonged period of time. More importantly, the patient should be aware that the blood type has changed or will change, and that old blood type cards are no longer valid. IBMT will provide you with a laminated card that indicates that your blood type may have changed. After your bone-marrow function has fully recovered, you may receive red cells of your new blood type. During the transplant process, usually red cells of blood type O are used, since these can be used for any patient (universal donor).
(“Indiana Blood and Marrow Transplantation“) [link to http://www.ibmtindy.com/faq/transfusions.htm no longer works]
David continues:
The Seattle Cancer Care Alliance is the #1 by volume in the U.S and does several thousand per year. So that means several people per day are having their blood type changed right here in Seattle.
Does your database and e-health record support updating your blood type record?
I actually knew this! The funny thing is, I think I learned it thanks to Law and Order. Glad to see it confirmed via a more trustworthy source.
This reminds of a Martin Fowler blog post from some time ago where he described the fact that in a health context, you don’t store “person A has blood type B”, but rather “Institution X observed on date Y that person A had blood type B”. Here‘s the associated Bliki page.