The following 3 charts by Donor Age spell out the dynamic rank order of liver patients each time a donor comes up.
*** Remember the Wait List is very volatile ... many patients move up/down the WL based on MELD score re-certification and on/off the WL, hopefully due to getting transplanted!
The donor's hospital staff with the help of the Donate Life folks enter in the donor's vital information (age, blood type, size, etc) into UNOS' computer system to begin the matching process.
The 1st chart is for Adult Donors which I will use as my example. So if there's an 18+ age donor, UNOS looks to see if there's any suitable Status 1A (adult or peds) in the donor's Region. They will become the #1 patient for that donor. If there are (2) 1A patients, whoever has the longest wait time becomes #1 patient for that donor and the other 1A becomes #2 (back-up) patient.
If no Status1As, then UNOS looks to see if there's any suitable Status 1Bs in the donor's Region.
After that, UNOS has a toggle system between the OPO and Region for MELD 40 down to MELD 35, ranking the sickest eligible patients. Because of travel distance and liver "shelf life," it looks within the OPO first, then out to the Region for each MELD point.
After searching for eligible MELD 35+s and 1A/1Bs, then UNOS looks for the sickest MELD patient within the donor's OPO (MELD 34 down to MELD 15).
This is why your overall Regional Wait List is important and when your Region typically has low 1A/1B and 35+s, then this is why your OPO low wait list is key. 73% of livers in 2017 got allocated at the OPO level (under MELD 35).