If you're waiting for a kidney transplant, you may have heard terms like cPRA, cRF, or vPRA. These numbers estimate how difficult it will be to find a compatible donor for you. This guide explains what they mean and why they matter.
The problem: your immune system has a memory
Your body can distinguish "self" from "foreign" using proteins called HLA (Human Leukocyte Antigens). These proteins sit on the surface of your cells like name badges, identifying them as yours.
When you encounter foreign HLA — through a previous transplant, pregnancy, or blood transfusion — your immune system may create antibodies against those specific HLA types. These antibodies remember what they've seen.
If a donor has HLA types that match antibodies you've developed, your body would attack the transplanted organ immediately. This is called a positive crossmatch, and it means that donor isn't suitable for you.
People who have developed these antibodies are called "sensitised". The more antibodies you have, and the more common the HLA types they target, the fewer donors will be compatible with you.
The metric: one number that summarises your situation
cPRA and its equivalents answer a simple question:
Out of 100 random donors, how many would be
incompatible?
A higher number means a longer wait and fewer organ offers. Someone with a cPRA of 99% might wait years for a compatible donor to become available.
Different names, same concept
Different countries use different names for essentially the same metric:
| Region | Name | Stands for |
|---|---|---|
| USA + rest of the world | cPRA | Calculated Panel Reactive Antibody |
| UK | cRF | Calculated Reaction Frequency |
| Eurotransplant | vPRA | Virtual Panel Reactive Antibody |
Think of it like "petrol" versus "gas" — different words for the same thing.
Why does this number matter?
Your cPRA/cRF affects your transplant journey in several ways:
- Allocation priority: Highly sensitised patients often receive extra priority points, recognising that compatible organs are rare for them.
- Offer decisions: When an organ becomes available, your transplant team uses this number to quickly assess whether it's worth pursuing.
- Special programmes: Some treatments are only available to patients above certain thresholds. In the UK, for example, the desensitisation drug imlifidase is only offered to patients with cRF of 99% or higher.
The bottom line
cPRA, cRF, and vPRA are different names for a metric that estimates how hard it is to find you a compatible donor. A higher number means fewer compatible donors exist, which typically means a longer wait.
If you'd like to know your cRF/cPRA/vPRA score, ask your transplant team — they can explain what it means for your situation.