Change Calculated Panel Reactive Antibody (CPRA) Calculation

At a glance

Current policy

Calculated Panel Reactive Antibody (CPRA) is a formula used to determine what proportion of deceased donors a potential candidate may be immunologically incompatible with and unable to accept organs from; in other words, how “sensitized” a candidate is. The more highly sensitized a candidate is, the fewer donors from which they’d be able to accept offers. The current formula is not as specific as it could be, so the OPTN Histocompatability Committee proposes updating it to better evaluate how sensitized a patient is and make sure the patient receives the most appropriate priority for allocation.

Supporting media

Presentation

View presentation

Proposed changes

• Use of National Marrow Donor Program (NMDP) data for the new CPRA formula, which includes over a hundred times more data than the OPTN data set.
• Addition of three new loci to the formula, so that candidates who are sensitized at these will receive appropriate priority.
• Addition of allele-level, or more specific, antibody values in the new formula. This allows candidates who have allele-level antibodies to receive prioritization while still being able to receive compatible donor offers typed at serologic antigen equivalents, which are less specific. Expansion of the ethnic groups utilized in approximating the deceased donor population to more accurately and inclusively represent potential donors.
• Change from a kidney-based deceased donor population to a population inclusive of all organs, to better approximate the potential donors for all waiting list candidates.

Anticipated impact

• What it's expected to do
  • Increase highly sensitized candidates’ access to transplant. Women and African American candidates will be most affected.
  • More efficiently and accurately measure a candidate’s sensitization
  • Change some candidates’ allocation priority
• What it won't do
  • Not expected to treat any candidates less favorably than the current calculation
  • Not expected to treat any particular population less favorably than the current calculation

Terms to know

• Calculated Panel Reactive Antibody (CPRA): An algorithm used to determine what proportion of deceased donors a potential candidate may be unable to accept due to immunologic incompatibility.
• Human leukocyte antigen (HLA): Proteins that differentiate between self and non-self.
• Allele: One of two or more versions of a gene, which in the context of organ transplant normally refers to the genes that create HLA proteins on the surface of a cell. Often this term is used to refer to a higher resolution typing of HLA typing, which is more specific than the serologic antigen-level HLA typing.
• Antigen: An antigen is the protein on the surface of a cell that can induce an immune response. In the context of organ transplant, an antigen normally refers to the HLA of a candidate or donor. Often this term is used to refer to “serologic antigens”, or the broader reactivity groups that the different alleles can fall into.
• Unacceptable Antigen: Alleles or antigens that a potential candidate has a high level of antibodies toward, and therefore would not be able to accept a donor with these HLA due to immunologic incompatibility.
• Loci: Locations on a chromosome where genes are found. There are 11 HLA loci primarily used in evaluation of organ compatibility. The current CPRA calculation includes 8 of these loci, and the proposed calculation includes all 11 loci.
• Sensitization: Transplant candidates are "sensitized" if their immune system makes antibodies against one or more HLA antigens or alleles in the donor pool. Sensitization usually occurs as a consequence of pregnancy, blood transfusions, or previous transplantation. Highly sensitized patients are less likely to match with available donors and more likely to reject an organ than unsensitized patients.

Click here to search the OPTN glossary