Estimated Post-Transplant Survival (EPTS) Score

Variables considered

The estimated post-transplant survival (EPTS) score is based on the following variables:

■ Patient age;

■ Current diabetes status: (none type I, type II, other type);

■ Previous solid organ transplants: (none, one or more);

■ Regularly administered dialysis for ESRD;

■ In case dialysis variable is positive, the following two fields appear:

- Initiation date of dialysis for ESRD;

- Calculate EPTS as of a specific date;

Currently, the methodology says that the diabetes status and the number of prior transplants need to be disclosed by the candidates for kidney transplant.

EPTS score formula

The Organ Procurement and Transplantation Network (OPTN) policy uses the following formula for calculating the EPTS:

Raw EPTS = 0.047 x max (Age – 25, 0) + (-0.015) x Diabetes x max (Age – 25, 0)

+ 0.398 x Prior solid organ transplants + (-0.237) x Diabetes x Prior solid organ transplants

+ 0.315 x log(Years on dialysis + 1) + (-0.099) x Diabetes x log(Years on dialysis + 1)

+ 0.130 x (Years on dialysis = 0) + (-0.348) x Diabetes x (Years on dialysis = 0) + 1.262 x Diabetes

The following explains how the transplant candidate characteristics are accounted for in the formula:

■ Age – measured in fractional years as the number of full days between current date and candidate date of birth divided by 365.25.

■ Diabetes – binary factor, 0 if no diabetes diagnosis present and 1 if any type of diabetes is present.

■ Prior organ transplant – binary factor, 0 if no prior transplants and 1 if one or more transplants.

■ Years on dialysis – measured in fractional years, which is the difference between current date or date selected by user and dialysis start date, divided by 365.25.

■ If the patient is not under dialysis, then Years on dialysis becomes 0 and “Years on dialysis = 0” is treated as 1.0 in the formula.

The Raw EPTS is then converted to the cumulative percentage based on the official EPTS Mapping Table.

The original study has determined the formula through a multivariable Cox proportional hazards regression model.

Interpretation

EPTS scores range between 0% to 100%. The lower the score, the higher the benefit the patient is expected to have from receiving the graft function, compared to candidates that have higher scores.

According to the above rule, EPTS is used to create two groups of patients, one with candidates with scores of 20% or below and one with candidates with scores above 20%.

Therefore, the rule indicates that candidates with scores of 20% and below are matched first with donors and the first targeted donors also have to have KDPI scores of 20% or less.

In each group, the CPRA or the HLA-DR matching are used, amongst other determinants, to establish waiting time.

The system also updates the scores to account for changes in lapsed time and changes in patient status.

References

1. A Guide to Calculating and Interpreting the Estimated Post-Transplant Survival (EPTS) Score Used in the Kidney Allocation System (KAS). (2014) Organ Procurement And Transplantation Network.

2. Clayton PA, McDonald SP, Snyder JJ, Salkowski N, Chadban SJ. External validation of the estimated posttransplant survival score for allocation of deceased donor kidneys in the United States. Am J Transplant. 2014; 14(8):1922-6.