Effect of comorbidity adjustment on CMS criteria for kidney transplant center performance

Abstract

The Centers for Medicare & Medicaid Services (CMS) uses kidney transplant outcomes, unadjusted for standard comorbidity, to identify centers with sufficiently higher than expected rates of graft failure or patient death (underperforming centers) that they may be denied Medicare participation. To examine whether comorbidity adjustment would affect this determination, we identified centers that would have failed to meet 1-year graft survival criteria, 1992-2005, with and without adjustment using the Elixhauser Comorbidity Index. Adjustment was performed for each U.S. center for 24 consecutive (overlapping) 30-month intervals, including 102 176 adult deceased-donor and living-donor kidney transplant patients with Medicare as primary payer 6 months pretransplant. For each interval, we determined percent positive agreement (PPA) (number of centers underperforming both before and after adjustment, divided by number underperforming either before or after adjustment). Overall PPA was 80.8%, with no evidence of a trend over time. Among deceased-donor recipients, 10 of 31 comorbid conditions were predictors of graft failure in at least half of the intervals, as were six conditions among living-donor recipients. Lack of comorbidity adjustment may disadvantage centers willing to accept higher risk patients. Risk of jeopardizing Medicare funding may give centers incentive to deny transplantation to higher risk patients.

Figure 1

Figure 1a. Percent change in the expected number of 1-year graft failures per center, after adjustment for recipient comorbidity, 1992–2005. Figure 1b. Expected number of 1-year graft failures per center, before and after adjustment for recipient comorbidity, 1992–2005.

Figure 1

Figure 1a. Percent change in the expected number of 1-year graft failures per center, after adjustment for recipient comorbidity, 1992–2005. Figure 1b. Expected number of 1-year graft failures per center, before and after adjustment for recipient comorbidity, 1992–2005.

Figure 2

Percent positive agreement, for before and after adjustment for recipient comorbidity, for each of the 3 individual performance criteria, 1992–2005. P from a one-sided, exact Poisson test that the number of observed failures exceeds the number of expected graft failures. E, expected graft failures; O, observed graft failures.

Figure 3

Percent positive agreement, for before and after adjustment for recipient comorbidity, for each of 2 joint performance criteria, 1992–2005. Any criterion: (1) observed (O) - expected (E) events > 3; (2) ratio of O/E > 1.5; or (3) ratio of O/E significantly greater than 1, as indicated by an exact Poisson test with a one-sided P < 0.05; or all criteria (CMS rule).