Geographic Disparities in Lung Transplant Rates

Martin Kosztowski; Sheng Zhou; Errol Bush; Robert S. Higgins; Dorry L. Segev; Sommer E. Gentry

Disclosures

American Journal of Transplantation. 2019;19(5):1491-1497. 

In This Article

Results

Study Population

We identified 7131 candidates who were active on the lung transplant waitlist between February 19, 2015 and March 31, 2017. Study population characteristics are shown in Table 1. This population contributed 2566 active person-years on the lung transplant waiting list. There were a total of 58 DSAs in the United States, and 42 DSAs had centers that perform lung transplants. We did not calculate transplant rates for DSAs that did not have an active lung transplant center.

Pairwise Disparity in LT Rates

After adjusting for LAS and blood type, the distribution of IRRs and MIRR is shown in Figure 1. The IRR represents a pairwise comparison of LT rate between each pair of DSAs and ranged from 1.0 to 21.73. Taking the most extreme example, an IRR of 21.73 indicates that there existed a pair of DSAs that had a 21.73 fold difference in LT rate for candidates with the same LAS and blood type, meaning a candidate moving from the DSA with a lower LT rate to the DSA with a higher LT rate would have increased their LT rate by 21.73 (Figures 2, 3).

Figure 1.

Distribution of incidence rate ratios (IRRs) and MIRR. For each pair of DSAs, the IRR is the ratio of the higher LT rate to the lower LT rates and thus IRRs were always greater than 1. MIRR was the median of all these IRRs. DSA, donation service area; IRR, incidence rate ratio; LT, lung transplant; MIRR, median incidence rate ratio [Color figure can be viewed at wileyonlinelibrary.com]

Figure 2.

Unadjusted (observed) LT rates per active person-year in the United States, by DSA. Darker colors represent higher LT rates, whereas lighter colors represent lower LT rates. Gray represents DSAs that did not have a lung transplant program during the study period. LT, lung transplant; DSA, donation service area [Color figure can be viewed at wileyonlinelibrary.com]

Figure 3.

Adjusted LT rates per active person-year in each donation service area. LT rates were adjusted for LAS and blood type. LAS, lung allocation score; LT, lung transplant [Color figure can be viewed at wileyonlinelibrary.com]

MIRR

We found significant geographic disparity in LT rates (likelihood ratio test, P < .001). The MIRR was 2.05, meaning that two candidates with the same LAS and blood type in different DSAs were expected to have a 2.05-fold difference in LT rate. Because the MIRR is interpretable as an incidence rate ratio, it is directly comparable to covariate effects—the IRRs of other factors adjusted for in our model. MIRR allows us to compare the impact of geographic location on LT rate to the impact of LAS or blood type on LT rate. An increase in LAS from 38–42 to 42–50 was associated with a 1.54-fold increase in LT rate (Table 2). This effect is less than the MIRR, so moving from LAS category 38–42 to 42–50 would have had less impact on LT rate than moving from one DSA to another. An increase from LAS category 42–50 to 50–100 was associated with a 2.43-fold increase in LT rate. This effect is greater than the MIRR, so moving from LAS category 42–50 to 50–100 would have had a greater impact on LT rate than moving from one DSA to another. By blood type, candidates with type A or AB both had a 1.25-fold greater LT rate than type O candidates. There was no statistically significant difference in LT rate for type B candidates compared to type O candidates. Blood types A and AB had higher LT rates than type O, but this effect was less than the increase in LT rate a candidate could expect from moving to another DSA.

Annual MIRR

Figure 4 shows that the MIRR calculated for each year between 2006 through 2016 ranged from 1.67 to 2.15. Simple linear regression showed that the MIRR has been increasing by 0.04 per year (slope=0.020.040.06, P < .001).

Figure 4.

MIRR was calculated for each year from 2006 through 2016. Simple linear regression showed that the MIRR has been increasing by 0.04 per year (slope=0.020.040.06, P < .001). MIRR, median incidence rate ratio [Color figure can be viewed at wileyonlinelibrary.com]

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