Geographic Patterns of Radiology Referrals in the United States: A Descriptive Network Analysis

To provide a nationwide description of radiology referral patterns for Medicare beneficiaries and network-based measures that can describe and monitor shifts in referral patterns.

We linked publicly available Medicare data with the National Plan and Provider Enumeration System data set to analyze 3,925,366 encounters representing referrals from nonradiology referrers to diagnostic radiology providers in 2015. We assessed per-state referral volume as well as in-state and in-region referrals and the correlation between state referral volume and in-state referrals. Additionally, we applied the conceptual framework of networks to create two measures to evaluate referrer-radiologist connections within each state: number of referrer relationships and referral density index (RDI).

In 2015, there was considerable variation in in-state referrals across states, and the correlation between state referral volume and in-state referrals was low (0.18). Across census regions, in-region referrals were high (84.3% in the South to 89.2% in the Midwest). Across states, the mean number of referrer relationships ranged from 7.0 in Utah to 25.0 in California, and the number of referrer relationships varied significantly within states. Radiology provider RDI also varied both within and across states, with mean radiology provider RDI spanning from 0.05 in Kansas to 0.25 in Hawaii.

In a nationwide description of geographic patterns in radiology referrals among Medicare beneficiaries, we demonstrate wide variation in radiology referral patterns and utilized network methods to develop two measures that can be used in the future to monitor shifts in referral patterns.