Association Between Specialist Distribution and Regional Variation in Plasmapheresis Use in Japan: A Population-Level Cross-Sectional Study.

Plasmapheresis is widely used in Japan; however, regional variation in its use and its association with specialist distribution remain unclear. We conducted a cross-sectional study using the 9th National Database Open Data (fiscal year 2022) to assess regional variation in plasmapheresis use and examined its association with the distribution of nephrologists, dialysis specialists, and apheresis specialists. Plasmapheresis use was identified using the relevant receipt code, and age- and sex-adjusted standardized claim ratios (SCRs) were calculated. Plasmapheresis use differed 6.5-fold across regions, with SCRs ranging from 34.0 to 222.4. Multivariable-adjusted negative binomial regression models showed that each additional board-certified nephrologist per 100 000 population was associated with a 1.11-fold increase in the SCR (β = 0.11; 95% confidence interval: 0.02-0.20; p = 0.022). No significant associations were observed for board-certified dialysis or apheresis specialists. These findings indicate substantial regional disparities and suggest that nephrologist distribution may influence plasmapheresis utilization in Japan.