Background: Systemic therapies targeting breast cancers associated with germline BRCA1/2 mutations (gBRCAm) have been available since 2018, approved first for locally advanced or metastatic HER-2 negative disease and more recently for use in the adjuvant setting. Prior studies have found substantial underuse of BRCA testing in breast cancer patients and disparities by socioeconomic factors. We compared rates of BRCA testing in non-elderly breast cancer patients with Medicaid vs. commercial insurance. Methods: We used the Clarivate Real-World Data Product (Clarivate RWD), a database of open claims from clearinghouses. The database links medical and pharmacy claims from ≥98% of commercial and government health insurance plans and covers 300 million lives. We identified adults ages 18-64 with commercial insurance or Medicaid with claims for breast cancer diagnosis and treatment in 2016-2021. The primary outcome was receipt of a BRCA test within 6 months after the first breast cancer (index) claim. We compared the proportion who received a BRCA test in Medicaid vs. commercial insurance. In multivariable logistic regression we estimated the impact of insurance type on receipt of a BRCA test, controlling for demographic and health characteristics. We also examined trends over time. Results: We identified 147,050 patients with commercial insurance and 41,259 with Medicaid who met inclusion criteria. The cohort was 99% female, 65% were age 50-64, 35% lived in the South, 11% had diagnosis codes for metastatic disease, and 61% had an Elixhauser comorbidity score of 0. Compared to those with commercial insurance, patients with Medicaid were younger, less likely to live in the South, more likely to have metastatic disease and have comorbid conditions. Medicaid beneficiaries were more likely to receive a BRCA test within 6 months of index claim than commercially insured patients (16.8% vs. 11.7%), with an adjusted odds ratio of 1.41 (95% CI 1.36-1.46). Receipt of a BRCA test was also more likely in patients who were male; younger; lived in the Northeast, Midwest or West; had metastatic disease or greater comorbidity. In analysis stratified by presumed stage, the advantage of Medicaid coverage was statistically significant only in patients with metastatic disease. While the proportion of all patients who received a BRCA test increased substantially in both groups beginning in 2019, it grew at a much greater rate among those with Medicaid, exceeding 20% in those patients by late 2021. Conclusions: In this analysis of health insurance claims, breast cancer patients with Medicaid were more likely to receive a BRCA test than their peers with commercial insurance, and this difference was driven by testing rates in those with presumed metastatic disease. Expanding testing in both groups could facilitate access to effective therapies for both metastatic and non-metastatic breast cancers associated with gBRCAm, thereby improving health outcomes.