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Standard practice to minimize variability in beta cell function (BCF) measurement is to test in inpatient (IP) settings. IP testing strains trial subjects, investigators, and budgets. Outpatient (OP) testing may be a solution although there are few reports on OP BCF testing variability. We compared variability metrics between OP and IP from a standardized mixed meal tolerance test (MMTT) and arginine stimulation test (AST) in two separate type 2 diabetes (T2DM) cohorts (OP, n = 20; IP n = 22) in test-retest design. MMTT variables included: insulin sensitivity (Si); beta cell responsivity (Φtot); and disposition index (DItot = Si* Φtot) following 470 kCal meal. AST variables included: acute insulin response to arginine (AIRarg) and during hyperglycemia (AIRargMAX). Results Baseline characteristics were well-matched. Between and within subject variance for each parameter across cohorts, and intraclass correlation coefficients (ICC-a measure of reproducibility) across parameters were generally comparable for OP to IP. Table summarizes the ICC results for each key parameter and cohort. Test/Parameter Outpatient (95% CI) Inpatient (95% CI) MMTT: Si 0.49(0,0.69) 0.28(0,0.60) MMTT: Φtot 0.65(0.16,0.89) 0.81(0.44,0.93) MMTT: DI 0.67(0,0.83) 0.36(0,0.69) AST: AIR Arg 0.96(0.88,0.98) 0.84(0.59,0.94) AST: AIR Arg Max 0.97(0.90,0.99) 0.95(0.86,0.97) AST: ISR 0.93(0.77,0.97) 0.93(0.82,0.96) In conclusion, the variability (reproducibility) of BCF measures from standardized MMTT and AST is comparable between OP and IP settings. These observations have significant implications for complexity and cost of metabolic studies.