A novel magnetic resonance technique reveals that iron homeostasis in mesenchymal stromal cells (MSCs) strongly predicts their ability to form cartilage tissue, with balanced iron uptake and release correlating to successful chondrogenesis while excessive iron accumulation impairs differentiation capacity. The micromagnetic resonance relaxometry method tracks iron flux with sub-hour precision by monitoring culture media rather than destructively analyzing cells. This finding challenges conventional MSC quality metrics, as cell proliferation rate—despite being essential for manufacturing sufficient quantities—showed no reliable correlation with regenerative potential. The iron homeostasis marker offers particular value for cartilage repair applications, where MSC therapeutic outcomes have been disappointingly variable due to cells losing chondrogenic capacity during laboratory culture. Iron balance may serve as a universal stem cell quality indicator, as cellular iron regulation affects mitochondrial function, oxidative stress responses, and epigenetic programming—all critical for maintaining regenerative potential. The research suggests ascorbic acid supplementation preserves therapeutic quality by stabilizing iron flux rather than merely boosting proliferation. For regenerative medicine manufacturing, this could enable real-time quality assessment without sacrificing cells, potentially improving clinical outcomes across tissue engineering applications while reducing costly batch failures.