Nondestructive measurements of cell persistence and gene expression are crucial for longitudinal research studies and for prognostic assessment of cell therapies. Here we describe S-MiRAGE, a platform that utilizes small secreted RNA molecules as sensitive and quantitatively accurate reporters of cellular processes. S-MiRAGE allows cellular numbers or gene expression to be measured from culture media or from biofluids. We show that multiple S-MiRAGE reporters can be multiplexed, and demonstrate the utility of S-MiRAGE by monitoring the differentiation status of human embryonic stem cells in vitro and tumor growth in a mouse model in vivo.