Abstract: Early diagnosis of lethal radiation is imperative, since the intervention time windows for lethally irradiated subjects are considerably short. Hence, ideal diagnostic candidates of radiation should be easily accessible, enable to inform the stress history and triage subjects unbiasedly in a time-efficient manner. Taken together, small molecules such as metabolites and microRNAs (miRNAs) from plasma are legitimate biomarker candidate for lethal radiation. Herein is described a TBI (total body irradiation) model involving minipigs exposed to radiation. Markers were observed at early, intermediate and late time periods post-radiation, and were compared to non-exposed, non-radiated miRNA's. A method and a kit for detecting time-dependent ionizing radiation exposure is described in embodiments herein.