DosiKit is a field radiation biodosimetry immunoassay for fast triage of individuals exposed to external total-body or partial-body irradiation (TBI or PBI). Assay proof-of-concept based on γ-H2AX analysis of human blood samples has been previously described as a promising tool for rapid assessment of TBI. Here, we report on the performance of the assay for PBI based on an analysis of hair follicles irradiated with a ¹³⁷Cs gamma-ray source, at doses ranging from 0 to 20 Gy and dose rates ranging from ∼0.8 to ∼3 Gy/min. First, we show that the DosiKit protocol allows extraction and analysis of hair follicle proteins. Next, we show that irradiated hair follicles trigger a DNA damage response by inducing dose-dependent γ-H2AX expression. Since γ-H2AX expression strongly decreases 2 to 4 h postirradiation, due to DNA repair, we hypothesized that an antibody targeting the S*/T*Q domains, phosphorylated by ATM for DNA repair activation (pSQTQ), would extend the postirradiation dosimetry time window. DosiKit analysis of pSQTQ in ex vivo irradiated cynomolgus monkey skin explants shows that these sequences are phosphorylated in a dose-dependent manner up to 8 h postirradiation, and that statistically different ranges of external radiation exposure can be distinguished (0–2 Gy, 5–10 Gy, 20 Gy). Since the DosiKit protocol is intended to be used on both blood and hair samples, we also show that SQTQ sequences are phosphorylated dose-dependently in human blood, allowing samples to be classified into three radiation dose ranges (0–0.1 Gy, 0.5–3 Gy and 5–8 Gy). In conclusion, radiation biodosimetry can be performed on both blood and hair samples up to 8 h after exposure using the DosiKit protocol, allowing the concomitant characterization of TBI and PBI for fast and efficient radiological crisis management.