This study reports two interlaboratory comparisons (ILCs) dedicated to harmonizing biological dosimetry laboratories in Spain.

Two established techniques were applied among six laboratories: the dicentric chromosome assay (DCA) and the cytokinesis-block micronucleus (CBMN) assay. In the first ILC, blood samples were irradiated ex vivo at 2.9 Gy and 1.4 Gy. In the second ILC, a 2.63 Gy exposure was delivered generating a whole-body sample and a partial-body sample.

In triage conditions using DCA, scoring 20 cells was sufficient to accurately classify doses above 2 Gy (i.e., high exposure) for rapid clinical prioritization, and 50 cells generally provided reliable estimates inside the $ \pm $0.5 Gy acceptance limit. The laboratories which could evaluate 500 cells obtained results where the 95% confidence intervals included the delivered dose. For partial-body exposures, scoring more than 50 cells was required at the tested dose (2.63 Gy) to ensure reliable DCA estimates. The CBMN assay successfully assessed whole-body exposure in the second exercise but could not identify partial-body exposure.

These ILCs demonstrate a general consistency among participant laboratories for whole-body dose assessment using both DCA and CBMN. However, further optimization is required for reliable application in partial-body triage scenarios.