Triphasic Dose-Response of Hematological Parameters in Healthcare Workers Exposed to Ionizing Radiations

<b>Objectives:</b> To investigate the impact of chronic and low-dose ionizing radiation (IR) exposure on the workers' hematopoietic system. <b>Methods:</b> Hematological parameters in IR exposed healthcare workers (n. 180) were compared to those determined in unexposed controls (n. 180). The relationship with the 5-year cumulative doses: <0.45; 0.45-1.28 and >1.28 mSv, was assessed. <b>Results:</b> Red blood cells (RBCs), hemoglobin (HB) and hematocrit (HCT) showed significant differences compared to controls. A non-linear relationship was determined with respect to the cumulative doses. RBCs showed a significant decrease at the first <0.45 mSv IR-dose compared to controls (4.72 ± 0.31 vs 4.90 ± 0.38 × 10¹²/L; <i>P</i> = .013) with a rising trend, although not significant, at the two highest doses. Comparably, at the two lowest doses, HB (135.8 ± 11.3, <i>P</i> < .001 and 137.4 ± 10.1 g/L, <i>P</i> < .001) and HCT (41.8 ± 2.7, <i>P</i> < .005 and 41.7 ± 2.7%, <i>P</i> < .001) significantly decreased compared to controls (143.9 ± 10.6 g/L and 43.16 ± 2.95%, respectively), while not significantly increased at the >1.28 mSv highest one. <b>Conclusions:</b> IR exposure affected the hematopoietic system according to an hormetic phenomenon, intended as a biphasic dose-response with a low-dose stimulation and a high-dose inhibition, and, potentially, through a triphasic dose-response. These results deserve attention to define/implement suitable IR occupational risk assessment and management strategies.