To evaluate the association between cumulative radiation dose and haematological parameters among radiation workers and compare the prevalences of abnormalities in blood counts with those in the general population.

Retrospective cohort study.

Nationwide radiation dose registry in Korea, linked with occupational health examination data. Cumulative doses were estimated using annual personal dose equivalent (H_p(10)) records from 1984 onward.

The study included 20 414 radiation workers, comprising 17 651 men (86.5%) and 2763 women (13.5%), with baseline survey data, dosimetry records and at least one complete blood count (CBC) record between 2014 and 2019.

The primary outcome was the continuous haematological parameters, including white blood cell (WBC), platelet (PLT) and haemoglobin (Hb) counts, in relation to cumulative radiation dose. Associations were evaluated using linear mixed-effects models incorporating repeated measurements and adjusting for age, smoking status and body mass index. The secondary outcome was the prevalence of abnormal blood counts among radiation workers.

Most haematological parameters among radiation workers were within normal ranges. In male workers, cumulative radiation dose was associated with increased Hb levels (β=0.5 mg/dL per 1 mSv; 95% CI 0.006 to 0.9) after adjusting for age, smoking status and body mass index. No significant associations were observed between cumulative dose and WBC or PLT counts in either sex. Overall, compared with the general population, radiation workers had significantly lower standardised prevalence ratios for abnormal WBC and PLT counts.

No substantial adverse changes in haematological parameters were found among radiation workers exposed to prolonged low-dose radiation. The findings suggest that cumulative doses at occupational levels may not substantially affect CBC profiles, although continued monitoring and follow-up are warranted.