Hematological changes in formaldehyde-exposed workers: A critical review and meta-analysis

Formaldehyde (FA) is a widely used chemical with known carcinogenic properties, particularly for the upper respiratory tract. Concerns about probable FA-induced hematotoxicity and leukemia have sparked investigations into its health risks. This review scrutinized the quality of exposure evaluations in studies exploring the hematotoxicity of FA and assessed the association between FA exposure and blood dyscrasias. A total of 22 studies were included in the systematic review; among them, 10 provided sufficient data for meta-analysis. FA exposure was significantly associated with changes in blood parameters, including white blood cells (standardized mean difference [SMD] = -1.450 ± 0.636), T cytotoxic cells (SMD = 2.813 ± 1.013), and natural killer (NK) cells (SMD = 1.911 ± 0.775). None of the other blood parameters were significantly affected. However, because of inconsistencies and limitations in exposure assessment methods across the reviewed studies, a clear dose-response relationship could not be established. Overall, changes in some blood parameters were possibly a response to the sensory irritation of FA in the upper respiratory tract. Based on the available scientific evidence, inhaled FA is not distributed beyond portal-of-entry to distal tissues or organs. It is recommended that the exposure of workers to FA be evaluated in a more comprehensive way by following well-validated FA sampling and analysis methods in future studies to better elucidate the association between FA exposure and hematotoxicity. Also, biological monitoring is recommended to estimate overall worker exposure to formaldehyde and to assess the association between FA exposure and its probable hematotoxicity.