Objective: To clarify whether indium in serum (In-S) is an appropriate parameter for assessing accumulated indium concentration in the lungs (In-L). Methods: During our approximately 15-year Japanese cohort follow-up, five male indium-tin oxide (ITO) or/and indium trioxide-exposed workers underwent lung surgical procedures to treat lung diseases or to confirm a diagnosis of lung impairments. We measured In-L of these Cases 1-5 and were able to assess the relationship between In-L and the most recent In-S. Another 1 Japanese case (Case 6) exposed to indium trioxide and indium hydroxide was referred from an article. Results: Cases 1 and 3 had lung cancer, Case 2 suffered from recurrent pneumothorax, and Case 4 had interstitial pneumonia with mild emphysema. Case 5 had severe emphysema with pulmonary hypertension and underwent bilateral lung transplantation. In Cases 1-5, In-L and In-S ranged from 3.4 to 161.2 µg/g wet weight and 0.7 to 60.4 ng/mL, respectively, and In-L/In-S ratios ranged from 2484 to 4857. The slope of the single regression equation with zero intercept was 2767 and the correlation coefficient was 0.995. In contrast, Case 6 was extraordinarily outlying, but the reason is unclear. Conclusions: In-S is an excellent predictor for assessing indium load in the lungs in ITO or/and indium trioxide-exposed workers. However, number of cases was only five and not enough to authorize definite conclusion. It is desirable to add more cases to confirm our conclusion.
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