Indium concentration in serum is an excellent predictor for assessing accumulated indium concentration in the lungs

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.