Decreased serum level of thioredoxin 1 in female patients with pneumonia and its combinational use with haptoglobin for the specific diagnoses of pneumonia and lung cancer

Thioredoxin 1 (Trx1) and haptoglobin (Hp) are known to be involved in pathophysiology. This study was conducted to evaluate their diagnostic significance. We employed an enzyme-linked immunosorbent assay (ELISA) to determine the concentrations of both Trx1 and Hp in sera from female patients with community-acquired pneumonia (CAP) and those with lung cancer. The Trx1 levels remarkably decreased in cases of female patients with CAP, while the Hp levels increased in both female patients with lung cancer and CAP. In addition, the serum levels of Trx1 were not significantly changed in patients with lung cancer, rheumatoid arthritis, and cardiovascular diseases compared to healthy controls. At the cut-off point of 0.396 at A_{450 nm} on the receiver operating characteristic (ROC) curve, Trx1 could discriminate between patients with CAP from normal female controls with a sensitivity of 72.5%, a specificity of 89.8%, and area under the ROC curve (AUC) of 0.877 ± 0.040. The serum levels of Trx1 in female CAP patients were inversely correlated with the levels of Hp (p < 0.05). The characteristic reduction in serum Trx1 levels, especially in female CAP patients, indicates that Trx1 could be used as a diagnostic marker for CAP. The advantage of serum Trx1 over Hp in discriminating female CAP patients among female patients who have a positive serum level of Hp suggests the use of Trx1 as an excellent combination marker with Hp for the specific diagnosis of CAP and lung carcinoma, because serum Hp levels increase in female patients with lung cancer and those with CAP without selectivity.