Effects of severity of chronic obstructive pulmonary disease on thyroid function

To investigate thyroid function in chronic obstructive pulmonary disease (C OPD), 46 consecutive patients (35 men) with stable, mild-to-severe disease, having a mean (SD) age of 67 +/-7 years were studied. All subjects underwe nt pulmonary function tests (PFTs), arterial blood gas determination, and m easurement of serum total thyroxine (TT4), total triiodothyronine (TT3), re sin T3 uptake (RT3U), reverse triiodothyronine (rT3), and thyroid-stimulati ng hormone (TSH) levels. The free thyroxine and free triiodothyronine index es (FT4l = RT3U/30TT4 and FT3l = RT3U/30TT3, respectively) along with the T T3/TT4 ratio were calculated; the latter was used as a marker of peripheral conversion of thyroxine into triiodothyronine. Interleukin (IL)-6 was also measured to evaluate its potential associations with thyroidal hormone lev els. On the basis of forced expiratory volume in 1 second (FEV1), patients were divided in 2 groups: group 1, (FEV1 greater than or equal to 50% of pr edicted, n=26), with mild-to-moderate COPD and group 2 (FEV1 < 50% of predi cted, n=20) having severe disease. All subjects had normal serum thyroid ho rmone levels; for the entire COPD population, mean values were 7.80<plus/mi nus>1.60 mug/dL for TT4, 1.12 +/-0.20 ng/mL for TT3, 29.0 +/-1.88 for RT3U, 7.54 +/-1.34 for FT4l,1.07 +/-0.16for FT3l,18.71 +/-5.89 ng/dL for rT3, an d 1.15 +/-0.6 muU/mL for TSH. Mean TT3/TT4 ratio was 0.14 +/-0.03. In group 1, TT3, TT4, and TT3/TT4 ratio did not correlate with age, FEV1, PaO2, or inhaled corticosteroids. Similarly, in group 2, TT3 and TT4 were unrelated to the above-mentioned variables; however, there was a strong positive corr elation between TT3/TT4 ratio and PaO2 (r =.61, P=.004). IL-6 was within no rmal limits in all subjects, and it did not correlate with any thyroid horm one either in group 1 or in group 2. It is concluded that in stable COPD, s everity of disease through hypoxemia is important in determining the periph eral metabolism of thyroid hormones. Whether this constitutes an adaptation is not known. Copyright (C) 2001 by W.B. Saunders Company.