Prevalence of non‐thyroidal illness syndrome in COPD exacerbation and effect of hypoxaemia and hypercapnia on thyroid functions

Chronic obstructive pulmonary disease (COPD) is a chronic inflammatory disease showing acute exacerbations during its course. Comorbidities often accompany. Non‐thyroidal illness syndrome (NTIS) occurs because of the functional impairment in the hypothalamic‐pituitary‐thyroid axis in severe critical cases. The objective of the current study is to determine the prevalence of NTIS among hospitalised patients due to acute exacerbation of chronic obstructive pulmonary disease (AECOPD) and to reveal the factors affecting thyroid functions. Materials and methods A total of 132 patients hospitalised for AECOPD were enroled. Arterial blood gas samples at room air and venous blood samples for thyroid function tests were obtained within 24 hours following hospitalisation. Results The mean age was 69.3 ± 9.6 years with male predominance (M/F:130/2). The prevalence of NTIS was 55%. Subgroups of NTIS cases were analysed. Low TSH levels were the most common pathology (55%). Patients with NTIS had significantly lower PaO 2 and SaO 2 levels compared with those without NTIS ( P  = 0.045 and P  = 0.022, respectively). In addition, a positive correlation was found between PaO 2 and free thyroxine (fT4) ( P  < 0.001, r  = 0.313). A statistically significant negative correlation between PaCO 2 and fT4 was found ( P  < 0.001, r  = −0.393). And a statistically significant negative correlation between PaCO 2 and free triiodothyronine (fT3) values were found ( P  = 0.040, r  = −0.183). Conclusion NTIS is a very common condition during AECOPD. We believe that hypoxemia causing functional impairment in the hypothalamic‐pituitary‐thyroid axis is the main mechanism in NTIS development and hypercapnia disrupts freeT3 and freeT4 production and secretion.