Abstract
Background: Subclinical hypothyroidism (SCH) reflects the earliest stage of thyroid dysfunction with subjects having normal free thyroid hormones T3, T4 with elevated Thyroid-stimulating hormone (TSH) values. Hypothyroidism may depress the central ventilator control and affects respiratory muscle strength which is linearly related to the thyroid hormone levels. In hypothyroidism, the impairment of pulmonary functions may be initiated at the subclinical stage of hypothyroidism.

Aim and Objectives: The present study was designed to derive Forced Vital capacity (FVC), Forced expiratory volume in 1 second (FEV1), FEV1/FVC, Peak expiratory flow rate and FEF 25–75 % in subclinical hypothyroid subjects and to compare the values with that of healthy controls.

Materials and Methods: A cross-sectional comparative study was conducted in subjects aged between 25 and 60 years in which 85 subclinical hypothyroid cases were selected after proper exclusion and informed consent. 85 age and sex matched healthy controls were also studied. Statistical package for social sciences version 18 was used for statistical analysis.

Results: All spirometric variables were found to be lower in subclinical hypothyroid subjects than in healthy controls and the abnormalities were of mixed pattern-both obstructive and restrictive. All values obtained were statistically significant (P < 0.05).

Conclusion: Patients with SCH should be regularly screened with pulmonary function tests as respiratory derangement starts even at this stage. This will help for early diagnosis and treatment, and to prevent future complications.