PURPOSE: We investigated the association between health-related quality of life (HRQL) and the severity of hypothyroidism at diagnosis in patients referred to a secondary hospital clinic.

METHODS: Sixty-seven adult patients referred from primary care were enrolled. All patients had newly diagnosed hypothyroidism due to autoimmune thyroiditis and were treated with levothyroxine (LT4). The dose was adjusted according to thyroid function tests aiming at a normal plasma thyrotropin. Patients were stratified according to the severity of hypothyroidism in two different ways: the conventional approach (subclinical or overt hypothyroidism) and a novel approach according to the change (decrease or increase) in plasma level of free triiodothyronine index (FT3I) following LT4 treatment. The ThyPRO-39 questionnaire was used for measurement of HRQL at referral to the Endocrine Outpatient Clinic (higher score corresponds to worse HRQL).

RESULTS: Free thyroxine index (FT4I) at diagnosis correlated positively with the scores on the Hypothyroid Symptoms and Tiredness scales (p = 0.018 for both). In accordance, patients with subclinical hypothyroidism (n = 36) scored higher on Hypothyroid Symptoms (p = 0.029) than patients with overt hypothyroidism (n = 31). The difference in HRQL was more pronounced if patients were stratified according to the dynamics in FT3I following LT4 treatment. Thus, patients who showed a decrease in FT3I following treatment (n = 24) scored significantly worse for Anxiety (p = 0.032) and Emotional Susceptibility (p = 0.035) than patients with an increase in FT3I (n = 43).

CONCLUSION: Patients referred to an endocrine clinic with mild hypothyroidism had an impaired HRQL, compared to patients with more severe hypothyroidism. The most likely explanation of this finding is a lower threshold for seeking medical consultation and secondary care referral if HRQL is deteriorated. The dynamics in plasma FT3I following treatment may be more sensitive for such a discrimination in HRQL than a stratification according to the thyroid function tests at diagnosis.