Differences in thyroid hormone prescribing practices between Japan Thyroid Association-certified thyroid specialists and non-certified members: a nationwide survey in Japan.

Thyroid hormone (TH) prescribing practices, particularly on hypothyroid and euthyroid patients, were compared between Japan Thyroid Association (JTA)-certified thyroid specialists and non-certified members. A nationwide questionnaire survey (Treatment of Hypothyroidism in Europe by Specialists: An International Survey) was conducted among all 2,938 JTA members, including 874 certified specialists and 2,064 non-certified members, to assess self-reported TH prescription choices in various clinical scenarios. Responses from certified specialists and non-certified members were statistically compared. A total of 207 certified specialists (23.7%) and 129 non-certified members (6.3%) responded and completed the questionnaire. Although all certified specialists and non-certified members selected levothyroxine (LT4) as first-line therapy for hypothyroidism, certified specialists more often used liothyronine (LT3) plus LT4 combination therapy than non-certified members (28% vs. 12%, p < 0.001), particularly for LT4-treated patients with persistent hypothyroid-like symptoms (9% vs. 2%, p = 0.02). For euthyroid individuals, 71% of certified specialists and 60% of non-certified members considered TH treatment (p = 0.043). Non-certified members who see >100 hypothyroid patients per year were more inclined to use combination therapy for hypothyroid patients and TH for euthyroid patients than those of ≤100 patients (p < 0.049 and 0.001, respectively). In conclusion, JTA-certified thyroid specialists and non-certified members exhibit distinct TH prescribing patterns. Certified specialists are more open to combination therapy and treating selected euthyroid patients, whereas non-certified members favor guideline-based LT4 monotherapy. These differences underscore the impact of specialization on clinical practice and suggest a need for updated guidelines and targeted education to rationalize thyroid care.