Objective: Hypothyroidism is common and predominantly managed in primary care. Symptoms are non-specific, with thyroid function tests (TFT) required for diagnosis. We sought to investigate current practice in levothyroxine prescribing in primary care.
Methods: We studied the initiation of levothyroxine using the General Practice Research Database (GPRD), the worlds largest database of anonymised medical records. Individuals with i) thyroid cancer ii) secondary hypothyroidism iii) other thyroid altering medication were excluded. This was combined with a study of 444 patients (DEPTH) referred for thyroid function testing from 5 general practices and a detailed records-based analysis of the reasons for commencing levothyroxine in 104 subjects from one general practice.
Results: Fourteen thousand and nine eligible patients prescribed levothyroxine between 2000 and 2009 were identified from GPRD. The median TSH at which levothyroxine was initiated was 6.0 mU/l. 78.3% of individuals had levothyroxine initiated at a TSH level <10 mU/l and 36.2% at <5 mU/l. The odds ratio (OR) for psychological caseness amongst patients in DEPTH was 1.70 (95% CI 1.342.16, P<0.001) compared to routine general practice attenders. However, when their thyroid function was analysed there was no increased case finding for hypothyroidism OR=0.87 (95% CI 0.531.42). Detailed records analysis of 104 subjects in one general practice revealed 43.3% had levothyroxine prescribed despite being asymptomatic (median TSH 8.1 mU/l). 26.9% had levothyroxine prescribed due to classical (cold intolerance, weight gain, thin hair) symptoms (median TSH 13.1 mU/l). 29.8% were prescribed levothyroxine for other non-classical reasons (median TSH 10.1 mU/l).
Conclusion: It appears current guidelines for prescribing levothyroxine are not being adhered to, with large numbers of individuals with low mood undergoing thyroid function testing, with subsequent inappropriate initiation of levothyroxine. Individuals with depression appear to have a low probability of abnormal TFT and widespread use of TFT in individuals with depression may be unwarranted. A greater awareness of current guidelines and appropriate use of TFT is required.