Factors contributing to high levothyroxine doses in primary hypothyroidism: an interventional audit of a large community database.

BACKGROUND: While few hypothyroid patients require more than the expected weight-related dose of levothyroxine, the underlying causes of larger-than-expected dosing requirements have not been studied in a single cohort. Our aim was to determine and quantify the multiple factors contributing to high-dose levothyroxine requirements in a cohort of patients with hypothyroidism. METHODS: The Grampian Automated Follow-Up Register (GAFUR) monitors around 17,500 hypothyroid patients. In 2008, 190 (1%) patients took >225 µg of levothyroxine daily. A questionnaire was sent to 174 patients (16 were untraceable) to assess causes and to offer blood tests for endomysial, parietal cell (PCA), and thyroid peroxidase (TPO) autoantibodies. Primary care practices were contacted for medication details. All patients with positive endomysial autoantibodies were referred to a gastroenterologist. Thyroid function tests and levothyroxine doses were re-evaluated in 2011. RESULTS: A total of 125 questionnaires (72%) were returned. Mean levothyroxine dose was 248 µg daily. Twenty-six patients (20.8%) took medication known to interfere with levothyroxine absorption, and 21 patients (16.8%) admitted to compliance issues. Seven patients had positive anti-endomysial antibodies on initial screening, with four being new diagnoses of celiac disease, and PCA were positive in 27 (21.6%) patients. At follow-up in 2011, the mean levothyroxine dose had decreased in patients on interfering medications and in the four new cases of celiac disease. CONCLUSIONS: Causes of patients needing high-dose levothyroxine replacement include poor compliance, medication interference, PCA (as a marker of atrophic/autoimmune gastritis), and celiac disease. Doses can be decreased following advice regarding medication or after management of underlying conditions.

Is annual surveillance of all treated hypothyroid patients necessary?

BACKGROUND: Annual surveillance (with thyroid function testing) is widely recommended for the long-term follow-up of treated hypothyroid patients. It is based largely on consensus opinion and there is limited evidence to support the frequency of monitoring. The majority of patients in our hospital based thyroid register are on 18 monthly follow-up. METHODS: We carried out a retrospective analysis to see if there is evidence to support more frequent testing. We used a logistic regression model to assess whether any baseline characteristics could be applied to predict an abnormal test. RESULTS: We identified 2,125 patients with a minimum of 10 years follow-up (89% female, 65% autoimmune hypothyroidism, and mean age at registration 51 years). There were 2 groups: 1182 (56%) had been allocated to 18 monthly follow-up and the rest had annual surveillance. The groups were well matched at baseline. Overall, during follow-up the 12 monthly group had more abnormal tests requiring dose adjustment. However, on logistic regression analysis, people aged less than 60 years, individuals taking < 150 mug thyroxine per day and people on 18 monthly follow-up had less abnormal tests. CONCLUSION: 18 monthly surveillance may be adequate in the long term follow-up of hypothyroid patients less than 60 years of age on a stable thyroxine dose of 100-150 mug/day where there are robust follow-up mechanisms in place. Implementing this strategy has potential for cost saving.