Endocrine Abstracts

Background: In clinical practice, occasional hypothyroid patients require more than the expected dose of levothyroxine. This could be due to compliance issues, excess body weight, drug interference or malabsorption. The Grampian Automated Follow-Up Register (GAFUR) currently monitors around 17 500 hypothyroid patients on levothyroxine; 36 (0.6%) patients take more than 250 μg of levothyroxine daily.

Methods: A questionnaire was sent to these patients to assess causes for increased T4 requirement and they were offered a blood test for IgA anti-endomysial antibody (immunofluorescent method), which has 97% sensitivity and 98% specificity for the detection of coeliac disease. GP surgeries were contacted for medication details and other medical conditions.

Results: Twenty-four questionnaires (67%) were returned. Mean age was 50 years with 58% females. Mean BMI was 34.7 (range 21.7–53.9). Mean levothyroxine dose was 300 μg and in all patients the dose was well above the expected weight-related dose. Mean TSH level was 6.0 mU/l (range: <0.10–28) and mean fT4 levels was 15.2 pmol/l (range: 9.0–23.0). Only 6 patients (25%) admitted to having compliance issues (at least one missed dose per week). There were 7 (29%) patients who were on additional medications which could interfere with levothyroxine absorption (PPI, anticonvulsants, calcium salts & ferrous sulphate). Six patients (25%) had gastrointestinal symptoms of abdominal bloating and diarrhoea; one patient not known to have coeliac disease was found to have a positive anti-endomysial antibody test. Two patients were previously known to have pernicious anemia.

Conclusions: High doses of levothyroxine needed in a minority of hypothyroid patients are due to multiple factors. Apart from compliance issues, interfering medications are under-recognised. Autoimmune gastritis and coeliac disease are established causes of malabsorption and should be sought in these patients.