Searchable abstracts of presentations at key conferences in endocrinology
Endocrine Abstracts (2010) 21 P400

SFEBES2009 Poster Presentations Thyroid (45 abstracts)

Selective malabsorption of thyroid hormone or selective intake?

Rajeev Raghavan , Wolf Woltersdorf & Colin Dayan


University Hospitals Bristol NHS Trust, Bristol Royal Infirmary, Bristol, UK.


Case-1: Nineteen years old nursing student with primary hypothyroidism, despite thyroxine (T4) at 200 μg/day and subsequent trial of T4+T3, remained significantly symptomatically hypothyroid. Over 4 years worsening hypothyroidism was evident (TSH: 19.1 to >200 and fT4 2.1–6.8) despite dose/regime changes. Investigations for malabsorption: normal coeliac screen, B12, ferritin, FBC, kidney and liver function, autoimmune profile, hydrogen breath test, upper-GI endoscopy/D2-biopsy, and barium meal/follow-through, with folate and vitamin-D deficiency (20 nmol/l). Through this period, she completed her degree. Later fulltime work marred by several periods of illness requiring time off.

Assay interference with heterophile antibodies was excluded. A ‘thyroid absorption test’ (TAT) – baseline TFTs, supervised administration of oral thyroxine 200 μg, and post-dose TFTs (see Table) all repeated a week later with T4 1000 μg – demonstrated poor absorption and need for high doses to achieve adequate serum levels.

Thyroxine 600–1000 μg daily, then alternate days caused hyperthyroidism (fT4=27–95). Consequent dose reduction (any dose <500 μg) caused hypothyroidism. She is now having parenteral thyroxine 200 μg i.m. every 3 days with significantly improved quality of life and TFTs. Of note is a strong family history of hypothyroidism and maternal grandmother also being on parenteral thyroxine.

Case-2: Thirty years old Ex-army chef, primary hypothyroidism diagnosed during pregnancy 9 years prior. Gradually increasing dose of T4 to 1000 μg with suboptimal TFTs. Tests for malabsorption negative. TAT showed good absorption for both 200 and 1000 μg doses. Advised to reduce T4 to 200 μg/day.

Assay-timingCase-1: 200 μg fT4 levels1000 μgCase-2: 200 μg1000 μg
Pre-dose10.7<2.610.515.2
2-h post dose10.016.413.334.2
3-h18.540.8
4-h11.414.917.838.2
6-h11.618.440.3
24-h 9.6

Conclusions: ‘TAT’ is useful in selected cases of hypothyroidism. We have demonstrated that selective thyroxine malabsorption can occur. The exact underlying defect is currently unknown and treatment can prove challenging.

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