In subclinical hypothyroidism, TSH concentrations are above the reference range and FT4 concentrations are normal. Make the diagnosis only after a confirmatory result on repeat testing within three to six months.
What should you do next?
Review to check for a goitre or clinical signs of hypothyroidism. Repeat the TSH level and FT4 within three to six months, and check serum thyroid peroxidase antibodies (TPO-Ab).
Should you treat?
- Consider offering levothyroxine treatment if there is a goitre or the patient's TSH level is rising.
- Consider a trial of levothyroxine only if there are symptoms compatible with hypothyroidism. Only continue treatment if there a clear improvement in symptoms is seen.
- If no treatment is necessary, monitor:
- If she is TPO-Ab positive, measure serum TSH annually or earlier than this if symptoms develop.
- If she is TPO-Ab negative, measure serum TSH approximately every three years, or earlier if symptoms develop.
CKS have based these recommendations on a consensus guideline produced by the Association for Clinical Biochemistry, the British Thyroid Association, and the British Thyroid Foundation.1 They are based on evidence from well- conducted non-randomised clinical trials and expert opinion.
Several prospective studies on different populations have shown that only a small percentage of patients with subclinical hypothyroidism will become overtly hypothyroid each year.2,3
A number of studies found that the likelihood of improvement with treatment is small, and there is some concern about inadvertent overtreatment with levothyroxine (for example, possible effects on bone mass and potential cardiac complications).4
However, CKS recognise that some patients with TSH levels between 4.5 and 10mU/l have symptoms compatible with hypothyroidism,5 therefore the clinician should use clinical judgment and discuss with the patient to decide whether a trial of levothyroxine is worthwhile (while monitoring for an improvement in symptoms).
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Reliable, evidence-based answers to real-life clinical questions, from the NHS Clinical Knowledge Summaries in association with GP. See www.cks.nhs.uk
1. BTA, ACB and BTF (2006) UK guidelines for the use of thyroid function tests. Association for Clinical Biochemistry, British Thyroid Association, British Thyroid Foundation. www.acb.org.uk (Accessed: 07/10/2008).
2. Vanderpump MPJ, Tunbridge WMG, French JM et al. The incidence of thyroid disorders in the community: a twenty-year follow-up of the Whickham Survey. Clinical Endocrinology 1995; 43(1): 55-68.
3. Vanderpump M. Subclinical hypothyroidism: the case against treatment. Trends in Endocrinology and Metabolism 2003; 14(6): 262-6.
4. Cooper DS. Subclinical hypothyroidism. N Engl J Med 2001; 345(4): 260-5.
5. Surks MI, Ortiz E, Daniels GH et al. Subclinical thyroid disease: scientific review and guidelines for diagnosis and management. JAMA 2004; 291(2): 228-38.