Reference Article
4-18 HYPOTHYROIDISM: Screening and subclinical disease
This narrative clinical review expands on some of the recently published consensus views on hypothyroidism, in particular the role of screening and the need for treatment of subclinical hypothyroidism. I abstracted some highlights. RTJ

1. Subclinical hypothyroidism: raised thyroid stimulating hormone (TSH) level with a normal thyroxine level. The condition can be graded: Grade 1—TSH > upper limit of reference range (less than 10 mU/L); grade 2—TSH 10-20 mU/L; grade 3—over 20 mU/L. Symptoms are increasingly likely with higher TSH concentrations.
2. Clinical or overt hypothyroidism: TSH is high and the thyroxine level is low. The probability of developing overt hypothyroidism increases steadily with age, reaching 1 to 2/100 per year in women age 75-80.
   The risk of overt hypothyroidism increases in women with subclinical hypothyroidism: Relative risk (RR) = 8 for those with elevated TSH or with thyroid antibodies. RR = 38 for those with both elevated TSH and thyroid antibodies (about 5% per year.)
   "Even within the reference range of around 0.5-4.5 mU/L, a high thyroid stimulating hormone concentration (> 2 mU/L) was associated with an increased risk of future hypothyroidism. The simplest explanation is that thyroid disease is so common that many people predisposed to thyroid failure are included in a laboratory’s reference population, which raises the question whether thyroxine replacement is adequate in patients with thyroid stimulating hormone levels above 2 mU/L"
3. Screening: Screening for hypothyroidism is as favorable as screening for hypertension in the same age groups. Screening may be reasonable when focused on women over 40 visiting the doctor for non-specific symptoms.
4. Special groups: Women with diabetes are predisposed. Ideally, all diabetic women should have thyroid antibody measurements in the first trimester with careful follow-up of those with positive results. Also, any woman who develops postpartum thyroiditis should be offered annual follow-up, as a quarter of these women will develop overt hypothyroidism within the next five years.
5. Treatment of subclinical hypothyroidism: Modest symptomatic benefits may occur with thyroxine treatment in some patients with subclinical hypothyroidism. Lipid profiles may improve. Thyroxine replacement may prevent onset of overt hypothyroidism. This is particularly persuasive for people with raised TSH plus thyroid antibodies. Thyroxine requirements are less in this group than in those with overt hypothyroidism. Careful monitoring is needed.

Disadvantages of treatment: Providing the TSH concentrations are restored to the reference range there are no clinical risks. Subclinical iatrogenic hyperthyroidism must be avoided. It is associated with risk of atrial fibrillation and osteoporosis. On balance, the risks of properly monitored thyroxine treatment are almost non-existent.

CONCLUSION
Clinical and subclinical hypothyroidism are common, especially in older women.
The presence of subclinical hypothyroidism (elevated TSH) or thyroid antibodies increases the risk of developing overt hypothyroidism. The risk is greater if both are present.
Case finding in women over 40 with non-specific symptoms is the best approach to detect unsuspected hypothyroidism.
Modest symptomatic benefits may occur with thyroxine treatment in some patients with subclinical hypothyroidism. Lipid profiles may improve.
The high frequency of abnormal thyroid function tests in acutely ill patients means that testing at this time should be reserved for those in whom there is clinical suspicion of thyroid dysfunction. (See algorithm for managing subclinical hypothyroidism fig. 2 p. 1178 )
BMJ April 19, 1997; 314: 1175-78 Narrative review from Univ. Of Sheffield Clinical Sciences Centre, UK

Comment:
I believe routine TSH measurements are justifiable during clinical encounters with older patients who present with non-specific symptoms. (No need to do simultaneous T4 determinations.) The only additional cost would be the cost of the test.
A new point to me was that TSH concentration above 2 mU/L are associated with an increased risk of hypothyroidism. We should pay particular attention to patients who have TSH levels at the higher range of TSH reference levels.
There is a lot of information in the 4 page article. RTJ

[index]