Medicare Coverage of Routine Screening for Thyroid Dysfunction (2003) / Chapter Skim
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3. Prevalence and Consequences of Thyroid Dysfunction
3. Prevalence and Consequences of Thyroid Dysfunction
Pages 21-31
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From page 21... ...
Persons with "subclinical" hyperthyroidism or hypothyroidism may display clear symptoms or signs of thyroid dysfunction while those with "overt" hyperthyroidism or hypothyroidism may show no other evidence of thyroid dysfunction. In all population surveys, most of the abnormal serum TSH concentrations are just outside the normal range, indicative of very mild thyroid dysfunction, and the frequency of more abnormal values is considerably lower.
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From page 22... ...
Among people who are found by screening to have abnormal serum TSH concentrations, careful evaluation will often reveal symptoms or signs of thyroid dysfunction, as described in the preceding chapter. In general, those people whose screening tests indicate subclinical thyroid dysfunction more often have none or fewer of these symptoms and signs than do those people whose screening tests indicate overt thyroid dysfunction.
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From page 23... ...
In the overall population of persons with thyroid dysfunction defined by abnormal serum TSH concentrations, those who also have abnormal serum T4 will be much more likely to have clinically recognizable morbidity and potential to benefit from treatment. The screening population, however, is a much more homogeneous group; subjects, by definition, lack recognized morbidity.
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From page 24... ...
CONSEQUENCES OF SUBCLINICAL HYPOTHYROIDISM The consequences of subclinical hypothyroidism are symptoms attributed to thyroid deficiency, the presence of biochemical or physiological abnormalities that might be a threat to the person's health and quality of life, and the risk of progression to more severe thyroid dysfunction. In the screening population, the consequences of biochemically overt hypothyroidism are similar, but presumably greater.
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From page 25... ...
that affect serum cholesterol values, perhaps more relevant is the extent to which serum cholesterol values change with thyroid hormone treatment in patients with subclinical hypothyroidism. A systematic review of the effect of thyroid hormone therapy in these patients revealed a mean decrease in serum cholesterol concentration of 7.9 mg/dl (0.2 mmol/L)
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From page 26... ...
who had subclinical hypothyroidism were followed for a prolonged period (20 years) , the average rate of progression to a clinical diagnosis of hypothyroidism in women was 3 percent per year in those with high serum TSH concentrations and 4 percent per year in those with high serum TSH concentrations and high serum antithyroid peroxidase antibody concentrations (Vanderpump et al., 1995~.
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From page 27... ...
Based on extrapolation from a figure in the article, the prevalence of low serum TSH concentrations was 1 percent in people aged 60 to 69 years and 70 to 79 years, and 3 percent in those aged 80 years and older. In the Colorado Thyroid Disease Prevalence Study, 219 of 24,337 people (0.9 percent)
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From page 28... ...
, and the percentage of people who had normal serum TSH concentrations when retested varied, ranging from 14 percent to 61 percent (summarized in Marqusee et al., 1998~. These wide variations undoubtedly reflect differences in the cause of the subclinical hyperthyroidism, and indeed the likelihood that in some people, the low serum TSH concentration was caused by transient nonthyroidal illness.
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From page 29... ...
Some people have biochemical or physiological abnormalities that are ameliorated by thyroid hormone therapy, in the case of people with subclinical hypothyroidism, or antithyroid therapy, in the case of subclinical hyperthyroidism. Among people with thyroid dysfunction, therapy may have beneficial effects on intermediate outcomes, such as reduction in serum lipid concentrations and improvement of myocardial contractility.
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From page 30... ...
, and thyroid antibodies in the United States population (1988 to 1994) : National Health and Nutrition Examination Survey (NHANES III)
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From page 31... ...
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