Hypothyroidism - Diagnosis

Other Hormone Tests Used for Thyroid Function. Other hormone tests are often taken if hyperthyroidism is suspected. They include tests for triiodothyronine (T3) and thyroglobulin (also called thyroid binding globulin). Such measurements, however, may also be helpful in detecting sudden temporary increases in thyroid hormone (thyrotoxicosis) that can precede certain forms of autoimmune thyroiditis.

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Imaging Tests

Thyroid Scintigraphy. Thyroid scintigraphy tests scan the thyroid and pick up images highlighted by small amounts of radioactive substances. Thyroid scans can be used to determine whether the thyroid is producing normal amounts of hormone. The patient drinks a small amount of radioactive iodine or technetium and waits until it has been through the thyroid. Images of a properly functioning thyroid would show uniform levels of absorption throughout the gland. Overactive areas would show up white and underactive areas would appear dark. Thyroid scans are usually unnecessary unless the doctor needs to rule out suspected cancer.

Ultrasound. Ultrasound has limited value, but it can visualize the thyroid and specific abnormalities, such as nodules. (It cannot measure the thyroid gland's function, however.)

Click the icon to see an image of thyroid ultrasound.

More Advanced Imaging Tests. If laboratory tests suggest that a pituitary or hypothalamus problem is causing hypothyroidism, the doctor will usually order brain imaging procedures using computed tomography (CT) scans or magnetic resonance imaging (MRI). MRIs may also be used for determining the extent of thyroid cancers and of goiters. MRIs are also being used for investigating hypothyroidism in infants and for determining widespread effects of autoimmune thyroiditis (such as Hashimoto's hypothyroidism).

Needle Aspiration Biopsy

Needle aspiration biopsy is used to obtain thyroid cells for microscopic evaluation. It may be useful to rule out thyroid cancer in patients with suspected Hashimoto's hypothyroidism, especially if they have difficulty swallowing or develop a goiter. Much like drawing blood, the doctor injects a small needle into the thyroid gland and draws cells from the gland into a syringe. The cells are put onto a slide, stained, and examined under a microscope.

Other Blood Tests

Cholesterol levels need to be checked. Other blood tests may be performed to detect levels of calcitonin, calcium, prolactin, and thyroglobulin and to check for anemia and liver function, all of which may be affected by hypothyroidism.

Screening Recommendations for Hypothyroidism

Screening in Older Adults

Some doctors believe that because thyroid problems are so common in the elderly and thyroid hormone tests are so inexpensive, blood tests for thyroid function should be routine. Undiagnosed hypothyroidism in elderly patients can develop into a serious and even life-threatening situation. Hyperthyroidism also poses many health risks. In fact, during the period around menopause, the symptoms of menopause and hypothyroidism are similar and can easily be confused with each other.

Professional organizations differ widely on screening recommendations. Most do not recommend widespread screening for healthy adults:

The American College of Physicians recommends that women over 50 years old be screened for thyroid disorders every five years. The American Academy of FamilyPhysicians believes that adults do not have to be screened until they are over 60.
The American Thyroid Association, however, recommends that all adults, both men and women, begin their screening at age 35 and every five years afterward. Experts in this organization argue that such early screening is inexpensive and would prevent progression to hypothyroidism, and therefore possibly heart disease, in people with subclinical hypothyroidism. Such an approach would also eliminate the need for expensive anti-cholesterol drugs.

Screening in Pregnant Women

Untreated hypothyroidism in a pregnant woman, particularly in the first trimester, may have adverse neurologic effects on the unborn child. All pregnant women should be tested for thyroid function. It should be noted, however, that the elevated levels of estrogen that occur during pregnancy cause thyroid hormone levels to rise. Therefore, if a woman had low thyroid levels before pregnancy, test results for thyroxine after she gets pregnant may actually be normal. In addition, diagnosing and treating hypothyroidism even early in the pregnancy may still not prevent birth defects in the infant. Some experts go further, then, and propose that screening be done on any woman who is planning a pregnancy to help determine those who may be at increased risk for hypothyroidism and, if needed, begin treatment as early as possible during the critical first trimester.

Screening in Infants

It is very difficult to diagnose hypothyroidism in newborns by symptoms alone. Fortunately, almost all newborns with hypothyroidism are identified shortly after birth through an effective national screening program using a thyroid blood test. Each year over 1,500 children are now saved from subnormal intelligence.