Thyroid dysfunction is one of the most common clinical endocrine disorders that can lead to fatal complications such as mucinous edema coma and thyroid crisis, and is classified as hypothyroidism, subclinical hypothyroidism, hyperthyroidism and subclinical hyperthyroidism.
After reviewing the pros and cons of existing subclinical and clinical screening for thyroid disease, the U.S. Preventive Services Task Force (USPSTF) updated the 2004 USPFTF guidelines, and the new version was recently published in the Annals of Internal Medicine.
1. Overview of thyroid disorders
Hypothyroidism is defined as elevated serum thyroid stimulating hormone (TSH) with decreased thyroxine T4. Common symptoms include fatigue, coldness, weight gain, hair loss, and constipation. Subclinical hypothyroidism is usually asymptomatic and presents with elevated TSH but normal thyroxine T4; it can be divided into two categories: TSH between 4.5 and 10.0 mIU/L and TSH greater than 10.0 mIU/L.
Hyperthyroidism is defined as a decrease in TSH with an increase in T3 or T4. Symptoms are often the opposite of hypothyroidism, such as weight loss, palpitations, heat stroke, and hyperactivity. Subclinical hyperthyroidism, on the other hand, is characterized by reduced serum TSH (usually <0.4mIU/L), which can be divided into two categories: TSH in the range of 0.1-0.4mIU/L, and TSH <0.1mIU/L.
2.Introduction of the guideline
The guideline is applicable to people who are not pregnant and asymptomatic.
Risk assessment.
Risks for elevated TSH include: female, elderly, Caucasian, type 1 diabetes, Down syndrome, family history of thyroid disease, goiter, previous hyperthyroidism (in part due to thyroid dysfunction from ablative therapy), and external radiation therapy to the head and neck.
Risk of TSH reduction includes: female, old age, black race, low iodine intake, family and personal history of thyroid disease, and taking iodine-containing medications such as amiodarone.
The USPSTF believes that there is no direct evidence to confirm that treatment based on risk stratification changes final treatment outcomes. Furthermore, the optimal interval for thyroid function screening is unclear.
3. Accuracy of diagnostic methods
The sensitivity of serum TSH test is 98% and the specificity is 92%. TSH between 0.1-0.45 mIU/L does not easily progress to clinical hypothyroidism; while TSH levels ≥10.0 mIU/L easily progress to the clinical type and require consideration of starting treatment. However, it has limitations in screening for asymptomatic thyroid dysfunctional disease for the following reasons.
(1) There are no accepted guidelines for screening serum TSH levels in subclinical hypothyroidism and hyperthyroidism. Most laboratories use the upper and lower limits of the 95% reference value (0.4-4.5 mIU/L) for TSH abnormalities, with varying methods. However, the threshold is not reliable and evidence of risk of adverse outcomes is lacking.
(2) TSH secretion is influenced by ethnicity/race, gender, and age. For example, 12% of older adults (older than ≥80 years) do not have thyroid disease, but still have TSH above 4.5 mIU/L, so the threshold is not applicable to this population .
(3) TSH secretion is sensitive to other thyroid disorders. For example, TSH is often suppressed during acute onset, and is affected by the drugs dopamine, glucocorticoids, octreotide, etc. and the substance iodine. In addition, adrenal insufficiency, pregnancy, anorexia nervosa, certain autoimmune diseases, and pituitary adenomas can interfere with TSH levels.
(4) TSH levels are influenced by the cycle.
Therefore, the above points indicate that TSH alone is not sufficient to diagnose thyroid disease, but TSH testing is also necessary as a diagnostic method.
4.Treatment
The basic treatment for hypothyroidism is oral T4 monotherapy (levothyroxine sodium), while hyperthyroidism therapy includes antithyroidism (e.g., methimazole) and non-reversible ablative treatments, such as radioactive iodine with surgery.
It is generally accepted that TSH ≤ 0.1 mIU/L, especially in clinical Graves’ disease or nodular disease, requires initiation of therapy. In contrast, the conditions that usually do not require typical treatment are: TSH between 0.1 and 0.45 mIU/L or thyroiditis as the cause.
There is no evidence that subclinical hypothyroidism treatment has a beneficial effect on blood pressure, BMI, lipids, cognitive function or quality of life, but it has a long-term effect on ultimate quality of survival, reducing the risk of fracture, cardiovascular and cancer-related complications and mortality.
The USPSTF believes that false-positive results, overdiagnosis, and treatment are important disadvantages in thyroid preventive screening and need to be minimally controlled.