Hypothyroidism is due to decreased or absent production of thyroid hormone.
Primary hypothyroidism is caused by generalized tissue resistance to thyroid hormone and disorders that affect the thyroid gland directly. It is responsible for majority of hypothyroid cases.
Central hypothyroidism is caused by hypothalamic or pituitary disorders.


Differentiating between primary, central & subclinical hypothyroidism

  • Primary hypothyroidism: Low free thyroxine (FT4) & elevated serum thyroid-stimulating hormone (TSH)
  • Central hypothyroidism: Low FT4 & low, normal or mildly elevated serum TSH
  • Subclinical hypothyroidism: Elevated TSH & normal FT4
    • Repeat thyroid function test should be done after 3-6 months to confirm the diagnosis

Additional thyroid tests may include the following

  • Thyroid autoantibodies: Antithyroid peroxidase & antithyroglobulin autoantibodies
  • Thyroid scan, ultrasound
  • Fine needle aspiration (FNA): Recommended for all palpable solitary or dominant nodules, independent of size
    • FNA is preferred over thyroid scan or ultrasonography as the initial diagnostic test for thyroid nodules, although a previous ultrasound may aid the physician in performing the aspiration


  • Prolonged gestation
  • Maternal history of thyroiditis (transient neonatal hypothyroidism)
  • Maternal exposure to radioiodine or intake of goitrogens (eg Amiodarone, antithyroid drugs)
  • Family history of hypothyroidism
  • Thyroid treatment for hyperthyroidism (eg Thionamides, radioiodine or surgery)
  • Viral infection followed by a painful thyroid gland w/ signs & symptoms of hyperthyroidism, later on manifesting signs & symptoms of hypothyroidism (subacute thyroiditis)
  • Iodine sources (Iodine deficiency/endemic goiter)
  • Excessive iodide intake (eg Kelps, radiocontrast dyes)
  • Intake of goitrogens (eg Lithium, Amiodarone, thionamides)
  • Head & neck radiation

Laboratory Tests

  • Patient’s age must be considered in the interpretation of thyroid function results

Confirmation of Hypothyroidism

  • Serum thyroid-stimulating hormone (TSH): Most valuable test for detecting hypothyroidism
  • Free thyroxine (FT4) levels also useful for confirmation
  • TSH & FT4 concentrations are higher in children, especially in the 1st week of life & throughout the 1st year


Acquired Hypothyroidism

  • If suspected, the entire function of the hypothalamic-pituitary axis should be evaluated w/ appropriate tests
    • Once confirmed imaging studies of the brain & pituitary gland should be performed

Congenital Hypothyroidism

  • Most infants appear unaffected at birth; signs & symptoms may be delayed until 6-12 weeks of age or older
  • Newborn screening for congenital hyperthyroidism is crucial for early detection & treatment
    • Delaying treatment after 6 weeks of life is associated w/ increased risk of delayed cognitive development
    • Abnormal laboratory results must be communicated immediately so that empirical thyroid hormone replacement can be initiated even while waiting for confirmatory studies


  • Present or absent femoral/tibial epiphyses in radiographic imaging of the knee may help assess the severity of intrauterine hypothyroidism
  • Scintigraphy & ultrasonography may also be used to assess the patient’s thyroid function & cause of the disease
    • Performing both scintigraphy & ultrasound is highly suggested in neonates w/ high thyroid-stimulating hormone (TSH) levels


Newborn Screening for Congenital Hypothyroidism

  • Goals of screening: To identify & treat patients at risk for the health consequences of thyroid dysfunction before they become clinically apparent
  • Additional indications & ideal time for screening:
    • Normal hospital delivery at term: 2-4 days of age
    • Infants in neonatal intensive care units (NICU), preterm babies, home births: Within 7 days of age
    • Maternal history of thyroid medication or family history of congenital hypothyroidism: Cord blood for screening

Types of newborn screening:

  • Primary thyroid-stimulating hormone (TSH), backup free thyroxine (FT4): May miss thyroid-binding globulin deficiency, central hypothyroidism, hypothyroxinemia w/ delayed TSH elevation
  • Primary T4, backup TSH: May miss delayed TSH elevation w/ initial normal T4
  • Primary T4 & TSH: Ideal screening approach

Interpretation of newborn screening results:

  • Elevated TSH & low T4: Congenital hypothyroidism
  • Normal TSH & low T4: Transient hypothyroxinemia, central hypothyroidism, thyroid-binding globulin deficiency, isolated low T4
  • Elevated TSH & low T4: Transient/permanent mild congenital hypothyroidism, delayed maturation of hypothalamic/pituitary axis, thyroid hormone resistance, Down syndrome
  • Delayed TSH elevation & low T4: Low or very low-birth wt infants, preterm infants, sick term newborn

Confirmation of results

  • Infants w/ abnormal or borderline screening results should have free T4 & TSH drawn for definitive testing
    • Thyroid hormone replacement may be empirically initiated while awaiting confirmatory results

Secondary Screening for Congenital Hypothyroidism

Recommended for the following:

  • Preterm neonates
  • Infants w/ low-birth weight (LBW)
  • Infants w/ very low-birth weight (VLBW)
  • Unhealthy infants/preterm neonates previously admitted in the NICU
  • Newborn screening done w/in 1st 24 hours after birth
  • Multiple pregnancy
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