High free T4 causes

There are 2 thyroid hormones as T4 and T3  produced by thyroid gland. Pituitary gland secretes TSH ( thyroid stimulating hormone) and TSH stimulates thyroid gland for thyroid hormone T4 and T3 production.

free t4

Thyroid gland is a small, butterfly shaped gland in front of your neck, below the Adam’s apple. Thyroid  gland produces T4-thyroxine and T3-triiodothyronine thyroid hormones to balance body metabolism. Thyroid hormones regulates metabolism and have so many important functions ;

Thyroid hormone functions in your body


  • Metabolic rate
  • Heart rate
  • Carbohydrate metabolism
  • Weight gain
  • Weight loss
  • Body temperature
  • Cholesterol level
  • Brain development
  • Baby growth
  • Menstruation
  • Nervous system functions


There are 2 forms of T4 in your body.  99% of the T4 is bonded to thyroid hormone-binding proteins like albumin or globulin and the rest part is free T4. Free T4 is the suitable form for body usage, other part of T4 is transformed to T3  for body activities. T3 is the more active thyroid hormone in body.

free t4

High T4 causes

T4- thyroid hormone level may be found high because of several reasons but only T4 increasing may not be enough for diagnosis. Additionally T3 and TSH thyroid hormone levels are important for hypothyroidism or hyperthyroidism diagnosis.  T4 hormone level may be found increased by some causes like;

  • Pregnancy
  • High blood protein level
  • Too much iodine intake
  • Subacute thyroiditis
  • Postpartum thyroiditis
  • Graves disease
  • Primerhyperthyroidism
  • Toxic thyroid adenoma
  • High dose thyroid treatment medication
  • Germ cell tumor
  • Struma ovarii – ovarian tumor
  • Plummer disease- toxic multinodular goitre
  • Molar pregnancy
  • X-ray dyes that include iodine


Free T4 normal levels


  • Adult: 0.58-1.64 ng/dL
  • Pregnants first trimester: 0.73-1.13 ng/dL
  • Pregnants second trimester: 0.54-1.18 ng/dL
  • Pregnants third trimester: 0.56-1.09 ng/dL


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