Thyroid Stimulating Hormone (TSH)
Within the medical spheres, TSH is an acronym that simply refers to the Thyroid Stimulating Hormone. It is one of the vital hormones produced by the brain’s Pituitary Gland. THS is directly responsible for stimulating and in effect controlling the levels of thyroid hormones produced by the Thyroid gland, one of the largest endocrinal glands. The location of the thyroid gland within the neck, more precisely, directly below the thyroid cartilage (which contributes to the externally visible protrusion of the Adam’s apple in men). The TSH levels chart is an important tool that is used in examining the overall health condition of the thyroid gland.
Primarily, the hormones released by the thyroid gland include, T4 (thyroxine hormone) and T3 (Tri-iodothyroxine hormone) and they essentially control the rate of metabolism within the body. They also regulate and control the functioning rate and growth of many other systems of many other systems within the body. A rather simple blood test is conducted on suspicion of irregular/abnormal thyroid activity. This test measures blood TSH levels.
The TSH chart simply showcases the normal blood TSH levels at different ages of the human body’s physical growth. The chart is comprised of two columns which include the “TSH reference range” column and Ages” column. The TSH reference range is denoted in special units of measurement referred to as the milli-International Units per liter (mIU/L). The ages of examination range from 3 days to above 14 years.
Causes of abnormal TSH levels
- TSH production is controlled by TRH (Thyrotropin – Releasing Hormone) which is secreted by the hypothalamus. The somatostatin hormone also produced by the same gland conversely, inhibits TSH production. TSH levels are affected by any imbalance between the two hormones.
- Since TSH directly controls thyroid hormone production, increased levels of TSH strongly indicates low thyroid hormone levels, a scenario which constitutes the hypothyroidism condition. Reduced thyroid hormone levels on the hand contribute to low TSH levels which in all, constitutes the hyperthyroidism.
General TSH chart
Age: 3 Days Reference Range of TSH in mIU/L: 1.10 – 17.0
Age: 10 weeks Reference Range of TSH in mIU/L: 0.60 – 10.0
Age: 14 months Reference Range of TSH in mIU/L: 0.40– 7.00
Age: 5 Years Reference Range of TSH in mIU/L: 0.40 – 0.60
Age: 14 Years Reference Range of TSH in mIU/L: 0.40 – 5.00
Age: Greater than 14 years Reference Range of TSH in mIU/L: 0.40 – 4.00
Depending on country as well as the symptoms suffered by the patient and not to mention the center of diagnosis, the THS reference range may vary. The AACE (Association of American Clinical Endocrinologists) has put forth a range of reference of 0.30 – 3.00 mIU/L while other associations suggest a range of reference of 0.40 – 5.00 mIU/L. However, it has been the general agreement that TSH levels above 2.00 mIU/L indicate a vulnerability of developing hypothyroidism. For such cases, patients are highly advised to have regular T3, T4 and TSH level check ups.
Pregnancy TSH levels
Trimester (3 month period): 1st Reference Range of TSH in Miu/L: 0.10 – 2.50
Trimester (3 month period): 2nd Reference Range of TSH in Miu/L: 0.20 – 3.00
Trimester (3 month period): 3rd Reference Range of TSH in Miu/L: 0.30 – 3.00
In the first trimester of pregnancy, an increase of the thyroidal gland activity is noted, due to the presence chorionic gonadotropin hormone (hCG). This results in T4 level increase and correspondingly a decrease in TSH levels. This happens to be necessary due to the fact that during the 1st trimester the fetus is completely dependent on the thyroid hormones of the mother.
The fetus develops its own thyroid gland within the 2nd trimester and as a result, the fetus begins producing its own thyroid hormones and as such T3 and T4 levels fall and correspondingly TSH levels rise. Due to such fluctuations. the normal range of reference for adults is not effective in diagnosing thyroidal diseases in expectant women. That’s why reference ranges specific to each trimester have been developed. The Thyroid Association of America recommends practitioners to use ranges obtained from population data provided that such a population has got an iodine intake that is optimum.
The chart above is usually recommended for those labs that have got no access to such ranges.
Unusual TSH levels
In the diagnosis of disorders of the thyroid gland, TSH levels alone are not sufficient to pass judgement. FT4 (Free T4), Total T4 (TT4) and optionally T3 levels have to be monitored as well. This in effect has got the benefit of saving time, since there will be no need for multiple separate tests for both TSH as well as T3 and T4.
FT4 levels: High, TSH Levels: Low, Diagnosis: Hyperthyroidism
FT4 levels: Normal, TSH Levels: Low, Diagnosis: Mild Hyperthyroidism
FT4 levels: Low, TSH Levels: Low, Diagnosis: Hypothyroidism (Secondary)
FT4 levels: Low, TSH Levels: High, Diagnosis: Hypothyroidism (Primary)
FT4 levels: Normal, TSH Levels: High, Diagnosis: Hypothyroidism (Mild)
The ranges of reference as defined by the National Academy of Clinical Biochemists (NACB) is as follows:
Age: 3 days Range of reference for FT4 (in picomoles/Liter): 22.0 – 49.0
Age: 10 weeks Range of reference for FT4 (in picomoles/Liter): 9.0 – 21.0
Age: 14 months Range of reference for FT4 (in picomoles/Liter): 8.0 -17.0
Age: 5 years Range of reference for FT4 (in picomoles/Liter): 9.0 – 20.0
Age: 14 years Range of reference for FT4 (in picomoles/Liter): 8.0 -17.0
Age: Greater than 14 years Range of reference for FT4 (in picomoles/Liter): 9.0 -22.0
While TSH levels chart is important in the monitoring of thyroid gland activity, it alone isn’t sufficient to diagnose thyroid disorders and as such FT4, TT4, T4 and T3 levels have to be monitored as well for a precise diagnosis.