What is hypothyroidism?
When the thyroid gland does not secrete enough of the thyroid hormones (T4 and T3), the person’s metabolism is abnormally slow and the patient is said to have hypothryoidism.
The symtoms of hypothyroidism (below normal thyroid hormone levels) are numerous: tiredness, mild weight gain, dry skin, feeling cold all the time, yellowish skin, hoarse voice, enlargement of the the thyroid (goiter is the medical term for enlarged thyroid), abnormal knee and ankle reflexes, difficulty with coordination, constipation, slowed thinking, inability to concentrate, depression, irregular menstrual periods, abnormally heavy menstrual periods, muscle aching, abnormal blood lipids, slower than normal heart rate, swelling of the legs (myxedema). (1)
When there is severe hypothyroidism (severe deficiency of T4 and T3 and severe elevation of TSH), patients can develop anemia, a low serum sodium (called hyponatremia), and enlargement of the tongue. (3)
Very few patients will have all of the above symptoms and many will have only one or a few of the symptoms.
Patients with hypothyroidism will have abnormal blood tests; specifially an elevated TSH and a low T4.
TSH is thyroid stimulating hormone and is made in the pituitary gland located deep in the skull.
TSH regulates how much thyroid hormones (T4 and T3) the thyroid gland makes and secretes into the body.
If the the thyroid gland is unable to make enough T4 and T3, then the TSH level will rise above normal. And the T4 and T3 levels will be below normal.
Diagnosis of Hypothyroidism
So to diagnose hypothyroidism, you or your doctor (2) can order two blood tests: the TSH level and the free T4 level.
We don’t commonly order a free T3 level to diagnose hypothyroidism—rather, we use the free T3 level when we want to diagnose hyperthyroidism (too much T4 or too much T3, an overactive thyroid gland).
The normal TSH level may differ slightly from lab to lab but the normal range is around 0.4 to 5.5 microunits per milliliter. Normal T4 levels are normally between 0.8 and 1.8 nanograms per deciliter. (3)
So with hypothyroidism the TSH level will be above normal and the T4 level will be below normal.
And there are a large number of patients (from 1 to 10% of the population) who have subclinical hypothyroidism.
Diagnosis of Subclinical Hyothyroidism
“Subclinical hypothyroidism refers to mildly increased serum TSH levels in the setting of normal free T4 and T3 estimates. Although subclinical hypothyroidism may represent ‘early’ thyroid failure, it may occur in the presence or absence of symptoms.” (1)
“Treatment of subclinical hypothyroidism remains controversial, and recent arguments for and against treatment have been proposed (19,21). We believe that treatment is indicated in patients with TSH levels >10 μIU/mL or in patients with TSH levels between 5 and 10 μIU/mL in conjunction with goiter or positive anti-thyroid peroxidase antibodies (or both). These patients have the highest rates of progression to overt hypothyroidism. An initial
dosage of levothyroxine of 25 to 50 μg/day can be used, the serum TSH level should be measured in 6 to 8 weeks, and the levothyroxine dose should be adjusted as necessary.
The target TSH level should be between 0.3 and 3.0 μIU/mL. Once a stable TSH level is achieved, annual examination is appropriate.” (1)
Treatment of hypothyroidism and subclinical hypothyroidism
See upcoming blog post: How We Treat Hyothyroidism and Subclincal Hypothyroidism.
(1) AMERICAN ASSOCIATION OF CLINICAL ENDOCRINOLOGISTS MEDICAL GUIDELINES FOR CLINICAL PRACTICE FOR THE EVALUATION AND TREATMENT OF HYPERTHYROIDISM AND HYPOTHYROIDISM. 2006 amended version available at https://www.aace.com/files/hypo-hyper.pdf
(2) Order Your Own Blood Tests on the Internet. Posted Feb 21, 2012 available at https://www.tomwademd.net/2012/02/21/order-your-own-blood-tests-on-the-internet/
(3) The Cleveland Clinic Guide to Thyroid Disorders. 2009. Mario Skugor MD.