Diagnosis of Hypothyroidism

Proper diagnosis of hypothyroidism (indeed all thyroid disease), involves the consideration of data derived from:

  1. Laboratory testing
  2. Thorough evaluation of the patient’s symptoms during medical history intake
  3. Physical examination to determine any potential signs related to thyroid imbalance

Important note on laboratory testing: while lab results should be taken into account, sole dependence on lab results in unadvisable due to a lack of universal consensus on ”normal” ranges for thyroid hormone levels. Traditionally, in the absence of any other underlying cause(s) explaining the patient’s symptoms (i.e.; low energy, depression and weight gain, etc.), an erroneous diagnosis or lack of diagnosis might result. I see this approach as diagnosing and treating lab results but not the patient.

Limitations of blood tests as a sole method of diagnosis of low thyroid function:

  • Thyroid blood concentration varies throughout the day, so the lab test is a snapshot of what is going on in the blood at one moment in time
  • Thyroid blood levels can be affected by prescription drugs, imbalances in other hormones in the body, as well as disease processes
  • The “normal” laboratory range of thyroid hormones is an arbitrary number. It simply reflects the “normal” range for 90-95% of the population.
  • The arbitrarily defined normal value has actually changed over time, for instance the normal laboratory range for the free thyroxin was lowered 15 percent from 1991-2001.
  • Effect of aging on thyroid gland function: with age the ability of our thyroid to make hormones declines.
  • Blood values do not represent the production of active hormone or T3 inside the cells outside the thyroid tissue (muscle, liver, kidney, etc)

Laboratory Testing

Serum laboratory tests are the most routine way to assess thyroid imbalances. Below is the list of markers commonly used to assess thyroid function. Normal ranges for each marker provided in two separate ranges:

  • Typical lab range: used by most laboratories.
  • Functional range: which is a narrower range that may be useful to identify imbalances earlier and provide higher standard for thyroid function evaluation.

TSH (Thyroid Stimulating Hormone): hormone produced by the pituitary gland (in the brain) and the most common and the most sensitive marker  used to assess thyroid function. More TSH is produced if the Thyroid gland is underactive.

Typical laboratory range: 0.4-4.5 mU/L or 0.5-5.5 mU/L

Normal range (recommended by AACE since 2003): 0.3-3.0

Total T4: measure of both bound and unbound T4 levels. TT4 level decreases in hypothyroidism and increases in hyperthyroidism. T4 is otherwise known as Thyroxine.

Typical laboratory range:4.5-12.5 ug/d

Functional range: 6-12 mU/L

Free T4: measure of free or active T4 levels. Typically, the FT4 level of  is low in hypothyroidism and high in hyperthyroidism.

Typical laboratory range: 0.8-1.7 ng/dl

Functional range: 1-1.5 ng/dl

Please note that a high TSH level even in the presence of a normal level of T4 is sufficient for a diagnosis of hypothyroidism since TSH is the most sensitive marker and abnormities in TSH appear sooner than other markers.

Total T3: hormone produced by the follicular cells of the thyroid gland. T3 is low in hypothyroidism, but mainly is used in the diagnosis of hyperthyroidism or over medication with thyroid hormones containing T3.

Typical laboratory range: 60-181 ng/dl

Functional range: 100-180 ng/dl

Free T3: marker for measuring active thyroid hormones available for the thyroid receptors. Typically, the level of FT3 is low in hypothyroidism and high in Hyperthyroidism.

Laboratory range: 2.0-4.8 pg/mL

Functional range: 2.0-3.0 pg/mL

Reverse T3: FT4 inside the peripheral tissue can convert to FT3 (free and active) and rT3 ( Reverse, inactive) forms. The production of rT3 takes place in cases of extreme stress such as major trauma, surgery or sever chronic stress. High levels of cortisol present in those situations promotes the conversion of T4 to rT3 as opposed to T3. Body inability to clear rT3 is another reason for higher level of rT3.

Typical laboratory range: 90-350 pg/ml

Functional range: 90-350 pg/ml

Thyroid Auto-Antibodies: a positive result can be indicative of auto-immune (the body’s immune system is attacking itself) activity. Depending on the type of the antibody produced, a state of hypothyroid or hyperthyroid is produced.

Thyroid Peroxides Antibody (TPO Ab) or Microsomal Antibody: a positive result may indicate Hashimoto’s disease.

Thyroglobulin Antibodies (Tg Ab): This is not as commonly elevated with autoimmune thyroid conditions as TPO Ab. Tg Ab is also typically measured in regular intervals during thyroid cancer treatment.

Thyroid-Stimulating Hormone Receptor Antibody (TRAb): measured as part of diagnosis process for Hyperthyroidism.

Other tests that might be ordered depending on the special circumstances include: Thyroid-binding Globulin (TGB), T3 Uptake, Resin T3 Uptake, Free Thyroxine Index

Symptoms of Hypothyroidism

Please view our full page discussion of the symptoms of low thyroid function.

Signs of Hypothyroidism

First, for the sake of clarity, the difference between a sign and a symptom is that a sign is normally outside the realm of subjective patient experience (i.e.; fatigue, aches and pains, etc.) and is discovered by the physician during examination. The typical signs of hypothyroidism are:

  • Slow pulse rate
  • Slow or absent reflexes
  • Dry, brittle and thinning hair
  • Skin dryness, flaky and show evidence of acne
  • Decreased/loss of the outer third of the eyebrows
  • Brittle nails
  • Edema ( water retention)
  • Thyroid might be enlarged
  • Hands and feet cold to the touch
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