The diagnosis of hypothyroidism is based on the patients history, clinical examination and the lab tests.
A. Patients history
The history that is obtained from the patient will aid in the diagnosis of hypothyroidism.
It is very important to find out if the patient has risk factors for developing hypothyroidism.
Risk factors for hypothyroidism include:
- Gender – females have a higher risk than males.
- Age – increasing age increases the risk of hypothyroidism.
- Race – asian are at a higher risk.
- Location – if you are staying at in a region with low levels of iodine such as some parts of Southeast Asia and Africa.
- History of having any autoimmune condition such as : type 1 diabetes, rheumatoid arthritis, vitiligo, pernicious anemia, addison’s disease, multiple sclerosis, celiac disease.
- History of any radiation given to head and neck for therapeutic reasons.
- History of use of medicines which can affect the thyroid gland.
- Any close family member suffering from thyroid problems or any auto immune conditions.
- Patient with certain disorder have a higher risk these are:
- – Patient of bipolar disorder
- – Down’s syndrome patient
- – Turner syndrome patient
- – Goiter or enlarged thyroid gland
Then the history will also contain the symptoms that the patient will experience
Excessive sleepiness, tiredness, excessive weight gain, muscles pain and cramps, feels colder than others around, hair fall or thinning of hair, dry skin, increased size of the neck or noticing neck swelling, history of constipation, if patient is a female she will give history of Irregular menstrual cycles.
B. Clinical examination for diagnosis of hypothyroidism.
It is the examination of the patient which is done by a medical practitioner.
The positive findings in these patients will be:
Increased BMI
Dried scaly skin
decreased heart rate
Increased size of the thyroid gland in this case the doctor will palpate the gland to find out more about the swelling or the nodule eg. What is its consistency, does it move with swallowing, does it cause any pressure symptoms etc.
C. Lab tests-Blood tests
1. TSH (thyroid-stimulating hormone)
- In hypothyroidism the levels of TSH are very high.
- The reason behind increased TSH is, TSH is secreted by the pituitary gland. Normally this TSH acts on the thyroid gland and will cause the thyroid hormone secretion.
- The pituitary gland contains cells which are sensitive to high or low thyroid levels.
- When the blood flows through the pituitary gland these cells sense the thyroide hormone level in the blood.
- When there occurs increase or decrease in the thyroid hormone levels these cells signal the pituitary gland to decrease or increase the TSH secretion respectively.
Summary:
- When the thyroid hormone is less, more TSH is released to stimulate the gland more in order to produce more thyroid hormone.
- But in case of primary hypothyroidism where the defect is in the thyroid gland, the gland does not respond to the increased TSH levels.
- So the thyroid hormone remains low and the pituitary will keep on secreting TSH to try and increase the thyroid hormone levels.
- This is why the TSH levels are high in case of primary hypothyroidism.
- In the case of secondary hypothyroidism where the thyroid gland is absolutely normal and the defect lies in the pituitary or the hypothalamus resulting in decreased TSH secretion which in turn result in reduced thyroid hormone levels.
- Therefore when TSH levels come normal or low the thyroid hormone levels should be evaluated before ruling out hypothyroidism.
INTERPRETATION OF TSH LEVELS.
| |
TSH levels in milliunits per liter | Interpretation |
0.4 mU/L | Normal |
2.5 mU/L | At risk of hypothyroidism |
4.0 mU/L | Mild hypothyroidism |
10.0 mU/L | Hypothyroidism. |
The reference range for TSH levels is 0.4 mU/L to 4.0 mU/L.
NOTE: This reference range is not fixed and will vary from laboratory to laboratory and from person to person.
2. Free Thyroxine (T4)
- As we mentioned earlier that a person may have hypothyroidism with normal TSH levels as seen in secondary hypothyroidism.
- In such cases we have to evaluate the serum thyroxine levels.
- The thyroxine (T4) level that we evaluate is the free T4 level.
- Free T4 in the blood is the thyroxine that is available for the tissues for its use.
INTERPRETATION OF TSH AND FREE T4 LEVELS | ||
TSH levels | Free T4 levels | Interpretation |
high | ¯ low | Primary hypothyroidism |
high | normal | Subclinical hypothyroidism |
¯ low or normal | ¯ low or normal | Secondary hypothyroidism |
The normal range of free T4 is 5 to 13.5 mg/ dl (micrograms per deciliter.
NOTE: The normal range may vary from laboratory to laboratory and from person to person.
Analysis of tsh levels for diagnosis of hypothyroidism
3. TPO Antibodies (Anti-thyroid Microsomal Antibodies Testing)
- Most common cause of hypothyroidism is the auto immune disease that is
- In autoimmune diseases the body’s immune cells bodies attacks its own cells and causes destruction of tissues in the body, in Hashimoto’s thyroiditis thyroid cells are damaged.
- The immune cells produce antibodies against self.
- In thyroid the antibodies which are produced are the thyroid peroxidase antibodies (TPO antibodies) which attacks the thyroid peroxidase enzyme which is required in 2 important steps in thyroid hormone formation that is: 1) step of oxidation where 2 molecules of iodide to iodine and 2) step of conjugation where the 1 or 2 molecules of iodine binds to the thyroglobulin and form monoiodotyrosine (MIT) or diiodotyrosine (DIT) respectively.
- As autoimmune disease hamper both these steps it causes hypothyroidism.
- The antibodies slowly attack the thyroid gland, so hypothyroidism tends to develop gradually.
- It may even take years for the thyroid function to decline for a person to become hypothyroid.
- Which means that, there will be a time when the patient will be positive for TPO antibodies and still have normal thyroid function.
- In some cases patient may never progress to become
- Therefore the patient will not be started on thyroid hormone replacement medication if the patient is positive for TPO antibodies but TSH is within the normal
- These patients are monitored over time by doing yearly TSH levels to see for the disease progression.
D. Imaging methods for diagnosis of hypothyroidism.
- Imaging is not the first line of diagnosis of hypothyroidism.
- Imaging has a role when there in enlargement of thyroid gland or if there is presence of nodules in the thyroid gland, in such cases imaging like ultrasound may be required to determine the size of the nodule and to rule out cancer.
- Imaging may also be useful in secondary hypothyroidism where in the cause of hypothyroidism lies in the hypothalamus or the pituitary gland.
- The hypothalamus or the pituitary gland may be damaged from tumors, infections, radiation,or infiltrative diseases like sarcoidosis which may be diagnosed by CT or MRI of the brain.