Low Thyroid Level

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Having a low thyroid level, called hypothyroidism, is a common medical condition. It occurs more commonly in women than men. The majority of people with a low thyroid level will also have an enlarged thyroid gland, or a goiter, but everyone with a goiter may not have a low thyroid level.


Studies have shown that a large number of the US population has laboratory evidence of a thyroid problem; therefore, screening the entire population for a thyroid disorder might not be a bad idea.




Symptoms of a low thyroid level can vary depending upon the age when it is first diagnosed, how long it has been present, and the degree of the thyroid deficiency.


Many of the common symptoms of thyroid hormone deficiency, such as, fatigue, cold sensation when most people feel normal temperature, weight gain, constipation, muscle aches, and menstrual irregularities are also common in people with normal thyroid levels.




The diagnosis of hypothyroidism is made mainly by laboratory testing. There are two forms of hypothyroidism, primary and central hypothyroidism. For simplicity sake, we will focus only on the most common form of low thyroid which is primary hypothyroidism.


Primary Hypothyroidism


Primary thyroid disease is seen in over 95 percent of cases of low thyroid levels. In most cases, the blood level of TSH is the first screening test done to check for thyroid disease. If the blood level of TSH is elevated the lab test should be repeated along with blood level of free T4 to confirm the diagnosis of hypothyroidism.


If the repeat blood level of TSH is still high and the blood level of free T4 is low, the diagnosis of hypothyroidism can be made and replacement thyroid hormone should be started


If the repeat TSH value is still high but the free T4 is normal, the diagnosis of subclinical hypothyroidism is made and thyroid hormone may or may not be prescribed by your physician.  


A TSH level is considered elevated when it is over 4 to 5 mU/L. There is a controversy over what the normal range of TSH should be.




Symptoms of thyroid disease vary in relation to how severe it and  how recent the thyroid change. A low thyroid level is less noticeable and better tolerated when there is a gradual loss of thyroid hormone (as in most cases of primary low thyroid) than when it develops rapidly after the  thyroid is surgically removed or after thyroid medication is suddenly stopped.


Symptoms of a low thyroid level:


-A generalized slowing of many of the important functions of the body will cause many of the common symptoms found with hypothyroidism; symptoms such as fatigue, slow movement and slow speech, feeling cold when most people are normal temperature, constipation, weight gain (but not morbid obesity), and slow heart rate.


Some physical changes of low thyroid level include, having coarse hair and skin, developing a puffy face, enlargement of the tongue, and hoarseness. These changes are often more easily seen in younger patients. In older patients these changes are mistakenly thought to be due to normal aging process.



The skin can be cool and pale in patients with low thyroid because of a decrease in blood flow to the skin. It can be dry and rough. Sweating can be decreased. Skin discoloration can occur. A yellowish tinge may be present when a patient has a condition associated with hypothyroidism called carotenemia. An increase in skin pigmentation can be seen when primary low thyroid is associated with a condition called adrenal failure. Hair may become coarse. Hair loss is also common. Nails can become brittle. Swelling can occur (this is called myxedema). Loss of skin color, called vitiligo, can also occur.



Swelling around the eyes can be present. In people with a history of treated elevated thyroid level, there are different forms of eye abnormalities that can be present such as an exaggerated stare, protrusion of the eyes, and weakness of the eye muscles.



Patients with a low thyroid level have an increased risk of bleeding. They also have anemia (not requiring supplemental iron). Another form on anemia, called pernicious anemia, can occur in 10 percent of patients with low thyroid levels.


Women in the childbearing years may develop an anemia that may require supplemental iron; this is related to excessive bleeding with menstral cycles. In patients with an anemia that requires supplemental iron who also have a low thyroid level, combined therapy with thyroid replacement medication and iron taken by mouth, will result in correction of the anemia, which may not correct with treatment with iron alone.


Heart and Blood Vessels  

Having low thyroid level results in a decrease in the amount of blood that the heart pumps out due to a slower heart beat and a decrease in the strength of the contraction. This results in a decrease in a person’s ability to perform exercise along with shortness of breath with exercise, two common complaints in patients with low thyroid levels.


Heart failure or chest pain can worsen when low a thyroid level develops in patients with heart disease. In these patients, replacement thyroid medication should be given with caution, beginning with a low starting dose (eg, 25 mcg) and then increasing in small amounts every one or two months.


Other abnormalities associated with low thyroid levels can contribute to heart and blood vessel disease:

-Accumulation of fluid around the sac of the heart

-Development of high blood pressure

-Development of high cholesterol


The Lungs

Fatigue, shortness of breath with activity, clear nasal drainage and decreased ability to perform exercise may be related a low thyroid level.


Sleep apnea can occur in patients with a low thyroid level, mainly as a result of an enlarged tongue. Treatment of the low thyroid level will usually reverse the sleep apnea, although some patients may require treatment with a CPAP machine.


Intestinal Disorders 

Decreased movement of the GI tract can result in constipation, one of the most common symptoms seen  in people with a low thyroid level.


Low thyroid levels can cause a decrease in taste sensation. It can also cause atrophy of the stomach lining. This is due to the body’s own antibodies attacking the stomach lining (called pernicious anemia); this can occur in 10 percent of patients with low thyroid levels.


Celiac disease is also a GI tract problem occasionally related to low thyroid levels. It can cause problems with digestion resulting in a chronic diarrhea.


Fertility Issues

Women with a low thyroid levels may have irregular and/or infrequent periods, no periods at all, or heavy periods. In half of the cases, menstral problems can continue even after treatment with thyroid replacement.


Menstrual problems can result in fertility problems. If pregnancy does occur, there is an increased likelihood of an early miscarriage. Women can even develop a condition caused by too much prolactin production. This can lead to lack of periods and even leakage of breast milk.


A decreased sex drive, problems with erections and delayed ejaculation can be a problem in the majority of men with a low thyroid levels. Sperm size and shape are even abnormal in the majority of men with low thyroid levels. This can be corrected in a significant number of cases with thyroid hormone replacement.


Carpal Tunnel 

Carpal tunnel syndrome is a common complication of having a low thyroid level. It is often reversible with thyroid hormone medication.


Muscle or Joint Pains 

Rarely patients with a low thyroid level will develop joint pains, aches, and stiffness. Patients with low thyroid levels can also develop elevated uric acid levels which can lead to more frequent gout flares.


Laboratory Abnormalities

Patients with a low thyroid levels can develop low sodium, evidence of kidney problems, and elevated cholesterol.



A low thyroid level can cause medication to remain in the body for longer periods. Seizure meds, blood thinners, pain and sedative meds, all can remain in the blood stream for longer periods which can result in harmful effects on the body. For this reason, strengths of some medication may need to be reduced with low thyroid levels.




Patients with low thyroid levels may have had past treatment of an elevated thyroid level, either by injection of a radioactive medication or surgical removal of their thyroid. Your doctor may examine you for an enlarged thyroid, also called goiter, or for an old thyroid surgery scar.


Screening blood work can be done to test for a low thyroid levels in people at risk of having thyroid disease. The main benefit of screening is to detect problems before symptoms develop.


Subclinical hypothyroidism is a condition where patients will have laboratory evidence of a low thyroid levels without symptoms of the disease; it is common in the adult population. There is no evidence that early detection and treatment with thyroid replacement medication makes a difference in the long run.


Thyroid replacement medication has few side effects when properly prescribed. Prescribing too much medication is a common error and can be associated with loss of bone density and heart problems, especially in elderly patients.


Risk factors for a low thyroid levels include, having an enlarged thyroid (also called goiter), having a another medical condition where a person’s own antibodies are attacking their body, called an autoimmune disease (an example is vitiligo), having previously had radioactive iodine treatment , having had head and/or neck radiation treatment, or having a family history of thyroid disease.


All people with symptoms consistent with a low thyroid should have their thyroid level tested. Screening people who do not have any symptoms is controversial.


Pregnant women, or women hoping to become pregnant, should also be screened.


Most experts recommend screening for thyroid problems by measuring the blood level of TSH.


Additional factors that may cause your doctor to screen for thyroid disease are:


-Significantly elevated cholesterol

-Low sodium level  

-High blood level of muscle breakdown enzymes  

-Evidence of anemia  

-Fluid within the sac that surrounds the heart or chest cavity

-Previous injection of radioactive medication used to treat an overactive thyroid

-History of neck surgery or radiation therapy

-History of a pituitary disorder

-History of an autoimmune disease


TSH will start to increase when the level of free T4 concentration decreases below the normal level.


Primary thyroid disease accounts for over 95 percent of cases of low thyroid levels. As a result, measurement of blood level of TSH (rather than free T4 or total T4) is an excellent screening test for hypothyroidism.


The TSH level may not be a reliable way to measure for thyroid disease in patients who are hospitalized or in patients with pituitary problems. Screening for thyroid disease in hospitalized patients  can be inaccurate and is not recommended by many experts.




In the majority of cases, hypothyroidism is a permanent medical condition that will require lifelong medication. Treatment consists of daily thyroid hormone replacement. Instances where medication may not be needed would be when the low thyroid level is due to a temporary medical condition, such as, when the thyroid is temporarily inflamed or when low thyroid level is caused by a medication, such as lithium.


The goal of treatment is to bring the thyroid hormone level back to its normal range. This can be done in almost all people with the use of medication such as T4. When medication is used to bring the thyroid back to normal its normal range all of the symptoms and body changes caused by having a low thyroid level will go back to normal.




The most commonly medication used to correct a low thyroid level is T4. Examples include synthroid or levothyroxine. Approximately 80 percent of the T4 medication is absorbed into the body from the GI tract. One dose of T4 will last seven days and will result in a steady level of T4 and T3 in the body.


T4 is not the actual form of the medication that has an effect on the body. T4 gets converted to T3, which is the active thyroid hormone. This conversion process occurs in 80 percent of the total daily production of T3 in normal individuals; as a result, blood levels of T3 will be within the normal range in patients with low thyroid levels who are receiving adequate doses of T4 medication. Providing T4 instead of T3 hormone has advantages because a patient's own body is able to control the amount active medication that gets converted.



Several types of T4 are available. There is a lot of controversy over their differences in strengths. Because there may be subtle differences in strength between T4 medications, experts feel that it is preferable to stay with one formulation when possible.


The medication is available in color-coded tablets. Small increments in hormone content allow for precise adjustment of the dose of the medication according to the blood level of TSH.


Side effects fromT4 replacement are rare as long as the correct dose is given. Rarely, patients will have an allergy to the dye or filler in the tablets. For people with dye sensitivities, multiples of the white 50 mcg tablets can be given.


The average replacement dose of T4 in adults is approximately 1.6 mcg per kg of body weight per day (112 mcg per day in a 70-kg adult). You can convert from lbs to kg by multiplying your weight by 0.45.


T4 should be taken on an empty stomach, ideally an hour before breakfast (few patients are able to wait the full hour).


T4 should not be taken with other medications that interfere with its digestion, such as some cholesterol lowering medication (bile acid resins), heartburn medication (proton pump inhibitors and calcium carbonate), and iron (ferrous sulfate).


The starting dose can be the full anticipated dose (1.6 mcg per kg per day) in young, healthy patients, but older patients should be started on a lower dose (25 to 50 mcg daily).


Patients who are treated with T4 usually will begin to improve within two weeks, but complete recovery can take several months in those with severely low thyroid levels. Although symptoms may begin to go away after two to three weeks, normal blood levels of TSH may not be present for at least six weeks. It is for this reason that your doctor should wait six weeks to check to see if the level of TSH has changed after starting you on medication. If the TSH remains above the normal level, the dose of T4 can be increased by25 mcg per day and a repeat TSH measurement should be done in six weeks.


The goal of treatment is to treat symptoms caused by the low thyroid level and to bring the TSH into a normal range. Another goal is to reduce the large thyroid, also called goiter. This is usually caused by a patient’s own antibodies attacking their thyroid, called Hashimoto's disease. Approximately 50 percent of patients will have some decrease in the size of their thyroid with treatment.


After successful treatment with medication, patients should be examined and their blood level of TSH checked on a yearly basis. The TSH can be checked more often if there is any change in the patient's status.


There following are instances where a different dose of thyroid medication may be needed:


An increase in dosage may be needed

-During pregnancy

-With some GI disorders

-With kidney diseases where protein is spilled into the urine

-With some antibiotics or seizure medication, such as rifampin, carbamazepine, phenytoin, or phenobarbital 


A decrease in dosage may be needed

-As a patient ages

-After giving birth

-After a patient loses weight


Successful treatment can reverse all of the symptoms and body features of low thyroid levels.  Long-term treatment of hypothyroidism is not associated with slowed thinking or depressed mood. There is no evidence that people with treated hypothyroidism die at an earlier age.


In contrast, infants with low thyroid levels at birth or inadequate treatment or delayed treatment for several months, may develop permanent brain damage, even if they are adequately treated several months later.


Because many symptoms of hypothyroidism are not specific, patients often think that their T4 dose is too low when they feel tired or gain weight. The possibility of a low T4 dose should be verified by measuring blood levels of TSH before the dose is increased. The dose of medication should not be changed in patients without symptoms of low thyroid when their level of TSH is only slightly above (or below) the normal range. TSH values may be slightly high (or low) because of laboratory error or normal changes in TSH secretion. For this reason, a slightly high (or low) value should be confirmed with another measurement before the dose is changed.


On the other hand, if a patient has possible symptoms of low thyroid levels, and the blood level of TSH is confirmed by repeat measurement to be at the upper limits or above the normal range, it is reasonable to increase the dose and to aim for a blood level TSH value in the lower half of the normal range.


Giving too much thyroid medication should be discouraged. Taking in too much thyroid medication can cause a number of medical problems. The main risk of having an elevated thyroid level is developing an abnormal heart beat called atrial fibrillation. This abnormal condition occurs three times more often in older patients with too high of thyroid levels as compared to normal patients. Patients with an elevated thyroid level, especially postmenopausal women, may also experience bone loss at a more rapid pace. It is important for patients to be informed on the potential negative effects of taking too much thyroid medication.


Some hypothyroid patients will continue to have symptoms of low thyroid even after they start taking T4 replacement and the TSH has returned to its normal level. For this reason some doctors may prescribe thyroid medication that contains T3 alone or in combination with T4. Examples include, Cytomel (T3 alone), Thyrolar (T4-T3 combination), and Armour®, made from dried pig thyroid glands (a mixture of T3 and T4).


For most patients with hypothyroidism, experts do not recommend treatment with T3-containing medications. Patients treated with T3-containing medications have wide fluctuations in blood level of T3 throughout the day due to its rapid gut absorption and it only remains in the body for about a day.


Temporary treatment with T3 is appropriate in some patients with thyroid cancer who are about to undergo certain tests or who are receiving treatment for their medical condition. To shorten the period of low thyroid levels, a doctor may stop a patient's T4 medication and substitute it with T3 for 3 to 4 weeks until the T4 is cleared.


Special Situations 


There are several situations in which medication should be given more conservatively or the dosage may need modification:


Older patients or those with heart disease

Thyroid hormone increases the work of the heart. This can cause a small risk of abnormal heart beats, chest pain, or a heart attack in older patients.


Older patients (older than 50 or 60 years depending on their medical problems) should initially be treated with 50 mcg T4 per day. Those who have a history of heart disease should initially be treated with 25 mcg per day. In either group the dose can be increased by 25 mcg per day every three to six weeks until replacement is complete, as determined by a normal blood level of TSH concentration, or an increase in dose results in heart-related symptoms, in which case something less than full replacement may have to be accepted.



Women need more thyroid hormone during pregnancy and, unlike normal nonpregnant women, those with low thyroid levels are not able to increase their level of T4 and T3 secretion. Approximately 75 to 85 percent of women with preexisting low thyroid levels will need a higher dose of T4 during pregnancy to maintain normal TSH range. The increase in T4 requirements begins at about eight weeks and peaks by week 16 to 20 weeks of pregnancy.   


Estrogen Replacement

In women receiving T4 replacement and who are also taking in estrogen, they can have an increased need for T4. Blood level of TSH should be measured approximately 12 weeks after starting estrogen in women receiving T4 therapy to determine if an increase in T4 dose is needed.


Food and Drinks

A high-fiber diet is another factor that can interfere with the absorption of T4. Fiber pills taken by mouth are not thought to affect the absorption.


Coffee, in comparison to water, reduces the absorption of thyroid medication by 27 to 36 percent.


Poorly Compliant Patients 

Some patients who do not take their T4 regularly, even though they have been counseled many times by their doctor, may be given their total weekly dose of T4 once per week. Weekly dosing should probably not be used in patients with heart disease.


Thyroid cancer 

Patients who have had their thyroid removed after having thyroid cancer, with or without radioactive destruction of the thyroid, will need to take T4 not only for treatment of the low thyroid level, but also to prevent recurrence of their thyroid cancer. T4 treatment will need to be life-long in these patients and should not be stopped even if there is enough normal thyroid tissue remaining to provide an adequate hormone level.


Other Uses of Thyroid Medication


Occasionally doctors will give thyroid hormone to patients with normal thyroid levels. An example would be in patients who are undergoing heart bypass surgery, those with difficult to treat depression, and for weight loss.  For-the-most-part, most doctors do not prescribe thyroid hormone replacement for anything other than replacing a laboratory confirmed low thyroid level. Use of thyroid medication to treat any other condition is not considered to be a generally accepted medical practice. 


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