How to interpret Thyroid test results
June 25, 2020
In this article, you will learn more about thyroid function, thyroid hormone actions, lab values and how to interpret a complete thyroid panel.
Hypothyroidism: How to interpret Thyroid test results
Thyroid diseases have a prevalence of up to 10% of the population, and hypothyroidism and sick euthyroid syndrome are of particular interest due to their direct impact on patients' quality of life. Understanding the regulation of this endocrine system and therapeutic alternatives are crucial to making appropriate decisions in conjunction with your doctor. A blood test can expose undetected thyroid problems.
In this article, you will learn more about Thyroid gland function, thyroid hormone actions, and Laboratory values and how to interpret a complete thyroid panel. You will also begin to understand the importance of having all of your laboratory data to assess thyroid function. We will explain the diagnosis and treatment of hypothyroidism and share tips on supplements and dietary habits to promote a healthy thyroid.
Thyroid function: a complex endocrinological system
The thyroid is an endocrine gland located in the lower, anterior part of the neck. It is responsible for the formation and secretion of thyroid hormones, as well as iodine homeostasis. Under normal circumstances, the thyroid is under the command of the hypothalamic-pituitary axis (TRH -> TSH -> thyroid gland), and produces two types of hormones:90% inactive thyroid hormone, called thyroxine or T4and 10% active thyroid hormone, triiodothyronine, or T3.
The inactive hormone T4 is converted in peripheral tissues into active T3 hormone, or, by an alternative mechanism, into inactive T3 hormone (known as "reverse T3" or T3r).
A balance of thyroid hormones is essential for proper metabolic function. T3 plays a critical role in regulating the activity of virtually all nucleated cells in the human body.
In the field of nutrition, the importance of the thyroid gland is usually mentioned concerning the control of the basal metabolic rate. (BMR): increased consumption and oxidation of glucose, fatty acids, and, by extension, weight loss.
It is a common myth that hypothyroidism is a direct cause of weight gain
Based on scientific publications, a decreased thyroid function predisposes to weight gain due to a decrease in metabolic rate and physical activity, but not in eucaloric conditions (adequate caloric intake, neither more nor less, to maintain your weight).
Less well-known functions of thyroid hormones include control of cardiac output and resting heart rate, control of the respiratory rate at rest, promotion of the oxygen supply to the tissues and bone development after birth, and bone remodeling. Thyroid hormones are involved in the stimulation of the nervous system, alertness and wakefulness, reproductive health, and regulation of other endocrine organs and pituitary functions.
Sick euthyroid syndrome: "unexplained tiredness."
To start with, we will focus on systemic non-thyroid disease or "sick euthyroid syndrome."
We will focus on the situation in which one is halfway between an adaptive physiological response and pathology. The treatment is not part of your GP's clinical protocol. It could be a challenge for your GP to interpret; an endocrinology specialist will be more familiar with different therapeutic approaches.
Alterations characterise the sick euthyroid syndrome in the circulating thyroid hormone concentrations without there being real involvement at the thyroid level. The causes include physiological stress, serious illness, and trauma.
At the laboratory, we can identify a precise diagnosis (although it could be confused with central hypothyroidism, so the clinic should guide us to the diagnosis!). A constant finding is a decrease in the production of active T3 by inhibition of 5'-monodeiodination of T4, always linked to increased reverse (inactive) T3 hormone. The total T4 concentration is at normal or low levels in more severe patients, and the TSH can be normal or low.
In true hypothyroidism, we usually find a marked increase in TSH as the diagnostic key. Although not further expanded upon, the possible causes are in the management of critical patients (Intensive Care Unit) with severe trauma, myocardial infarction, chronic kidney disease, diabetic ketoacidosis, cirrhosis, thermal injuries, and sepsis. Sometimes hypothyroidism is also seen in starvation, anorexia nervosa, and protein-calorie malnutrition, which can occur outside of a hospital context.
Treatment of diseased euthyroid syndrome is to resolve the underlying disorder, and thyroid hormone replacement is inappropriate. Patients with slightly elevated TSH levels should be monitored over time for overt hypothyroidism.
A complete thyroid panel provides us with all the information necessary for correct surveillance and diagnosis, so if we detect a problem and take the steps needed to solve it, we will repeat the analysis of thyroid function within a period of six to twelve months.
Do keep in mind that an abrupt and prolonged weight loss, with an aggressive dietary caloric deficit, will decrease the active T3 hormone, to a greater or lesser extent. This decrease in the active T3 is an adaptive, evolutionary, physiological response aiming to conserve energy, decrease the production of "unnecessary" heat, and reduce involuntary physical activity.
The decrease in T3, and the increase in reverse T3, reverts rapidly after reintroducing enough calories. During a short intermittent fast, less than 24 hours, as in Ramadan, for example, no significant alterations of thyroid hormones are observed. If we consider a longer fast or significant caloric restriction to address a weight problem therapeutically, we must take stock of the numerous benefits that weight loss provides, as well as the potential complications, in consultation with your regular GP.
In hypothyroidism, we find a lack of the action of the thyroid hormone in the tissues of the body. The cause may be in the thyroid, primary hypothyroidism (95% of cases), from the pituitary, or of hypothalamic origin (5% of cases).
Globally, the most frequent cause is iodine deficiency, although the WHO considers the UK one of the countries with adequate intake. In our setting, however, the most frequent etiology is autoimmune (Hashimoto's Thyroiditis).
Note: if you are taking drugs such as lithium, amiodarone, antithyroid, or tyrosine kinase inhibitors, these should be considered as a secondary cause of hypothyroidism.
In an adult, the symptoms are slow and progressive onset. It starts with fatigue, lethargy, constipation, cold intolerance, myopathy, carpal tunnel syndrome, and menstrual disorders, in addition to weight gain, dry and rough skin, deep voice, and possible sleep apnoea.
Since the symptoms are nonspecific, the diagnosis is made based on laboratory tests. However, the differential diagnosis may require the determination of anti-thyroid peroxidase (anti-TPO) and anti-thyroglobulin (anti-TG) antibodies, which are positive in 90-100% of autoimmune thyroiditis.
Below is a table that summarises the alterations in the thyroid panel of the different thyroid diseases:
Free T4: Low.
Free T3: Low.
Free T4: Normal.
Free T3: Normal.
Non-thyroid systemic disease (diseased euthyroid syndrome)
TSH: Low / Normal.
Free T4: Low / Normal.
Free T3: Low and rT3 High
TSH: Low / Normal.
Free T4: Low.
Free T3: Low.
Free T4: Normal.
Free T3: Normal.
Free T4: High.
Free T3: High.
TSH: Normal / High.
Free T4: High.
Free T3: High.
Which supplements are relevant, and which lifestyle interventions work?
A decrease in thyroid function may be associated with an increase in cortisol, the body's primary stress hormone, secreted by the adrenal glands. A constant elevation of cortisol suppresses thyroid function and causes a cascade of events leading to insulin resistance, increased appetite, and increased adipose tissue.
To reduce chronic stress, consider optimizing one of these points:
1. Nutrition and physical exercise are the primary keys to maintain a healthy metabolism. Find a weight loss and physical activity program that you can sustain over time. To gradually lose weight, implement a moderate daily calorie deficit (10-20%). If you are not exercising, a brief and straightforward strength/weight training routine, an increase in your cardiovascular activity, or a combination of both (for example, 30 minutes each, 2 or 3 days a week, depending on your physical abilities starting) is enough to receive benefits.
2. Improve your sleep hygiene: at least eight hours of sleep per night, especially if your TSH levels are high. Weight gain and metabolic dysfunction are both correlated with sleep deprivation.
3. Limit the consumption of caffeine and alcohol.
4. Explore techniques such as meditation, yoga, breathing exercises, or progressive muscle relaxation.
5. Concerning nutrition and an adequate intake of minerals, iodine is the primary nutrient required for the synthesis of thyroid hormones, followed by selenium. Likewise, iron, vitamin A and zinc play an important role. In the case of normal thyroid function, consume a varied diet that includes these nutrients and, if you detect insufficiency in any of them, consider supplementation.
6. If you have hypothyroidism, include foods rich in iodine, fish and seafood, and plant foods rich in antioxidants. Avoid excessive consumption of salt and goitrogenic foods (cauliflower, cabbage, broccoli, radish, and rape, among others of the Brassica genus).
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