FT4 [Free T4] blood tests are ordered to measure thyroxine levels that are in the blood. Depending on what the test results happen to be, it can be used to evaluate how well a person’s thyroid is functioning and potentially diagnose the presence of a disease. It is usually ordered after someone has been given the TSH blood test and it has come back as being abnormal.
T4 is often tested at the same time after the TSH blood test with another hormone that is called T3. Together these hormones help to control how the body utilizes energy every day. When more FT4 is released by the thyroid gland or the opposite occurs, then bothersome signs and symptoms will begin to appear over time. The two main issues that the FT4 blood test will discover are hyperthyrodism or hypothyroidism.
It can also be used to detect fertility issues, diagnose issues with the pituitary gland, or monitor the effectiveness of a treatment plan that is correcting a problem with the thyroid gland. It may also be used to monitor a thyroid cancer diagnosis.
When To See a Doctor
If you are experiencing the signs and symptoms of an overactive or underactive thyroid gland, then it is time to speak with a medical provider about the FT4 blood test.
The symptoms of an overactive thyroid gland may include tremors in the hands, a general feeling of weakness, and unexpected weight loss. A faster than normal pulse is usually experienced and some people may experience bouts of anxiety or panic attacks. The eyes may also be affected and appear to be puffy, dry, or irritated. Some people may have changes in vision or be sensitive to the light.
In comparison, the symptoms of an underactive thyroid gland are generally weight gain because of a lack of energy. There may be an increased feeling of fatigue that results in a desire to nap often throughout the day. Dry skin is also common, as are changes in bowel habits. Some people may experience a heightened intolerance of cold weather, experience hair loss in various locations on the body, and have skin that feels swollen or puffed out.
What Do My Test Results Mean?
Most people will have their FT4 blood test results compared to their TSH and FT3 blood tests to determine a potential diagnosis. Here are some interpretations that a medical provider may make based on all three test results that are received back.
- Mild levels of hypothyroidism are generally suspected when TSH levels are high, but FT4 and FT3 levels are normal.
- When FT3 levels are low, but TSH levels are high, then this is a strong indication of hypothyroidism.
- Normal FT3 and FT4 levels with low TSH results may indicate a mild form of hyperthyroidism.
- Low levels of TSH that are paired with high levels of FT4 and FT3 indicate hyperthyroidism.
- High both FT3 and FT4 is high, but TSH is normal, then this indicates the presence of a genetic issue.
Some people may receive their results back and be told that all of their readings were low. This means that there is an illness that is not associated with the thyroid gland causing the signs and symptoms. It may also indicate a rare form of hypothyroidism that is caused by the pituitary gland, referred to as secondary hypothyroidism.
Here’s What You Need To Know
Certain medications or health conditions can cause a false positive result on the FT4 blood test. This is especially true for women who are taking an estrogen supplement or are taking oral contraceptives. Someone with liver disease may have high levels of FT4, as can someone who has a systemic illness that is either acute or chronic in nature. Aspirin therapies may also produce inaccurate results.
In general, however, FT4 levels are not usually affected by medications, but they can be in rare instances. If test results come back as abnormal, even when taking these medications, a medical provider may feel comfortable in proceeding toward a diagnosis.
Lifestyle changes will not usually affect FT4 levels either. If not enough FT4 is being produced, replacement medication and routine testing may occur to determine if the treatment plan is being effective.
The FT4 blood test is not usually ordered on its own, but the results explained here can help a medical provider begin to determine the source of bothersome symptoms that may be happening. Schedule an appointment to discuss your symptoms or results so a treatment plan can be developed to meet your needs.
