Thyroid profile: free T3, free T4 and TSH
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|Test||Thyroid profile: free T3, free T4 and TSH|
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Please, make sure you have read When not to use this website to ascertain whether having this test is an appropriate and safe course of action for you.
This test measures the amount of thyroid stimulating hormone (TSH) as well free T4 and free T3 in the blood serum.
There are three common ways in which there may be inadequte amounts of the thyroid hormone for normal metabolism. The one which all doctors are aware of is primary hypothyroidism, in which there is a raised TSH and a low T4 and low T3. This is due to failure of the thyroid gland itself, possibly due to autoantibody disease, possibly due to toxic stress or possibly due to iodine deficiency.
The second, and in my view the most common cause of thyroid failure, occurs at the pituitary level. In this condition there is inadequate thyroid stimulating hormone (TSH) produced from the pituitary and so one tends to see low or normal TSHs, low T4s and variable T3s. This condition I see most commonly in my patients with chronic fatigue syndrome, where there is a general suppression of the hypothalamic-pituitary-adrenal axis.
The third type of under-functioning is due to poor conversion of T4 to T3. This requires enzymes and co-factors, in particular selenium, zinc and iron. In this condition there are normal or possibly slightly raised levels of TSH, normal levels of T4 but low levels of T3. This requires micronutrients and also T3 to correct.
Therefore, in any patient in whom I suspect a thyroid problem I now routinely ask for a TSH, a Free T4 and a Free T3 in order to gain the full picture.
Important message to non-patients wishing to have thyroid hormones prescribing
If you have a thyroid function test via my website and the results indicate a need for thyroid supplementation, then I will first ask your GP to consider prescribing this for you in my letter of interpretation.
If your GP is not willing to prescribe thyroid hormones, then I would be able to do so, ON THE CONDITION THAT either your GP or a thyroid specialist agree to monitor your thyroid function regularly to check that you remain EUTHYROID; that is to say, you do not have any symptoms of thyrotoxicosis. These symptoms and signs would be: racing pulse, tremor, undue anxiety, undue sweating, irritability, unexplained weight loss, unexplained loss of muscle, unexplained osteoporosis, bulging eyes (exophthalmos) or unexplained goitre. Before I can start prescribing thyroid hormones, I would need written assurance either from your doctor (NHS or private) that he will be monitoring you clinically or from you confirming that you have such a doctor who is happy to monitor you.
If you cannot find a doctor who can state that you are euthyroid, then you would need an hour's appointment (currently £275) with me here in Mid Wales to initiate thyroid hormone prescribing, OR I would refer you to a local specialist.
Please bear all of this in mind when ordering this test.
For treatment recommendations see Hypothyroidism.
This test is performed on a blood sample
The kit for this test includes a gold topped serum blood tube, a plastic bag in which the blood tube need to be sealed, a request form and a pre-paid envelope for sending the sample to the laboratory.
Have the blood taken and put in the blood tubes, make sure that your name and date of birth are clearly marked on the tube. Check that your details are correct on the request form. Place the samples in the plastic bag and seal the top ready for posting in the pre-paid addressed envelope. Please, make sure that the request form is sent along with the samples.
Any patients who are taking T3 as part of their thyroid supplement need to have their T3 levels monitored as well as T4. T3 is much more quickly metabolised than T4 and blood tests should be done between 4-6 hours after their morning dose. If the appointment does not fit in with the morning dose, adjust the timing of the dose so it does! Please let me have the details of your GP and any diagnoses which you have been given so that I can write to him/her with the results of the test and my comments and suggestions for management. If you are already on thyroid hormones, please let me know the dose - you need to take your normal dose on the day of testing.