Free Thyroxine Index
FTI
Description
"Free Thyroxine Index (FTI)" test estimates the amount of active thyroxine (T4) in your blood by combining total T4 levels with thyroid-binding capacity. Doctors often use this test to evaluate suspected hypothyroidism or hyperthyroidism and to monitor ongoing treatment. A low FTI may point to underactive thyroid function or protein-binding issues, while a high result can indicate hyperthyroidism. Tracking FTI over time helps guide medication adjustments and supports better thyroid and metabolic management.
Test Category
Hormones
Procedure
Invasive
Sample Type
Blood – Serum
Units
Ratio
Procedure Category
Blood Draw
Test Group
Complete Thyroid Group
Test Group Description
Complete Thyroid Group: A comprehensive array of tests for a thorough evaluation of thyroid function, providing detailed insights into thyroid health and associated conditions.
Optimal Range
For All Individuals:
Conventional Unit: 1.7–4.6 R
SI Unit: Not Applicable
Normal Range
For All Individuals:
Conventional Unit: 1.2–4.9 R
SI Unit: Not Applicable
Results That Differ From The Norm (Direct and Indirect Causes)
Increased levels may indicate:
Benign pituitary tumor (Noncancerous growth of the pituitary gland)
Excess dietary iodine
Graves' disease (Autoimmune disorder causing overactive thyroid)
Hyperthyroidism (Overactive thyroid gland)
Supplemental iodine (Additional intake of iodine through supplements)
Thyroid nodule (Abnorm...
Key Reasons For Testing
Thyroid Function Evaluation: The Free Thyroxine Index (FTI) assesses thyroid hormone activity, providing a reliable measure of thyroid health.
Diagnosis of Thyroid Disorders: Aids in identifying conditions like hyperthyroidism, hypothyroidism, and thyroid hormone resistance.
Hormone Monitoring: Tracks changes in thyroid hormones, ensuring proper function and effective management.
Treatment Effectiveness: A...
Health Status Conditions It May Be Used To Assess
Currently, this test is not directly associated with any conditions listed on the Health Status page. However, it may be included as part of a broader set of tests linked to specific health conditions.
Some Prominent Medical Labs That May Offer This Test
Please note that this particular test has not been associated with any of the listed prominent medical labs. We recommend enquiring with your private physician or nearest hospital to determine where this specific test can be performed.
References
Important Note
Any medical procedure yielding results outside the norm may be directly or indirectly linked to the conditions outlined on this page. Various factors, including genetics, medication and supplement usage, recent illnesses, pregnancy, pre-test eating, smoking, and stress, can impact the test's outcome. Additionally, factors like false positives, false negatives, inaccurate analyses, and others can influence results.
Reference ranges, which help healthcare professionals interpret medical tests, may vary depending on age, gender, and other factors. They may also differ between laboratories due to variations in instruments and methods used. Optimal ranges are designed for preventive purposes, aiming to identify trends and potential risks early, while normal ranges reflect conventional laboratory values indicating no current disease or pathology. Your healthcare practitioner may have specific reasons for testing that deviate from the usual or may interpret results differently based on individual circumstances. Proper interpretation typically involves considering clinical findings and other diagnostic tests. Hence, it is crucial to provide your healthcare professionals with a comprehensive medical history, consult with them for result interpretation, and follow their guidance for potential re-testing or additional diagnostics.
Disclaimer
This content is provided solely for informative and educational purposes. It is not intended as a substitute for medical advice or treatment from a personal physician. Regarding the interpretation of their medical test results and/or specific health questions, it is recommended that all readers and viewers consult their physicians or other qualified health professionals. The publisher is not responsible for any adverse health effects that may result from reading or following the information in this educational content. Before beginning any nutrition, supplement, or lifestyle program, all viewers, especially those taking prescription or over-the-counter medications, should consult their physician or health care practitioner.
Please note that while prominent lab names are included in this content, we cannot guarantee that these labs offer all the tests mentioned. For confirmation, individuals should contact the labs directly or consult their medical practitioners. The information provided reflects general knowledge at the time of publication and may not include recent updates or emerging research. Readers should verify details with qualified professionals to ensure the most up-to-date and accurate guidance.
[1] Pantalone KM, Hatipoglu B, Gupta MK, Kennedy L, Hamrahian AH. Measurement of Serum Free Thyroxine Index May Provide Additional Case Detection Compared to Free Thyroxine in the Diagnosis of Central Hypothyroidism. Case Rep Endocrinol. 2015;2015:965191.
[2] Hennessey JV, Jackson IM. The interface between thyroid hormones and psychiatry: diagnostic and therapeutic issues. Thyroid. 1996;6(6):639-646.
[3] Stockigt JR. Free thyroid hormone measurement: a critical appraisal. Endocrinol Metab Clin North Am.2001;30(2):265-289.
[4] Spencer CA. Clinical utility and cost-effectiveness of sensitive thyrotropin assays in ambulatory and hospitalized patients. Mayo Clin Proc. 1988;63(12):1214-1222.
[5] Abuid J, Larsen PR. Triiodothyronine and thyroxine in hyperthyroidism: comparison of the free thyroid hormone levels in serum and the clinical status of the patient. J Clin Invest. 1974;54(1):201-208.
[6] Ain KB, Refetoff S, Fang SL, Aronin N, Rapoport B. Clinical and molecular aspects of thyroid hormone transport proteins. Thyroid. 1993;3(3):241-249.
[7] Baloch Z, Carayon P, Conte-Devolx B, et al. Laboratory medicine practice guidelines: laboratory support for the diagnosis and monitoring of thyroid disease. Thyroid. 2003;13(1):3-126.
[8] Fisher DA. Physiological variations in thyroid hormones: physiological and pathophysiological considerations. Clin Chem. 1996;42(1):135-139.
[9] Kaplan MM. Monitoring thyroxine therapy. N Engl J Med. 1994;331(26):1743-1744.
[10] Samuels MH. Central hypothyroidism: diagnostic challenges. Endocrinol Metab Clin North Am. 2009;38(2):389-403.
[11] Sapin R, d’Herbomez M. Free thyroxine measured with equilibrium dialysis and nine immunoassays decreases in late pregnancy. Clin Lab. 2003;49(9-10):551-554.
[12] Wartofsky L, Dickey RA. The evidence for a narrower thyrotropin reference range is compelling. J Clin Endocrinol Metab. 2005;90(9):5483-5488.
[13] Mandel SJ, Larsen PR, Seely EW, Brent GA. Increased need for thyroxine during pregnancy in women with primary hypothyroidism. N Engl J Med. 1990;323(2):91-96.