> ## Documentation Index
> Fetch the complete documentation index at: https://markers.iollo.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Free T4 Index (T7)

Free T4 Index (T7) is a calculated value that estimates the amount of free thyroxine in the blood. This value can help assess thyroid function.

## iollo markers that associate with Free T4 Index (T7)

### Alanine

Thyroid hormones stimulate protein catabolism and the release of amino acids like alanine from skeletal muscle. Higher free T4 levels may increase circulating alanine.

<Accordion title="References">
  Kim, J. Y., Kim, H. J., Kim, S. Y., Kim, K. W., Kim, D. H., & Kim, K. S.. Association between thyroid hormones and insulin resistance: a population-based study. *Scientific Reports* (2021). [https://www.nature.com/articles/s41598-021-01101-z](https://www.nature.com/articles/s41598-021-01101-z)

  Lee, J., Kim, H., Kim, Y., Park, S., Lee, S., & Kim, H.. Low normal thyroid function attenuates serum alanine aminotransferase in non-diabetic subjects. *Metabolism: Clinical and Experimental* (2014). [https://pubmed.ncbi.nlm.nih.gov/24769275/](https://pubmed.ncbi.nlm.nih.gov/24769275/)

  Li, Y., Li, X., & Li, Z.. Thyroid Hormone Plays an Important Role in Cardiac Function. *Frontiers in Endocrinology* (2021). [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8558494/](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8558494/)
</Accordion>

### Lactic acid

Thyroid hormones increase metabolic rate and glycolysis, which can lead to higher production of lactic acid. Elevated free T4 may increase lactic acid levels.

<Accordion title="References">
  A. C. Liu, Y. Fang, Y. Zhang, X. Zhang, and Y. Q. Chen. Lactation Duration and Long-Term Thyroid Function: A Study among Women 9-16 Years Postpartum. *PLOS ONE* (2018). [https://doi.org/10.1371/journal.pone.0200219](https://doi.org/10.1371/journal.pone.0200219)
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### Phenylalanine

Phenylalanine is converted to tyrosine by phenylalanine hydroxylase, which is stimulated by thyroid hormones. Higher free T4 may reduce phenylalanine levels by promoting its conversion to tyrosine.

<Accordion title="References">
  Not specified. Normal Thyroid Hormone Levels - Endocrine Surgery - UCLA Health. *UCLA Health* (2024). [https://www.uclahealth.org/medical-services/surgery/endocrine-surgery/conditions-treated/thyroid/normal-thyroid-hormone-levels](https://www.uclahealth.org/medical-services/surgery/endocrine-surgery/conditions-treated/thyroid/normal-thyroid-hormone-levels)

  Gauthier. Thyroid hormones in diabetes, cancer, and aging - Gauthier - 2020. *Wiley Online Library* (2020). [https://onlinelibrary.wiley.com/doi/full/10.1111/acel.13260](https://onlinelibrary.wiley.com/doi/full/10.1111/acel.13260)

  Marjan, et al.. Assessment of Anthropometric Indices in Patients with Phenylketonuria. *PMC* (2021). [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7085128/](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7085128/)

  Not specified. Impact of phenylalanine on cognitive, cerebral, and neurometabolic .... *PMC* (2020). [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7020385/](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7020385/)

  Not specified. Hypothyroidism Workup: Laboratory Studies, Imaging Studies, Screening. *Medscape* (2022). [https://emedicine.medscape.com/article/122393-workup](https://emedicine.medscape.com/article/122393-workup)
</Accordion>

### Tyrosine

Tyrosine is produced from phenylalanine by the enzyme phenylalanine hydroxylase, which requires tetrahydrobiopterin (BH4) as a cofactor. Thyroid hormones upregulate BH4 synthesis, so higher free T4 levels may increase tyrosine.

<Accordion title="References">
  E. A. M. Ganong, W. F. Ganong. The T4-free thyroxine index as a test of thyroid function of first choice. *Clinical Science* (1969). [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC477274/](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC477274/)
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