Thyroxine (T4 / FT4)
Clinical interpretation, reference ranges, and thyroid status evaluation for Thyroxine (T4/FT4) under ATA 2017 standards.
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Article Editorial Timeline
Intelligent Context-Aware Learning Path
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Quick Reference Facts
Laboratory Interpretation Workflow
1. Clinical Indication
Ordering protocols based on clinical indications, presenting symptoms, or screening guidelines.
Clinical Pearl: Order when screening for primary organ dysfunctions or monitoring active treatment efficacy.
Test Description & Overview
Thyroxine (T4): The primary prohormone synthesized and secreted by the thyroid gland follicular cells, circulating mostly bound to thyroxine-binding globulin (TBG). Free T4 (FT4) represents the metabolically active, unbound fraction (0.03%).
Free T4 (FT4): 0.8 - 1.8 ng/dL (10 - 23 pmol/L); Total T4: 4.5 - 11.2 mcg/dL (58 - 144 nmol/L).
Elevated (High) Values
- Primary Hyperthyroidism (Graves' Disease, Toxic Nodular Goiter)
- Subacute Granulomatous (de Quervain's) Thyroiditis (Release Phase)
- Exogenous Levothyroxine Overdose or Pituitary TSH-Secreting Adenoma
Decreased (Low) Values
- Primary Hypothyroidism (Hashimoto's Thyroiditis, Post-Ablation)
- Secondary / Central Hypothyroidism (Pituitary or Hypothalamic Failure)
- Severe Myxedema Coma (Profound Low FT4 with Hypothermia and Altered Sensorium)
Clinical Alignment & Significance
Free T4 (FT4) combined with TSH is the primary diagnostic pair for thyroid disease; low FT4 with elevated TSH confirms primary hypothyroidism, while low FT4 with low/normal TSH indicates central hypothyroidism requiring pituitary imaging.
Diagnostic Guidance Notice
Standard laboratory reference ranges vary based on the testing facility. Significant deviations require immediate clinician review to rule out severe medical pathology.
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Reference Citations & Evidence Sources
Clinical Guidelines & Consensus Statements
Clinical Reviews & Textbooks
- CIT-0023National Center for Complementary and Integrative Health. "Homeopathy: What You Need To Know." National Institutes of Health (2021).
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L0011Dr. Narayan Jethwani. "Thyroxine (T4 / FT4)." Homeo Healthcare Clinical Platform. Version 1.1.0. Reviewed: 2026-07-31T19:50:00Z. Available at: https://homeo.healthcare/knowledge/lab-tests/t4
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