Thyroxine.free

ChemistryAlso known as: T4 24h Ur-mRateAlso known as: T4 24h Ur-sRateAlso known as: T4 Bld Qlng/dL

Measures the level of active thyroid hormone (free T4) in your blood.

Normal Range

Consult your provider

ng/dL

Abnormal Levels

Consult your provider

Specimen Type

Blood

Why This Biomarker Matters

Free T4 directly reflects thyroid function. Abnormal levels cause metabolic problems, fatigue, weight changes, and mood disturbances requiring treatment.

Overview

Free T4, or thyroxine, is the active thyroid hormone that regulates metabolism, energy, and body temperature. This test measures the unbound form of T4 circulating in your blood—the portion your body can actually use. Low free T4 suggests an underactive thyroid (hypothyroidism), causing fatigue and weight gain. High free T4 indicates an overactive thyroid (hyperthyroidism), causing rapid heartbeat and anxiety. Free T4 is often ordered alongside TSH to assess thyroid function comprehensively.

Related Health Conditions

Conditions where Thyroxine.free is commonly tested

Hashimoto thyroiditis

Hyperthyroidism

Hypothyroidism

Thyroid nodule

Related Health Goals

Support Thyroid Health

Treatments & Interventions

Therapies monitored using Thyroxine.free

Thyroglobulin

Triiodothyronine

Sodium iodide

Sodium iodide (123-I)

Thyroxine

Levothyroxine sodium

Liothyronine sodium

Iopanoic acid

Kelp extract

Levothyroxine

Levothyroxine sodium anhydrous

Clinical Trials

Total Trials

Recruiting

With Results

Recent Trials

Natural History of Thyroid Function Disorders

NCT00001159Recruiting2,500 enrolled

Dosing of LT4 in Older Individuals

NCT06073665Phase 4Recruiting228 enrolled

Clinical and Basic Investigations Into Known and Suspected Congenital Disorders of Glycosylation

NCT02089789Recruiting200 enrolled

SNUH Immune Checkpoint Inhibitor-induced Hypothyroidism Recovery Trial

NCT07421869N/ARecruiting107 enrolled

Physical Activity, Fatigue, Social Support, and Psychological Well-Being in Women With Primary Hypothyroidism

NCT07408765Recruiting96 enrolled

View all 18 trials on ClinicalTrials.gov

Technical Information (LOINC Codes)

Standardized laboratory codes for this biomarker

3024-7Primary

Thyroxine (T4) free [Mass/volume] in Serum or Plasma

ng/dL

31144-9

Thyroxine (T4) [Mass/volume] in DBS

ug/dL

3026-2

Thyroxine (T4) [Mass/volume] in Serum or Plasma

ug/dL

38506-2

Thyroxine (T4) [Presence] in DBS

6892-4

Thyroxine (T4) free [Mass/volume] in Serum or Plasma by Dialysis

ng/dL

14921-1

Thyroxine (T4) [Moles/volume] in Serum or Plasma

nmol/L

27000-9

Thyroxine (T4) [Mass/volume] in Saliva (oral fluid)

ng/dL

53349-7

Thyroxine (T4) free [Mass/volume] in DBS

ng/dL

14920-3

Thyroxine (T4) free [Moles/volume] in Serum or Plasma

pmol/L

3025-4

Thyroxine (T4) [Mass/volume] in Blood

ug/mL

97166-3

Thyroxine (T4) [Mass/time] in 24 hour Urine

ug/(24.h)

97167-1

Thyroxine (T4) [Moles/time] in 24 hour Urine

mmol/(24.h)

98182-9

Thyroxine (T4) free [Moles/volume] in Cord blood

pmol/L

20451-1

Thyroxine (T4) [Presence] in Blood

31145-6

Thyroxine (T4) [Moles/volume] in DBS

pmol/L

53350-5

Thyroxine (T4) free [Moles/volume] in DBS

nmol/L

70217-5

Thyroxine (T4) free [Moles/volume] in Serum or Plasma by Dialysis

pmol/L

73557-1

Thyroxine (T4) free [Mass/volume] in Cord blood

ng/dL

83119-8

Thyroxine (T4) [Mass/volume] in Serum or Plasma by Immunoassay

ug/L

83120-6

Thyroxine (T4) [Moles/volume] in Serum or Plasma by Immunoassay

nmol/L

83121-4

Thyroxine (T4) free [Moles/volume] in Serum or Plasma by Immunoassay

pmol/L

83122-2

Thyroxine (T4) free [Mass/volume] in Serum or Plasma by Immunoassay

pg/mL

Available Lab Tests

Order tests that measure this biomarker

Free T4

$19.75

Results in 1-2 business days

T4 Free Direct Dialysis

$94.42

Find Specialists

Doctors who commonly order this test

Internal Medicine

Allergy & Immunology

Endocrinology, Diabetes & Metabolism