Triiodothyronine, Free (Free FT3)
CPT Code(s):
84481
Turnaround Time:
4 hours
Specimen Requirements
Preferred Specimen:
Serum
Minimum Volume:
1.0 mL
Transport Container:
Serum Separator Tube (SST) or Red Top Tube
Transport Temperature:
Room Temperature
Collection Instructions:
Allow blood to clot completely prior to centrifugation. Separate serum from cells within 45 minutes of collection.
Rejection Criteria:
Plasma specimen; gross hemolysis; lipemia; improper labeling
Stability Criteria
Room Temperature:
5 days
Refrigerated:
7 days
Frozen:
30 days
Clinical Significance
Free T3 holds specific clinical significance and diagnostic use in assessing thyroid function and diagnosing thyroid disorders. Triiodothyronine (T3) is a thyroid hormone that plays a vital role in regulating metabolism, growth, and development in the body. Free T3 measures the amount of unbound or active T3 in the blood, providing important information about thyroid function.
The specific clinical significance and diagnostic use of Free T3 include:
1. Assessment of Thyroid Function: Free T3 is used to evaluate thyroid function and assess the production and activity of T3 hormone. It helps differentiate between primary, secondary, and tertiary hypothyroidism and hyperthyroidism, providing insights into the underlying cause of thyroid dysfunction. Abnormal Free T3 levels, along with other thyroid function tests, aid in diagnosing and monitoring thyroid disorders.
2. Diagnosis of Hyperthyroidism: Hyperthyroidism, characterized by excessive thyroid hormone production, can lead to a wide range of symptoms such as weight loss, tremors, rapid heart rate, and heat intolerance. Free T3 plays a key role in diagnosing hyperthyroidism, as elevated levels of Free T3 indicate increased thyroid hormone activity. It helps healthcare providers assess the severity of hyperthyroidism and guide appropriate treatment strategies.
3. Monitoring Thyroid Replacement Therapy: Free T3 is used to monitor the effectiveness of thyroid hormone replacement therapy in individuals with hypothyroidism. Hypothyroidism occurs when the thyroid gland does not produce enough thyroid hormones, resulting in symptoms such as fatigue, weight gain, and cold intolerance. Regular monitoring of Free T3 levels helps ensure that thyroid hormone replacement therapy is within the therapeutic range, optimizing treatment outcomes and maintaining normal thyroid function.
4. Evaluation of Thyroid Dysfunction in Pregnancy: Free T3 is particularly useful in monitoring thyroid function during pregnancy. Thyroid hormone imbalances during pregnancy can impact the health of both the mother and the developing fetus. Measuring Free T3 levels aids in the diagnosis and management of thyroid disorders in pregnant women, helping to ensure appropriate thyroid hormone levels for optimal maternal and fetal well-being.
5. Assessment of Thyroid Function in Critical Illness: Free T3 is used in the evaluation of thyroid function in critically ill patients. Critical illness can affect thyroid hormone metabolism, resulting in altered Free T3 levels. Monitoring Free T3 levels helps healthcare providers assess thyroid function and guide appropriate interventions in critically ill individuals.
It is important to note that the interpretation of Free T3 levels requires consideration of other thyroid function tests, such as Free T4 and thyroid-stimulating hormone (TSH), as well as clinical presentation and patient history. Combining these results provides a more comprehensive assessment of thyroid function.
In summary, Free T3 has specific clinical significance in assessing thyroid function, diagnosing hyperthyroidism, monitoring thyroid replacement therapy, evaluating thyroid dysfunction in pregnancy, and assessing thyroid function in critical illness. By measuring Free T3 levels in a patient's blood, this test provides valuable information for clinical decision-making, diagnosing and managing thyroid disorders, and optimizing patient care outcomes related to thyroid health.