Triiodothyronine, Total (Total T3)
CPT Code(s):
84480
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:
8 days
Refrigerated:
14 days
Frozen:
183 days
Clinical Significance
T3 is a diagnostic tool used to measure the levels of triiodothyronine (T3) in a patient's blood. T3 is one of the two main thyroid hormones produced by the thyroid gland and plays a crucial role in regulating metabolism, growth, and development. T3 has specific clinical significance and diagnostic use in the following ways:
1. Evaluation of Thyroid Function: T3 is used to assess thyroid function and diagnose thyroid disorders. It is often performed in conjunction with other thyroid hormone tests, such as T4 and thyroid-stimulating hormone (TSH) test. Abnormal T3 levels can indicate an overactive thyroid (hyperthyroidism) or an underactive thyroid (hypothyroidism).
2. Monitoring Thyroid Treatment: Patients with thyroid disorders, such as hyperthyroidism or hypothyroidism, may undergo T3 testing to monitor the effectiveness of their thyroid treatment. T3 levels can help healthcare providers adjust medication dosage and ensure optimal management of the thyroid condition.
3. Differential Diagnosis: T3 is used in combination with other thyroid tests to differentiate between different types of thyroid disorders. For example, in cases of suspected hyperthyroidism, elevated T3 levels in the presence of normal or low T4 levels can suggest a condition known as T3 toxicosis.
4. Investigation of Non-Thyroidal Illness: T3 levels may be altered in certain non-thyroidal illnesses, such as critical illness or severe systemic illness. T3 can help identify these alterations and aid in the investigation and management of the underlying condition.
5. Monitoring Athletes: T3 levels may be monitored in athletes, particularly those involved in sports that require weight control, as changes in T3 levels can be associated with alterations in metabolism and energy balance.
6. Thyroid Hormone Resistance Syndromes: In rare cases, individuals may exhibit resistance to the effects of thyroid hormones due to genetic mutations. Measuring T3 levels can help in the diagnosis and management of these thyroid hormone resistance syndromes.
In summary, T3 is used to assess thyroid function, diagnose thyroid disorders, monitor thyroid treatment, and investigate non-thyroidal illnesses. It provides valuable information for healthcare providers to make accurate diagnoses and develop appropriate treatment plans for patients with thyroid-related conditions. Interpretation of T3 results is often done in conjunction with other thyroid function tests to gain a comprehensive understanding of the patient's thyroid status.