T-Uptake

CPT Code(s):
84479

Turnaround Time:
8 hours

Specimen Requirements

Preferred Specimen:
Serum

Minimum Volume:
1.0 mL

Transport Container:
Serum Separator Tube (SST)

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:
Quantity not sufficient for analysis; improper specimen (serum, plasma, blood); incomplete specimen identification

Stability Criteria

Room Temperature:
8 hours

Refrigerated:
7 days

Frozen:
30 days

Clinical Significance

The T3 Uptake (Thyroxine Binding Capacity) test has specific clinical significance and diagnostic use in assessing the binding capacity of thyroxine (T4)-binding proteins in the blood. Here are key points regarding its clinical significance:

1. Evaluation of Thyroid Function: T3 Uptake provides indirect information about thyroid hormone levels and function. It helps assess the binding capacity of proteins, such as thyroxine-binding globulin (TBG), transthyretin (previously known as thyroxine-binding prealbumin), and albumin, which transport thyroid hormones in the blood.

2. Differential Diagnosis of Thyroid Disorders: The test aids in the differential diagnosis of thyroid disorders, particularly when used in conjunction with other thyroid function tests such as T3, T4, and thyroid-stimulating hormone (TSH) levels. Abnormal T3 Uptake results can provide insights into the underlying cause of thyroid dysfunction, including conditions such as hyperthyroidism and hypothyroidism.

3. Assessment of Thyroid Hormone Binding Proteins: T3 Uptake indirectly reflects the availability and activity of thyroxine-binding proteins in the blood. Changes in protein levels or binding capacity can impact the transport and distribution of thyroid hormones, affecting overall thyroid function.

4. Monitoring of Thyroid Hormone Replacement Therapy: T3 Uptake can be useful in monitoring patients receiving thyroid hormone replacement therapy. It helps healthcare providers evaluate the binding capacity of proteins and assess the adequacy of treatment.

5. Evaluation of Non-Thyroidal Illness: Abnormal T3 Uptake results may occur in non-thyroidal illness, such as systemic illnesses or certain medications, indicating alterations in the binding capacity of thyroid hormone-binding proteins.

It is important to note that T3 Uptake is an indirect measurement and does not directly assess thyroid hormone levels. It provides valuable information about thyroid hormone transport and binding capacity in the blood, assisting healthcare providers in the evaluation and management of thyroid disorders. The test is often used in conjunction with other thyroid function tests to obtain a comprehensive assessment of thyroid status.