From the Guidelines
For a patient with elevated TSH levels, additional laboratory tests should include free T4 (thyroxine), free T3 (triiodothyronine), and thyroid antibodies such as thyroid peroxidase antibodies (TPOAb) and thyroglobulin antibodies (TgAb). These tests are essential to distinguish between subclinical hypothyroidism and overt hypothyroidism, and to identify autoimmune thyroid disease, which is the most common cause of hypothyroidism in iodine-sufficient regions 1.
Key Laboratory Tests
- Free T4 (thyroxine) to distinguish between subclinical and overt hypothyroidism
- Free T3 (triiodothyronine) to assess peripheral thyroid hormone conversion
- Thyroid antibodies (TPOAb and TgAb) to identify autoimmune thyroid disease
Additional Tests
In certain cases, especially when thyroid nodules are present or malignancy is suspected, ultrasound imaging of the thyroid gland may be warranted. For patients with severe symptoms or very high TSH levels, lipid profile and complete blood count may be useful to assess metabolic effects of hypothyroidism. These tests collectively provide a comprehensive evaluation of thyroid function and help determine the underlying cause of the elevated TSH, which is crucial for appropriate management and treatment planning 1.
Clinical Considerations
The most common cause of hypothyroidism in the United States is chronic autoimmune (Hashimoto) thyroiditis, and risk factors for an elevated TSH level include female sex, advancing age, white race, type 1 diabetes, Down syndrome, family history of thyroid disease, goiter, previous hyperthyroidism, and external-beam radiation in the head and neck area 1.
Treatment
The principal treatment for hypothyroidism is oral T4 monotherapy (levothyroxine sodium), and hyperthyroidism is treated with antithyroid medications or nonreversible thyroid ablation therapy 1.
From the Research
Additional Labs for Elevated TSH
For a patient with an elevated Thyroid-Stimulating Hormone (TSH) level of 38, the following additional labs may be ordered:
- Free T4 (FT4) and Free T3 (FT3) to assess the levels of these hormones in the blood, as TSH levels can be elevated even when FT4 and FT3 levels are normal 2
- Thyroid peroxidase antibodies (TPO) and anti-thyroglobulin antibodies (TGA) to check for autoimmune thyroiditis, a common cause of hypothyroidism 3
- Complete blood cell count (CBC) with differential and complete metabolic profile (CMP) to rule out other underlying conditions that may be contributing to the elevated TSH level 3
- High-sensitivity C-reactive protein (hs-CRP) to assess inflammation, which may be associated with hypothyroidism 3
Rationale for Lab Orders
The rationale for ordering these labs is to:
- Confirm the diagnosis of hypothyroidism and assess its severity
- Identify potential underlying causes of hypothyroidism, such as autoimmune thyroiditis
- Rule out other conditions that may be contributing to the elevated TSH level
- Monitor the patient's response to treatment and adjust the treatment plan as needed
Limitations of T3 Testing
It is worth noting that T3 testing may not be necessary in all cases of elevated TSH, as T3 levels can be normal even in patients with hypothyroidism 4. Additionally, T3 levels can be affected by various factors, such as non-thyroidal illness and certain medications 5. Therefore, T3 testing should be ordered judiciously and in conjunction with other lab tests and clinical evaluation.