Thyroid Test Interpretation

The patient presents with generalized weakness and the following thyroid function test (TFT) results:

• Serum $T_3$ = Normal
• Serum $T_4$ = Normal
• TSH = $10 \text{mU/L}$ (Elevated)

Diagnosis Justification

The key findings are normal levels of the active thyroid hormones ($T_3$ and $T_4$) despite an elevated Thyroid Stimulating Hormone ($\text{TSH}$) level.

• Subclinical Hypothyroidism: This condition is characterized by elevated $\text{TSH}$ levels with normal circulating thyroid hormones ($T_3$ and $T_4$). The pituitary gland releases more $\text{TSH}$ in an attempt to stimulate a thyroid gland that is beginning to fail, but the gland can still produce sufficient hormones initially. This pattern matches the patient's results.
• Primary Hypothyroidism: This would typically show elevated $\text{TSH}$ along with low $T_3$ and $T_4$ levels.
• Secondary Hypothyroidism: This arises from a problem with the pituitary gland, leading to low or inappropriately normal $\text{TSH}$ levels, along with low $T_3$ and $T_4$.
• Non-Thyroidal Illness (Euthyroid Sick Syndrome): This occurs in severe illness and usually involves low $T_3$ and $T_4$ levels, with variable $\text{TSH}$ (often low or normal).

Based on the provided results (Normal $T_3$, Normal $T_4$, and Elevated $\text{TSH}$), subclinical hypothyroidism is the most likely diagnosis.