SMLEREVISE

Primary Hypothyroidism: Diagnosis and Management

Medically Reviewed by Dr. M. Salar Raza | Official SCFHS 2026 Blueprint

Clinical Pathway

Primary hypothyroidism is characterized by an underactive thyroid gland, resulting in decreased production of thyroid hormones. Common symptoms include fatigue, weight gain, cold intolerance, constipation, and dry skin. The diagnosis is established by finding an elevated Thyroid Stimulating Hormone (TSH) and a low free Thyroxine (Free T4). The standard treatment is daily replacement therapy with synthetic levothyroxine (T4). The goal of therapy is to normalize the serum TSH level, which should be rechecked 6-8 weeks after initiating or adjusting the dose.

Clinical Reasoning

In primary hypothyroidism, the failing thyroid gland produces less T4. Through the negative feedback loop, the pituitary gland responds to the low T4 by increasing the secretion of TSH to stimulate the thyroid. Therefore, an elevated TSH and a low Free T4 confirm the diagnosis of primary hypothyroidism. Hashimoto's thyroiditis is the most common cause. Treatment with levothyroxine aims to restore euthyroidism and relieve symptoms. TSH is the most sensitive marker to monitor the adequacy of levothyroxine replacement.

Sample MCQ

A 55-year-old woman complains of fatigue, a 10-pound weight gain over the last few months, and feeling cold all the time. On examination, her skin is dry, and her deep tendon reflexes exhibit a delayed relaxation phase. Which of the following laboratory profiles is most consistent with her likely diagnosis?

  • ALow TSH, High Free T4
  • BHigh TSH, Low Free T4
  • CLow TSH, Low Free T4
  • DHigh TSH, High Free T4

Correct Answer: High TSH, Low Free T4

The patient's symptoms of fatigue, weight gain, cold intolerance, dry skin, and delayed relaxation of deep tendon reflexes are classic signs of hypothyroidism. In primary hypothyroidism (the most common type), the thyroid gland fails to produce enough thyroid hormones (low Free T4). This loss of negative feedback causes the pituitary gland to increase the production of Thyroid Stimulating Hormone (high TSH).

Master the 2026 SMLE

Explore more clinical protocols in the SMLEREVISE Clinical Knowledge Library.

Try the QBank & Scaled Mocks