Thyroid-Stimulating Hormone (TSH)
The most likely increased laboratory value in this patient is thyroid-stimulating hormone (TSH), as she presents with the classic constellation of hypothyroidism: weight gain, constipation, dry cool skin, periorbital edema, bradycardia, and hypertension. 1
Clinical Reasoning
This patient's presentation is textbook for hypothyroidism, which the ACC/AHA guidelines specifically identify with the following features that match this case exactly 1:
- Symptoms: Dry skin, cold intolerance (implied by cool skin), constipation, weight gain, and generalized weakness 1
- Physical examination findings: Periorbital puffiness, coarse/dry skin, cold skin, and delayed ankle reflex 1
- Cardiovascular manifestations: Bradycardia (HR 59 bpm) and hypertension (BP 160/100 mmHg) are both associated with hypothyroidism 1
The ACC/AHA guidelines explicitly state that the screening test for hypothyroidism is TSH with free thyroxine, and in primary hypothyroidism (which accounts for over 99% of cases), TSH is elevated while T4 is low 1, 2.
Why the Other Options Are Incorrect
Cortisol would be elevated in Cushing's syndrome, but this diagnosis is inconsistent with the clinical picture 1:
- Cushing's presents with rapid weight gain with central distribution, proximal muscle weakness, depression, and hyperglycemia 1
- Physical findings include central obesity, "moon face," dorsal and supraclavicular fat pads, and wide violaceous striae 1
- This patient lacks these characteristic features and instead has the cool, dry skin of hypothyroidism rather than the warm, moist skin that would be expected with other endocrine disorders 1
Potassium would not be elevated in hypothyroidism 1. Hypokalemia is associated with conditions like primary aldosteronism, Cushing's syndrome, and congenital adrenal hyperplasia, none of which fit this presentation 1.
Total iron-binding capacity (TIBC) is elevated in iron deficiency anemia, which does not explain this patient's constellation of symptoms 1. While fatigue could occur with anemia, the bradycardia, hypertension, periorbital edema, and cool dry skin point definitively toward hypothyroidism 1.
Critical Clinical Pearls
The periorbital edema in this case is particularly telling, as it results from increased capillary permeability to protein and fluid retention that occurs even in mild hypothyroidism 3, 4, 5. This edema can be associated with excessive diurnal weight gain and responds to thyroid hormone replacement 5.
The leg cramps mentioned in the history are also consistent with hypothyroidism and may relate to the metabolic derangements and delayed muscle relaxation that occur with thyroid hormone deficiency 1.
The hypertension in hypothyroidism occurs in less than 1% of cases but is a recognized association, making this an important secondary cause to screen for in young patients with new-onset hypertension 1.