A 25-year-old woman presents with amenorrhoea for 8 months, galactorrhoea, and headaches. A pregnancy test is negative. What is the most appropriate investigation? A) Pelvic ultrasound B) Serum prolactin C) FSH and LH D) MRI brain E) Thyroid function tests Correct Answer: B) Serum prolactin Explanation: This woman has hyperprolactinaemia, which can cause amenorrhoea and galactorrhoea. The first-line test is serum prolactin. If elevated, an MRI of the pituitary is needed to rule out a prolactinoma. A) Pelvic ultrasound → Incorrect. Useful for PCOS, but not first-line here. C) FSH and LH → Incorrect. Used for primary ovarian insufficiency, but hyperprolactinaemia is more likely. D) MRI brain → Incorrect. Only done if prolactin is persistently elevated. E) Thyroid function tests → Incorrect. Hypothyroidism can cause mild hyperprolactinaemia, but a direct prolactin level is the first step. Key Tips for PLAB 1: ✅ Amenorrhoea + galactorrhoea → Suspect hyperprolactinaemia. ✅ First-line test = Serum prolactin. ✅ If prolactin is high → MRI brain to rule out prolactinoma.
