A female patient with hypertension has a serum potassium level of 2.7mmol/l. Which hormone would you be looking for?

In a female patient with hypertension and a significantly low serum potassium level of 2.7 mmol/L, the hormone of interest is aldosterone. Aldosterone is a mineralocorticoid hormone produced by the adrenal cortex that plays a key role in regulating sodium and potassium levels in the body. It promotes sodium reabsorption and potassium excretion in the kidneys.

In conditions such as primary hyperaldosteronism (often referred to as Conn's syndrome), excessive production of aldosterone leads to the retention of sodium, resulting in hypertension, and increased excretion of potassium, which can result in hypokalemia, as seen in this patient. Evaluating aldosterone levels can help in diagnosing such endocrine disorders especially when hypertension is present alongside hypokalemia.

The other hormones listed do not directly relate to the condition described. Cortisol, while it can have effects on blood pressure and electrolytes, does not typically cause such low levels of potassium when its regulation is functioning normally. Thyrotoxin (thyroid hormones), while they may influence various metabolic processes, are not directly associated with managing potassium levels in the setting of hypertension. Lastly, renin would be evaluated in cases of suspected renal causes of hypertension, but the hypokalemia strongly points towards