What is the single most likely electrolyte pattern to be found in a patient with tiredness, permanent skin tanning, and dizziness upon standing?

The symptoms described—tiredness, permanent skin tanning, and dizziness upon standing—are highly suggestive of adrenal insufficiency, particularly primary adrenal insufficiency (Addison's disease). In this condition, the adrenal glands do not produce enough steroid hormones, including cortisol and aldosterone.

One of the significant electrolyte imbalances seen in primary adrenal insufficiency is hyponatremia (low sodium) and hyperkalemia (high potassium). The elevated potassium level is due to the decreased secretion of aldosterone, which normally promotes the excretion of potassium. Low sodium levels occur due to the loss of aldosterone, which also promotes sodium retention.

The first option presents an electrolyte pattern of sodium at 120 mmol/L, which indicates severe hyponatremia, and potassium at 5.9 mmol/L, which suggests hyperkalemia. This change aligns perfectly with the clinical profile of a patient suffering from Addison's disease, presenting with symptoms of tiredness and dizziness due to reduced blood volume and low sodium levels leading to hypotension, particularly when standing (orthostatic hypotension).

The other options do not correlate with the typical electrolyte disturbances associated with adrenal insufficiency—such as the normalized sodium and potassium levels in the other choices