A pattern with Na 148, K 2.9, Cl 108, serum osmolality 300; Urine K 60, Cl 20, Na 148, urine osmolality 650. This pattern is most consistent with which condition?

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The pattern tests how excess mineralocorticoid (aldosterone) activity affects electrolytes and urine. When aldosterone is inappropriately high, the kidneys increase reabsorption of sodium and increase excretion of potassium and hydrogen ions in the collecting ducts. This produces hypertension and a low serum potassium (hypokalemia), with a tendency for the serum sodium to be normal or slightly elevated due to sodium retention.

In the data, the potassium is notably low (2.9), which strongly points to excessive aldosterone driving potassium loss. The serum sodium is high-normal (Na 148), which can occur with aldosterone-driven sodium retention and volume expansion. The urine shows a high potassium excretion (urine K 60), which directly reflects the aldosterone effect on the distal nephron. The urine is also quite concentrated (urine osmolality 650), consistent with active renal handling of solutes and water in this setting.

The other conditions don’t fit as well. SIADH causes hyponatremia with low serum osmolality and inappropriately concentrated urine, not a hypernatremic, hypokalemic pattern. Addison’s disease would typically raise serum potassium (hyperkalemia) and lower serum sodium, along with hypotension. Hypoaldosteronism also leads to hyperkalemia and hyponatremia rather than the observed hypokalemia and hypernatremia.

So the combination of hypokalemia with high urinary potassium, plus a tendency toward higher serum sodium, aligns best with Conn’s disease, hyperaldosteronism.