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Difficulty: HardInterpreting Laboratory Results

Match each constellation of endocrinologic laboratory findings to the most likely diagnostic etiology in young adult patients presenting with resistant hypertension and unprovoked hypokalemia.

  • Elevated plasma aldosterone, suppressed plasma renin activity, PAC/PRA ratio >20> 20Aldosterone-producing adenoma
  • Elevated plasma aldosterone, elevated plasma renin activity, PAC/PRA ratio <10< 10Renovascular hypertension
  • Suppressed plasma aldosterone, suppressed plasma renin activity, minimal blood pressure response to spironolactone, responsive to amilorideLiddle syndrome
  • Suppressed plasma aldosterone, suppressed plasma renin activity, markedly elevated urinary free cortisol-to-cortisone ratioSyndrome of apparent mineralocorticoid excess
  • Suppressed plasma aldosterone, suppressed plasma renin activity, elevated serum 1111-deoxycorticosterone, low serum DHEA-S17α17\alpha-hydroxylase deficiency

Answer

The laboratory profiles correctly map to their etiologies based on the state of the renin-angiotensin-aldosterone system (RAAS) and specific markers of adrenal steroidogenesis.
Each laboratory profile distinctly reflects a specific pathophysiological derangement in the RAAS axis or adrenal steroidogenesis that perfectly corresponds to its respective etiology.

Step-by-Step Solution

1
Evaluate the plasma aldosterone concentration (PAC) and plasma renin activity (PRA) to categorize the hypertension into primary hyperaldosteronism, secondary hyperaldosteronism, or a non-aldosterone mineralocorticoid excess state.
Elevated PAC and PRA indicates secondary hyperaldosteronism; elevated PAC and low PRA indicates primary hyperaldosteronism; low PAC and low PRA indicates another mineralocorticoid source or an ENaC defect.
The RAAS axis dynamically responds to volume status and primary driver mutations, making it the essential first step in differentiating these etiologies.
2
For profiles with both suppressed PAC and PRA, analyze the additional metabolic and steroidogenic clues, such as the cortisol-to-cortisone ratio, 1111-deoxycorticosterone levels, or specific medication responses.
An elevated cortisol-to-cortisone ratio identifies 11β11\beta-HSD2 deficiency, elevated 1111-deoxycorticosterone with low androgens points to 17α17\alpha-hydroxylase deficiency, and an isolated ENaC defect identifies Liddle syndrome.
Because aldosterone is appropriately suppressed by the hypervolemic state, identifying the alternate mechanism of sodium retention is required to finalize the diagnosis.

Key Concept

Interpretation of the renin-angiotensin-aldosterone system (RAAS) and steroidogenic pathway laboratories in the differential diagnosis of mineralocorticoid hypertension and hypokalemia.

Alternative Method

A systematic algorithmic approach to laboratory evaluation involves calculating the PAC/PRA ratio first: if >20> 20, suspect primary aldosteronism; if <10< 10 with high renin, suspect a secondary cause; if both are suppressed, systematically measure serum 1111-deoxycorticosterone and the urinary free cortisol-to-cortisone ratio.
Estimated Time:2m 30s
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Interpreting Laboratory Results

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