Differentiates aldosterone-producing adenoma from idiopathic adrenal hyperplasia based on 18-hydroxycorticosterone levels, with APA patients generally having levels >100 ng/dL at 8:00 a.m. and IAH patients usually having levels <100 ng/dL. Use when reviewing 18-OHB test results to help subtype PA; triggers include 18-OHB >100 ng/dL (suggesting APA) or <100 ng/dL (suggesting IAH).
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---
name: esa-pa-interpret-18ohb
description: Differentiates aldosterone-producing adenoma from idiopathic adrenal hyperplasia based on 18-hydroxycorticosterone levels, with APA patients generally having levels >100 ng/dL at 8:00 a.m. and IAH patients usually having levels <100 ng/dL. Use when reviewing 18-OHB test results to help subtype PA; triggers include 18-OHB >100 ng/dL (suggesting APA) or <100 ng/dL (suggesting IAH).
---
# Interpret 18-Hydroxycorticosterone Levels for PA Subtyping
## STEP 1 — Gather Information
Collect patient's 8:00 a.m. seated plasma 18-hydroxycorticosterone (18-OHB) level, along with confirmatory PA diagnosis (positive ARR and confirmatory test), and note any medications that could affect steroid synthesis (e.g., MR antagonists) that should be withdrawn for at least 4 weeks prior to testing.
## STEP 2 — Rule In / Rule Out
Rule out spurious low 18-OHB due to recent MR antagonist use or sample handling issues; if 18-OHB is measurable and patient is off interfering drugs, proceed to interpretation.
## STEP 3 — Classify or Stratify
If 18-OHB >100 ng/dL at 8:00 a.m., classify as suggestive of aldosterone-producing adenoma (APA); if 18-OHB <100 ng/dL, classify as suggestive of idiopathic adrenal hyperplasia (IAH); borderline values (90-110 ng/dL) require integration with imaging and AVS.
## STEP 4 — Decide
For values >100 ng/dL, prioritize AVS to confirm unilateral disease and consider laparoscopic adrenalectomy; for values <100 ng/dL, plan for medical therapy with MR antagonist and consider AVS only if surgical candidacy is uncertain.
## Clinical Guardrails / Mimics / Pitfalls
Do not rely solely on 18-OHB for subtype diagnosis; avoid testing while on MR antagonists or potassium-wasting diuretics which can falsely lower 18-OHB; remember that IAH may occasionally show elevated 18-OHB and APA may rarely fall below cutoff, so correlate with CT and AVS.
## Concrete Clinical Example
A 52-year-old hypertensive patient with confirmed PA has an 8:00 a.m. 18-OHB of 132 ng/dL after 6 weeks off spironolactone; this exceeds the 100 ng/dL threshold, prompting AVS which shows lateralization consistent with APA, leading to laparoscopic adrenalectomy.
**Source:** The Management of Primary Aldosteronism: Case Detection, Diagnosis, and Treatment: An Endocrine Society Clinical Practice Guideline, Endocrine Society, 2016, DOI: 10.1210/jc.2015-4061
