Reading the Workup for Adrenal Insufficiency

Adrenal insufficiency means the body cannot make enough cortisol, and the workup has to answer two questions: is cortisol truly deficient, and is the problem in the adrenal gland or in the pituitary that commands it. A morning cortisol paired with ACTH screens for the deficiency and its location, while a short cosyntropin stimulation test serves as the confirmatory standard. Because the symptoms are vague and a crisis can be dangerous, the reasoning behind these tests is worth understanding.

What is failing, and where

Cortisol is produced by the adrenal cortex under the command of ACTH, a hormone released by the pituitary. Adrenal insufficiency can arise at either level. In primary adrenal insufficiency, historically called Addison disease, the adrenal glands themselves fail. In secondary insufficiency, the pituitary does not send enough ACTH, often because of pituitary disease or suppression from external glucocorticoid or opioid medication.

That two-level structure shapes the whole evaluation. Confirming low cortisol is only half the task. The other half is locating the failure, because the pattern of hormones and the associated features differ between the two.

Symptoms that hide the diagnosis

The clinical picture is notoriously nonspecific. Unintentional weight loss, poor appetite, profound fatigue, muscle and abdominal pain, and low blood pressure on standing are common, and a low blood sodium can appear on routine labs. As the Lancet review notes, this vagueness is exactly why diagnosis is frequently delayed.

Primary disease often adds distinctive clues. Because the failing adrenal also underproduces aldosterone, salt craving and high potassium can appear, and the high ACTH that accompanies primary failure can darken the skin. These features help point toward the primary form before any test is ordered.

The screening pair: morning cortisol and ACTH

Cortisol follows a daily rhythm and peaks in the early morning, so an 8 a.m. sample is the informative one. A very low morning cortisol strongly raises suspicion of insufficiency, while a robustly high value makes it unlikely. Values in between are common and do not settle the question on their own.

Measuring ACTH at the same time localizes the problem. A high ACTH alongside low cortisol indicates the pituitary is shouting at an adrenal that cannot answer, the signature of primary disease. A low or inappropriately normal ACTH with low cortisol points instead to the pituitary as the source. The Endocrine Society guideline frames this paired measurement as the initial screening step when the definitive test cannot be done immediately.

The confirmatory standard

The short cosyntropin stimulation test is the reference the guideline calls the standard. A synthetic fragment of ACTH is given, and cortisol is measured before and after to see whether the adrenal can mount a normal rise. A peak that fails to reach the expected threshold confirms insufficiency.

One nuance a careful reader should hold is that the cortisol cutoff is not universal. Different laboratory assays calibrate differently, so the threshold that defines a normal response depends on the method used. This is a reminder that endocrine testing, like glucose testing, is only as trustworthy as the assay behind the number.

Finding the cause, and why urgency matters

Once primary insufficiency is confirmed, the workup turns to why the adrenal failed. In much of the world the leading cause is autoimmune destruction, and a validated assay for 21-hydroxylase autoantibodies supports that diagnosis. When antibodies are absent, other causes are pursued.

The reason all of this reasoning is worth knowing is safety. Untreated adrenal insufficiency can progress to an adrenal crisis, a medical emergency. This article explains how clinicians and guidelines read the workup, as education about diagnostic logic. It is not dosing guidance or personal medical advice, and anyone with these symptoms needs evaluation by a clinician who can order and interpret the tests directly.