Reading the Workup for Adrenal Insufficiency

The adrenal insufficiency workup is not a hunt for one universal cortisol cutoff. It combines clinical urgency, test timing, medication history, the laboratory assay, and the distinction between primary adrenal failure and inadequate signaling from the pituitary or hypothalamus. That distinction matters because mineralocorticoid deficiency is typical of primary disease but not central disease, causes differ, and an adrenal crisis cannot wait for a perfect outpatient test sequence.

Key points#

• Severe illness with suspected adrenal crisis requires immediate treatment; testing must not delay it.
• An early-morning cortisol is an initial probability test, not a stand-alone answer in every setting.
• Paired ACTH helps distinguish primary from central adrenal insufficiency once cortisol deficiency is established.
• A standard 250 microgram corticotropin stimulation test assesses adrenal response, with assay-specific interpretation.
• Exogenous glucocorticoids, binding-protein changes, recent pituitary injury, and critical illness can distort results.

Recognize the emergency pathway first#

Adrenal crisis can present with hypotension, volume depletion, vomiting, abdominal pain, weakness, fever, confusion, hypoglycemia, or electrolyte abnormalities, and primary adrenal insufficiency may produce hyponatremia and hyperkalemia because aldosterone is also deficient. Central disease can cause hyponatremia, but aldosterone is usually preserved.

No single feature is specific. Sepsis, gastrointestinal illness, medication effects, and other endocrine disorders can look similar. The safety rule is therefore based on consequence: when a person is severely ill and adrenal crisis is reasonably suspected, guidelines recommend drawing cortisol and ACTH if that can be done promptly, then giving stress-dose hydrocortisone and fluids without waiting for results. Treatment changes later testing, but delaying treatment can be dangerous. A pre-treatment sample is valuable only when obtaining it does not slow resuscitation.

Map the hormonal pathway#

The hypothalamus releases corticotropin-releasing hormone, prompting the pituitary to release adrenocorticotropic hormone, or ACTH. ACTH stimulates the adrenal cortex to produce cortisol. Primary adrenal insufficiency means the adrenal glands cannot respond adequately, so cortisol is low and ACTH typically rises; secondary or tertiary disease means ACTH drive is insufficient because of pituitary or hypothalamic dysfunction, including suppression after glucocorticoid treatment. Cortisol is low while ACTH is low or inappropriately normal.

Primary disease can also reduce aldosterone, raising renin and contributing to salt loss, low blood pressure, and hyperkalemia. ACTH-related peptides can cause hyperpigmentation. Central disease may occur with other pituitary hormone deficits, headache, visual symptoms, pituitary surgery, radiation, or a mass. None of these clues replaces biochemical confirmation, but they set the pretest probability you start from and guide the cause evaluation.

Medication history is essential. Oral, injected, inhaled, topical, and intra-articular glucocorticoids can suppress the axis depending on dose, duration, absorption, and individual susceptibility. Opioids, immune checkpoint inhibitors, and medicines that alter cortisol synthesis or metabolism can also matter. A drug recorded as “not oral” should not be assumed irrelevant.

Use morning cortisol as a probability update#

Cortisol normally peaks in the early morning. Testing around 8 to 9 AM makes interpretation more standardized than a random level: very low values strongly raise concern, and clearly high values can make adrenal insufficiency unlikely in stable outpatients. Intermediate results require dynamic testing or specialist interpretation.

Older Endocrine Society guidance cited a morning cortisol below 5 micrograms/dL with ACTH as a preliminary indicator of primary adrenal insufficiency when stimulation testing was unavailable. For central disease, its hypopituitarism guideline described below 3 micrograms/dL as strongly suggestive and above 15 micrograms/dL as making the diagnosis unlikely. These are not universal laboratory boundaries. Modern cortisol assays can read lower than older immunoassays, and laboratories should validate method-specific thresholds.

NICE's 2024 guideline uses its own referral bands and emphasizes timing, context, and local assays; the apparent disagreement between cutoffs often reflects different purposes: screening, ruling in, ruling out, or deciding who needs specialist testing. Interpret the value you are holding against the guideline and the assay that threshold was derived for.

Total serum cortisol also depends on cortisol-binding globulin and albumin. Estrogen therapy and pregnancy can raise binding proteins and total cortisol, while cirrhosis, nephrotic syndrome, and critical illness can lower them, and the biologically active free fraction may not move in parallel with the reported total value.

Pair cortisol with ACTH when possible#

ACTH should be drawn at the same time as the baseline cortisol, before glucocorticoid treatment when circumstances allow. The sample needs correct handling because ACTH is unstable. In confirmed cortisol deficiency, an ACTH more than twice the upper reference limit supports primary adrenal insufficiency. Low or inappropriately normal ACTH points toward central disease.

ACTH alone does not establish adequate cortisol reserve. Early primary disease can be evolving, and recent central injury can leave the adrenal glands temporarily responsive even when pituitary signaling has failed. Interpretation depends on both hormones, clinical timing, and other pituitary or adrenal findings.

If primary disease is confirmed, plasma renin and aldosterone help assess mineralocorticoid deficiency. Sodium and potassium provide clues but are not sufficiently sensitive or specific to establish the diagnosis.

Understand what the stimulation test asks#

The standard corticotropin test measures cortisol before and 30 or 60 minutes after 250 micrograms of synthetic ACTH, also called cosyntropin or tetracosactide, and an adequate rise indicates that the adrenal cortex can respond to a strong signal. A subnormal peak supports adrenal insufficiency.

The traditional peak threshold near 18 micrograms/dL, or 500 nmol/L, came from older assays. More specific monoclonal immunoassays and liquid chromatography methods often require lower validated cutoffs. Using an old threshold with a newer assay can create false diagnoses. The report has to say which assay was used and what the laboratory's validated decision limit is.

The standard test performs well for established primary adrenal insufficiency. It can miss recent central disease because adrenal atrophy takes time after ACTH drive falls, and insulin tolerance testing or metyrapone testing may be considered in specialist settings when central disease remains strongly suspected, but each has contraindications and operational demands.

The 1 microgram low-dose ACTH test has been proposed as more sensitive for central disease, though it is technically vulnerable to dilution and dosing errors and is not the routine primary-disease test in Endocrine Society guidance. A local protocol and experienced laboratory matter.

Limits and common testing traps#

Glucocorticoids can suppress endogenous cortisol and some can cross-react with cortisol assays. Testing must be timed around the specific agent under clinical direction. Dexamethasone has little cross-reactivity in many assays but still changes physiology, and hydrocortisone is cortisol, so it affects the measurement directly.

Acute illness raises expected cortisol, so a seemingly ordinary value can be inappropriate for the degree of stress. Critical-illness-related corticosteroid physiology is also not identical to stable outpatient adrenal insufficiency, and consensus thresholds have limitations.

Biotin can interfere with some immunoassays. Shift work disrupts ordinary circadian timing, and pregnancy changes binding proteins and reference ranges. Recent pituitary surgery, hemorrhage, traumatic injury, or checkpoint-inhibitor therapy changes both urgency and the reliability of standard sequences.

Find the cause only after securing the diagnosis#

For primary adrenal insufficiency, 21-hydroxylase antibodies can support autoimmune adrenalitis. Depending on history and antibody findings, imaging can assess hemorrhage, infection, infiltration, or malignancy. Very-long-chain fatty acids may be relevant in males when adrenoleukodystrophy is possible. Tuberculosis and other infections depend on epidemiology and immune status.

For central disease, evaluation may include other pituitary hormones and pituitary MRI: a history of exogenous glucocorticoid use often provides the explanation, but tapering and recovery assessment should follow an evidence-based plan. The 2024 joint European and Endocrine Society guideline emphasizes that risk depends on both dose and duration and that biochemical recovery is variable.

The workup is complete only when it answers three questions: Is cortisol reserve inadequate? Where in the axis is the defect? What caused it? Urgency can change the order in which you get them, but not the need for each answer.