Assessment of Morning Cortisol Level of 5.8 mcg/dL at 8:30 AM
A morning cortisol level of 5.8 mcg/dL at 8:30 AM is in the low-normal range and does NOT rule out adrenal insufficiency—this patient requires further evaluation with an ACTH stimulation test to definitively exclude adrenal insufficiency. 1, 2
Interpretation of This Specific Value
The normal morning cortisol range is 5-23 mcg/dL (138-635 nmol/L), with most healthy individuals clustering between 10-20 mcg/dL (276-552 nmol/L). 1, 2 Your patient's value of 5.8 mcg/dL falls at the very bottom of this reference range.
Morning cortisol levels >14 mcg/dL (>386 nmol/L) effectively rule out adrenal insufficiency, but values below this threshold require further testing. 1, 2 Since 5.8 mcg/dL is well below 14 mcg/dL, adrenal insufficiency cannot be excluded.
A morning cortisol ≥8.5 mcg/dL predicts normal adrenal response with high sensitivity and specificity, while levels >10.9 mcg/dL almost exclude ACTH-cortisol insufficiency. 2 Your patient's value of 5.8 mcg/dL falls below both of these reassuring thresholds.
Required Next Steps
Proceed with ACTH stimulation testing (synacthen/tetracosactide test) using 0.25 mg IM or IV, with peak serum cortisol <500 nmol/L (<18 mcg/dL) being diagnostic of primary adrenal insufficiency. 1, 2
Clinical Context to Evaluate
Before and during testing, assess for these specific features that increase suspicion for adrenal insufficiency: 1
- Unexplained collapse or hypotension
- Persistent vomiting or diarrhea
- Hyperpigmentation (suggests primary adrenal insufficiency)
- Hyponatremia, hyperkalemia, or acidosis
- Unexplained hypoglycemia
Critical Pitfalls to Avoid
Never delay treatment of suspected acute adrenal insufficiency for diagnostic testing—if the patient is acutely ill with hypotension or shock, treat empirically with hydrocortisone immediately. 1
Exogenous steroid use (oral prednisolone, dexamethasone, inhaled fluticasone) can suppress endogenous cortisol production and confound interpretation—verify medication history before proceeding. 1, 2
In the context of acute severe illness or sepsis, a cortisol level that appears "normal" may actually represent relative adrenal insufficiency (RAI), as stress should elevate cortisol substantially. 3, 2 In critically ill patients, random total cortisol <276 nmol/L (<10 mcg/dL) suggests RAI. 3
Special Considerations for Specific Populations
In critically ill patients with cirrhosis or sepsis, different diagnostic criteria apply: 3
- Random total cortisol <276 nmol/L (<10 mcg/dL) in the setting of critical illness suggests relative adrenal insufficiency
- Baseline serum-free cortisol <50 nmol/L or post-ACTH free cortisol <86 nmol/L indicates RAI
- Salivary cortisol <1.8 ng/mL (<0.18 mcg/dL) at baseline or increment <3 ng/mL (0.3 mcg/dL) after stimulation suggests RAI
If the patient is on oral contraceptives or estrogen therapy, total cortisol may be falsely elevated due to increased cortisol-binding globulin (CBG), but this would not explain a LOW value like 5.8 mcg/dL. 1, 4