What is the normal morning cortisol level for a 39-year-old female?

Normal Morning Cortisol for a 39-Year-Old Female

The normal morning cortisol range for a 39-year-old female is 140–700 nmol/L (5.1–25.4 μg/dL) when measured at 8:00-9:00 AM, which represents the physiologic peak of cortisol secretion. 1

Reference Ranges by Time of Day

Morning cortisol levels follow a strict circadian rhythm that is critical for accurate interpretation:

• 8:00-9:00 AM (optimal testing window): 140–700 nmol/L (5.1–25.4 μg/dL) 1
• Midnight levels: 80–350 nmol/L (2.9–12.7 μg/dL) 1
• Physiologic pattern: Cortisol peaks in early morning (8:00-9:00 AM) and progressively declines throughout the day to reach its nadir at midnight 1

Critical Timing Requirements

The 8:00-9:00 AM window is mandatory for reliable assessment of adrenocortical function, as this timing captures the physiologic peak with optimal sensitivity and specificity for detecting both hypercortisolism and adrenal insufficiency 1. Drawing cortisol outside this window renders interpretation unreliable and potentially misleading 1.

Clinical Interpretation Thresholds

When evaluating morning cortisol results in the appropriate 8:00-9:00 AM timeframe:

• >14 μg/dL (>386 nmol/L): Effectively rules out adrenal insufficiency 2
• >13 μg/dL (>358 nmol/L): Reliably excludes adrenal insufficiency 3
• >375 nmol/L (>13.6 μg/dL): Predicts adequate adrenal function with 95% specificity 4
• <50 nmol/L (<1.8 μg/dL): Strongly suggests adrenal insufficiency and requires further evaluation 5
• <110 nmol/L (<4.0 μg/dL): Likely indicates subnormal cortisol response to ACTH stimulation 6

Common Pitfalls to Avoid

Never interpret a single cortisol value without documenting the exact collection time, as the same numerical value may be normal at 9:00 AM but pathologically elevated at midnight 1. This is the most common error in cortisol interpretation.

Additional critical considerations:

• Shift workers and patients with disrupted circadian rhythms should not undergo morning cortisol testing, as their cortisol peaks occur at different times and will yield unreliable results 1
• Document all medications affecting cortisol binding globulin (CBG): oral estrogens, pregnancy status, and chronic active hepatitis increase total cortisol levels and lead to false interpretation 1
• Avoid recent physical or mental stress: patients should avoid strenuous exercise for 24-48 hours before testing, as stress significantly elevates cortisol 1
• CYP3A4-inducing medications (anticonvulsants, rifampin, anti-tuberculosis drugs) increase cortisol clearance and may lower measured levels 7, 2

When Additional Testing Is Required

For morning cortisol values in the intermediate range (between clear normal and clear abnormal):

• Values between 110-300 nmol/L (4.0-10.9 μg/dL): Require dynamic testing with ACTH stimulation test to definitively rule in or rule out adrenal insufficiency 6
• Suspected cyclic Cushing's syndrome: Single measurements may miss hypercortisolemic phases; serial measurements over weeks are necessary 2
• Suspected autonomous cortisol secretion: The 1 mg overnight dexamethasone suppression test is the preferred screening test, with cortisol measured at 8:00 AM following 11:00 PM dexamethasone administration 1

Integration with ACTH Measurement

When measuring both ACTH and cortisol together, both must be drawn simultaneously at 8:00-9:00 AM from the same blood draw to distinguish primary from secondary adrenal insufficiency 1:

• Primary adrenal insufficiency: ACTH elevated (>1.1 pmol/L or >5 ng/L) with low cortisol 1
• Secondary (central) adrenal insufficiency: Both ACTH and cortisol are low 1
• ACTH-dependent hypercortisolism: Morning ACTH >1.1 pmol/L (>5 ng/L) with elevated cortisol has 68% sensitivity and 100% specificity 7, 1

ACTH is extremely labile and requires immediate processing on ice, so coordinate with the laboratory before drawing to ensure proper handling 1.