Laboratory Abnormalities Associated with Elevated Cortisol Levels
Elevated cortisol levels (hypercortisolism/Cushing syndrome) are associated with hyperglycemia, hypokalemia, hypertension, and metabolic alkalosis, along with elevated triglycerides and increased cardiovascular risk markers. 1
Primary Metabolic Abnormalities
When cortisol is chronically elevated, the following laboratory changes occur:
Glucose Metabolism
- Hyperglycemia and impaired glucose tolerance are hallmark features
- Elevated fasting insulin and C-peptide levels
- Increased glycated hemoglobin (HbA1c)
- Elevated HOMA index (insulin resistance marker) 2
- The frequency of impaired glucose tolerance increases progressively with higher cortisol levels, even in nondiabetic patients
Electrolyte Disturbances
- Hypokalemia - caused by the mineralocorticoid effects of excess cortisol 1
- Metabolic alkalosis - secondary to potassium loss
- Sodium retention (though serum sodium may appear normal)
- These changes contrast sharply with adrenal insufficiency, where you see hyperkalemia and hyponatremia
Lipid Abnormalities
- Elevated triglycerides 2
- Increased LDL cholesterol
- Decreased HDL cholesterol 2
- These changes contribute to the metabolic syndrome phenotype seen in hypercortisolism
Hormonal Changes
ACTH Levels - Critical for Diagnosis
The ACTH level distinguishes the etiology:
- Suppressed or undetectable ACTH indicates adrenal-source Cushing syndrome (ACTH-independent) 1, 3
- Normal or elevated ACTH indicates pituitary or ectopic ACTH production (ACTH-dependent) 4
Other Hormonal Markers
- Elevated 24-hour urinary free cortisol (UFC) - values >4 times normal are diagnostic 3, 5
- Loss of circadian rhythm - elevated late-night salivary cortisol (normally should be very low) 3, 5
- Failure to suppress on dexamethasone suppression test - cortisol remains >1.8 µg/dL after 1mg overnight dexamethasone 3
Additional Laboratory Findings
Cardiovascular and Renal Markers
- Elevated uric acid 2
- Increased oxidized LDL (oxLDL) - marker of oxidative stress 6
- Decreased estimated GFR in hypertensive patients 7
- Elevated creatinine and cystatin C 7
Hematologic Changes
While these are more characteristic of low cortisol (adrenal insufficiency), it's important to note the contrast:
- In hypercortisolism: leukocytosis with lymphopenia may occur
- In adrenal insufficiency (opposite): anemia, eosinophilia, lymphocytosis 8
Clinical Pitfalls and Important Caveats
Pseudo-Cushing syndrome can mimic true hypercortisolism biochemically:
- Psychiatric disorders, alcohol use, obesity, and polycystic ovary syndrome can activate the HPA axis
- These conditions may show mildly elevated cortisol, UFC, and late-night salivary cortisol
- However, UFC is almost always <3-fold normal in pseudo-Cushing 9
- The Dex-CRH test or desmopressin test can help distinguish true Cushing syndrome from pseudo-Cushing
Assay-specific considerations:
- Cortisol-binding globulin (CBG) affects total cortisol measurements
- Oral estrogens, pregnancy, and chronic hepatitis increase CBG, falsely elevating total cortisol 9
- Second-generation immunoassays have different reference ranges than older assays 10
- Always measure dexamethasone levels concomitantly during suppression testing to avoid false results 9
Renal impairment affects testing:
- UFC becomes unreliable when creatinine clearance <60 mL/min 5
- Use late-night salivary cortisol instead in patients with renal disease 9
Diagnostic Algorithm
Screen with any of these tests (choose based on availability):
If screening positive, measure ACTH to determine source:
Confirm with additional testing if initial results equivocal:
- Dex-CRH test for pseudo-Cushing differentiation
- Midnight serum cortisol if hospitalized
- Repeat abnormal tests to account for cyclic disease 5