Interpretation of Urinary Free Cortisol Results
Your urinary free cortisol (UFC) level of 22.3 μg/24h (approximately 62 nmol/24h) is normal and does not suggest Cushing's syndrome or hypercortisolism. 1
Reference Range Context
The normal 24-hour urinary free cortisol excretion is typically <193 nmol/24h (<70 μg/m²/24h), and your value of approximately 62 nmol/24h falls well within this normal range 1
Multiple studies using liquid chromatography-tandem mass spectrometry (LC-MS/MS) have established upper reference limits ranging from 141-165 nmol/24h (approximately 51-60 μg/24h), with your value being substantially below these thresholds 2
Historical reference ranges from earlier immunoassay methods showed normal values averaging 77.22 ± 7.74 μg/24h in healthy subjects, with your result falling within one standard deviation of this mean 3
Clinical Significance for Cushing's Syndrome Screening
UFC values in confirmed Cushing's syndrome are typically >3-fold the upper limit of normal, with mean values around 488 μg/24h in affected patients—dramatically higher than your result 4, 3
Your UFC level of 22.3 μg/24h effectively rules out Cushing's syndrome, as there is typically no overlap between normal values and those seen in patients with adrenal hyperfunction 3
The Endocrine Society guidelines emphasize that UFC is most useful when significantly elevated; mild elevations (within 3-fold of normal) may represent pseudo-Cushing's states rather than true disease 4
Factors Affecting Interpretation
Urine volume and glomerular filtration rate strongly predict UFC levels, and your total volume of 1600 mL is within the normal range for adequate interpretation 4
Your urinary creatinine of 1.66 g/24h (assuming grams) is within the expected range for adequate 24-hour collection completeness in a 25-year-old female 4
Sex differences exist in UFC excretion, with women typically showing lower values (median 109-149 nmol/24h) compared to men, making your result even more reassuringly normal for your demographic 5
Clinical Recommendation
No further endocrine evaluation for hypercortisolism is warranted based on this normal UFC result. 4, 1 If clinical suspicion for Cushing's syndrome remains high despite this normal result, alternative screening tests such as late-night salivary cortisol (normal <3.6 nmol/L) or overnight 1-mg dexamethasone suppression test (normal cortisol <1.8 μg/dL) should be considered, as at least 2-3 abnormal screening tests are recommended before pursuing definitive diagnostic workup 4, 1