Poster Presentation ESA-SRB-ANZBMS 2024 in conjunction with ENSA

A wolf in sheep’s clothing: Discrepancies in urinary free cortisol measurement methods in a case of adrenal Cushing’s syndrome (#634)

Sophie Templer 1 , Julie Hetherington 1 2 , Nimalie Perera 1 3 4 , Albert Hsieh 1 4
  1. Department of Endocrinology, Royal Prince Alfred Hospital, Sydney, NSW, Australia
  2. Susan Wakil School of Nursing and Midwifery, University of Sydney, Sydney, NSW, Australia
  3. Department of Chemical Pathology, NSW Health Pathology, Royal Prince Alfred Hospital, Sydney, NSW, Australia
  4. Faculty of Medicine and Health, University of Sydney, Sydney, NSW, Australia

Case: A 62-year-old woman was referred to the RPAH Endocrinology Clinic with a 27mm lipid-rich left adrenal incidentaloma. Background included gallstones with no regular medications. Her examination included mild hypertension (140/90mmHg) and no other features to suggest cortisol excess.

Workup included a normal aldosterone level with suppressed renin activity, and an abnormal saline suppression test (with 240min aldosterone 256pmol/L). Plasma metanephrine levels were within normal limits, as was 24-hour urinary free cortisol (UFC) measured by LC-MS/MS at 90nmol/day (RR<166). As primary aldosteronism was suspected, adrenal vein sampling (AVS) was performed that incidentally suggested left-sided cortisol excess with right-sided adrenal cortisol suppression.

Following this unexpected AVS result, repeat morning cortisol was 331nmol/L (RR 170-500) while ACTH was undetectable at <1.1pmol/L (RR≤10). Cortisol was unsuppressed at 378nmol/L (RR<50) after a 1mg dexamethasone suppression test, with a detectable dexamethasone level. Two late-night salivary cortisol levels were elevated at 11.6nmol/L and 10.9nmol/L (RR<3.2). Despite this, three further 24-hour UFC levels, measured by LC-MS/MS, were normal at 126nmol/day, 140nmol/day, and 91nmol/day (RR<166). When the last sample was sent to be measured by immunoassay, it was elevated to 279nmol/day (RR<270).

The patient underwent laparoscopic left adrenalectomy with histopathology confirming an adrenal cortical adenoma. She has required ongoing hydrocortisone replacement (now at two months post-surgery) for persistently low serum cortisol levels.

Discussion: This case highlights the diagnostic challenges in Cushing’s syndrome and the different levels of analytical consistency and diagnostic specificity of the commercially available immunoassays compared to the LC-MS/MS assay for UFC. Immunoassays typically have a positive bias compared to LC-MS/MS with high diagnostic accuracy due to cross-reactivity from cortisol precursors and metabolites that may not be detected by the highly specific LC-MSMS method,1,2,3 especially in biochemically mild cases of cortisol excess such as this case.4

  1. Casals, G., & Hanzu, F. A. (2020). Cortisol Measurements in Cushing's Syndrome: Immunoassay or Mass Spectrometry?. Annals of Laboratory Medicine, 40(4), 285–296.
  2. Oßwald, A., Wang, R., Beuschlein, F., Hartmann, M. F., Wudy, S. A., Bidlingmaier, M., Zopp, S., Reincke, M., & Ritzel, K. (2019). Performance of LC-MS/MS and immunoassay based 24-h urine free cortisol in the diagnosis of Cushing's syndrome. The Journal of Steroid Biochemistry and Molecular Biology, 190, 193–197.
  3. Mu, D., Fang, J., Yu, S., Ma, Y., Cheng, J., Hu, Y., Song, A., Zhao, F., Zhang, Q., Qi, Z., Zhang, K., Xia, L., Qiu, L., Zhu, H., & Cheng, X. (2024). Comparison of Direct and Extraction Immunoassay Methods With Liquid Chromatography-Tandem Mass Spectrometry Measurement of Urinary Free Cortisol for the Diagnosis of Cushing's Syndrome. Annals of Laboratory Medicine, 44(1), 29–37.
  4. Sheriff, N., & McCormack, A. I. (2017). How useful is urinary-free cortisol in the clinic?. Biomarkers in Medicine, 11(11), 1009–1016.