Annals of Clinical Biochemistry > Volume 46, Number 6 > Pp. 505-507

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Short Reports

Serum total cortisol and free cortisol index give different information regarding the hypothalamus–pituitary–adrenal axis reserve in patients with liver impairment

Royce P Vincent¹, Frédérique E Etogo-Asse², Tracy Dew¹, William Bernal², Jamshid Alaghband-Zadeh¹ and Carel W le Roux¹

¹ Department of Chemical Pathology; ² Institue of Liver Studies, King's College Hospital NHS Foundation Trust, Denmark Hill, London SE5 9RS, UK

Corresponding author: Dr Carel W le Roux. Email: c.leroux{at}imperial.ac.uk

Background: The short synacthen test (SST) is used to investigate patients with suspected hypothalamus–pituitary–adrenal (HPA) axis pathology. A rise of serum total cortisol (total cortisol) above 550 nmol/L is accepted as sufficient adrenal reserve. In total, 80% of cortisol is bound to cortisol-binding globulin (CBG) and 10% to albumin. In the acute phase responses CBG concentrations decrease and can influence the interpretation of SST. The free cortisol index (FCI) is a surrogate marker for free cortisol and is defined as total cortisol (nmol/L)/CBG (mg/L) with an FCI > 12 representing sufficient adrenal reserve. The aim of this study was to compare total cortisol and FCI in the interpretation of SST in patients with liver impairment.

Method: SST was done on 26 patients with liver impairment. Total cortisol was measured on Advia Centaur; serum CBG by radioimmunoassay and FCI calculated.

Results: Eleven (42%) patients had a total cortisol >550 nmol/L (range 555–2070) and FCI > 12 (12.0–68.9) suggesting sufficient cortisol reserve. Three patients (13%) had total cortisol <550 nmol/L (268–413) and FCI < 12 (3.5–11.6) consistent with cortisol deficiency. Twelve patients (46%) had a total cortisol <550 nmol/L (144–529), but an FCI > 12 (12.0–52.9). None of the patients had a total cortisol >550 nmol/L and FCI < 12.

Conclusion: When total cortisol alone is used to interpret SST in patients with liver impairment, 46% may have been classified as having adrenal insufficiency because of low CBG. FCI may be better for the evaluation of HPA axis insufficiency in patients with liver impairment.

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