Plasma Free Cortisol in States of Normal and Altered Binding Globulins: Implications for Adrenal Insufficiency Diagnosis.

ABSTRACT

CONTEXT Accurate diagnosis of adrenal insufficiency is critical because there are risks associated with overdiagnosis and underdiagnosis. Data using liquid chromatography tandem mass spectrometry (LC/MS/MS) free cortisol (FC) assays in states of high or low cortisol-binding globulin (CBG) levels, including cirrhosis, critical illness, and oral estrogen use, are needed. DESIGN: Cross-sectional. OBJECTIVE: Determine the relationship between CBG and albumin as well as total cortisol (TC) and FC in states of normal and abnormal CBG. Establish the FC level by LC/MS/MS that best predicts TC of <18 µg/dL (497 nmol/L) (standard adrenal insufficiency diagnostic cutoff) in healthy individuals. SUBJECTS: This study included a total of 338 subjects in four groups healthy control (HC) subjects (n = 243), patients with cirrhosis (n = 38), intensive care unit patients (ICU) (n = 26), and oral contraceptive (OCP) users (n = 31). MAIN OUTCOME MEASURE(S) FC and TC by LC/MS/MS, albumin by spectrophotometry, and CBG by ELISA. RESULTS: TC correlated with FC in the ICU (R = 0.91), HC (R = 0.90), cirrhosis (R = 0.86), and OCP (R = 0.70) groups (all P < 0.0001). In receiver operator curve analysis in the HC group, FC of 0.9 µg/dL (24.8 nmol/L) predicted TC of <18 µg/dL (497 nmol/L; 98% sensitivity, 91% specificity; AUC, 0.98; P < 0.0001). Decreasing the cutoff to 0.7 µg/dL led to a small decrease in sensitivity (92%) with similar specificity (91%). CONCLUSIONS: A cutoff FC of <0.9 µg/dL (25 nmol/L) in this LC/MS/MS assay predicts TC of <18 µg/dL (497 nmol/L) with excellent sensitivity and specificity. This FC cutoff may be helpful in ruling out adrenal insufficiency in patients with binding globulin derangements.