PERFORMANCE OF FREE VERSUS TOTAL CORTISOL FOLLOWING COSYNTROPIN STIMULATION TESTING IN AN OUTPATIENT SETTING.
OBJECTIVE
Free cortisol (FC) is potentially superior to total cortisol (TC) measurements in selected clinical settings; however, the advantages of uniform use of FC in outpatient settings are unclear. The objectives of this study were to describe the dynamic response of FC during cosyntropin stimulation testing (CST) compared to TC and to determine the rates of discordance.


METHODS
This is a cross-sectional study of 295 stable patients who underwent CST in an outpatient Endocrine Testing Center. The main outcome measures were TC and FC measurements during CST.


RESULTS
The mean age of the 295 subjects was 49.1 (16.9) years. Of 218 females, 43 were taking estrogen therapy (ET) at the time of testing. Adrenal insufficiency (AI) was diagnosed in 41/295 (14%) patients. The FC concentrations were associated with TC concentrations at baseline (R(2) = 0.77, P<.001), 30 minutes (R(2) = 0.87, P<.001), and 60 minutes (R(2) = 0.90, P<.001). The FC cutoffs for AI were 873 and 1,170 ng/dL at 30 and 60 minutes, respectively. The FC had a more pronounced fold change from baseline to peak than TC (median 3.2 vs. 1.7, P<.001). Both TC and FC at baseline were higher in females on ET compared to those who were not and to males; however, peak TC and FC values were similar. In 3/43 females on ET, FC, and TC results were discordant (P = .003).


CONCLUSIONS
We report 99% concordance of TC and FC measurements in a large outpatient cohort. The discordant rates were high in females treated with ET (7%). The FC measurements during CST in females on ET may provide a more rapid and accurate diagnosis of AI.
Irina
I
Bancos
Dana
D
Erickson
Sandra
S
Bryant
Jolaine
J
Hines
Todd B
TB
Nippoldt
Neena
N
Natt
Ravinder
R
Singh
D000309:Adrenal Insufficiency / Q000097:blood / Q000175:diagnosis*; D000324:Adrenocorticotropic Hormone / Q000097:blood; D000328:Adult; D000368:Aged; D003366:Cosyntropin / Q000008:administration & dosage*; D003430:Cross-Sectional Studies; D005189:False Positive Reactions; D005260:Female; D006801:Humans; D006854:Hydrocortisone / Q000032:analysis* / Q000097:blood; D008297:Male; D008875:Middle Aged; D010045:Outpatients; D010912:Pituitary-Adrenal Function Tests / Q000379:methods*; D012372:ROC Curve; D055815:Young Adult
D003366:Cosyntropin; D000324:Adrenocorticotropic Hormone; D006854:Hydrocortisone