Abstract
IntroductionLate‐night salivary cortisol (LSaC) and 24‐h urinary free cortisol measurement, and overnight 1‐mg dexamethasone suppression test (1 mg‐DST) are the first‐line screening tests recommended for Cushing's syndrome. Through elevations in the level of cortisol‐binding globulin, oral contraceptive agents lead to increases in the total plasma cortisol concentration, yielding false‐positive 1 mg‐DST results.ObjectiveTo compare the accuracy of the overnight 1‐mg DST and two‐day low‐dose DST (2d‐DST) in female volunteers taking combined oestrogen‐progestin oral contraceptives (COCs).MethodsThis prospective study enrolled 30 healthy participants. Their plasma cortisol response levels were compared after the 1‐mg DST and 2d‐DST and classified into three categories: normal (≤50 nmol/L), doubtful (51–138 nmol/L) and abnormal (>138 nmol/L). Salivary cortisol was also measured at late night and after the DSTs.ResultsFollowing the 1‐mg DST and 2d‐DST, the plasma cortisol concentrations decreased to a median of 69 nmol/L and 37 nmol/L, respectively (p < 0.001). A statistically significant higher proportion of unclear or abnormal results were observed after the 1‐mg DST (63%) than after the 2d‐DST (27%) (p = 0.004). None of the values were >138 nmol/L after the 2d‐DST, while 11% of them were abnormal after the 1‐mg DST (p = 0.25). No LSaC value was abnormal.ConclusionOur results suggest that, when late‐night salivary cortisol is not available, the 2d‐DST could be a better screening option than the 1‐mg DST for women taking oral contraceptive agents who are reluctant to stop them. This finding requires confirmation in those with a suspicion of hypercortisolism.
Highlights
Late-night salivary cortisol (LSaC) and 24-h urinary free cortisol measurement, and overnight 1-mg dexamethasone suppression test (1 mg-DST) are the first-line screening tests recommended for Cushing's syndrome
Women taking oral contraceptive agents have higher total plasma cortisol concentrations owing to elevations in the levels of cortisol-binding globulin (CBG) and the stronger affinity to cortisol.8,11-14 in patients with an elevated CBG level, the measurement of the total plasma cortisol level may yield imprecise findings in the assessment of plasma free cortisol, resulting in a high rate of false positive (FP) results in the 1 mg-DST.15-17 among women using oral contraceptives, the 1 mg-DST FP rate is evaluated to be 50%
The responses to the plasma cortisol suppression tests were classified into normal (≤50 nmol/L), doubtful (51–138 nmol/L) and abnormal (>138 nmol/L), with the two last corresponding to FP results
Summary
Late-night salivary cortisol (LSaC) and 24-h urinary free cortisol measurement, and overnight 1-mg dexamethasone suppression test (1 mg-DST) are the first-line screening tests recommended for Cushing's syndrome. Methods: This prospective study enrolled 30 healthy participants Their plasma cortisol response levels were compared after the 1-mg DST and 2d-DST and classified into three categories: normal (≤50 nmol/L), doubtful (51–138 nmol/L) and abnormal (>138 nmol/L). Conclusion: Our results suggest that, when late-night salivary cortisol is not available, the 2d-DST could be a better screening option than the 1-mg DST for women taking oral contraceptive agents who are reluctant to stop them. This finding requires confirmation in those with a suspicion of hypercortisolism
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