Two‐day low‐dose dexamethasone suppression test more accurate than overnight 1‐mg in women taking oral contraceptives

Abstract

Abstract Introduction 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. 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. Objective To 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). 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). Salivary cortisol was also measured at late night and after the DSTs. Results Following 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 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. 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.

Keywords

• Cushing's syndrome
• dexamethasone suppression test
• false positive
• oral contraception