The low-dose ACTH stimulation test: is 30 minutes long enough?

OBJECTIVE: Controversy persists regarding the use of the low-dose adrenocorticotropic hormone (ACTH) stimulation test (LDST) for the diagnosis of adrenal insufficiency (AI) and optimal test result interpretation. However, many centers are now using the LDST to assess cortisol secretion adequacy, and some only use a 30-minute cortisol level to determine adrenal sufficiency or AI. This study examined both 30- and 60-minute cortisol levels to assess whether the interpretation of the test was affected when both cortisol levels were taken into consideration.

METHODS: Data were obtained by retrospective chart review from a single pediatric endocrinology unit over a 7-year period. We identified 82 patients who completed the LDST. Their mean age was 11.7 years, and 37% were female. Cortisol levels were evaluated at baseline and 30 and 60 minutes after cosyntropin administration. A cutoff value ≥18 μg/dL was used to define adrenal sufficiency.

RESULTS: We found that 54% of patients reached peak cortisol levels at 60 minutes, and 11 patients who did not pass the test at 30 minutes did so at 60 minutes. The only predictive characteristic was weight status; overweight and obese individuals tended to peak at 30 minutes, and normal and underweight individuals tended to peak at 60 minutes.

CONCLUSION: Although further studies are necessary to confirm our findings, it appears that measuring cortisol both 30 and 60 minutes following synthetic ACTH administration may be necessary to avoid overdiagnosing AI.