No, it doesn’t! Although there is a diurnal variation in serum cortisol level, time of the day does not have an appreciable impact on the synthetic ACTH, also known as cosyntropin (Cortrosyn), stimulation test results.
A 2018 retrospective cohort study found that outcomes from cosyntropin stimulation (CS) testing was not affected by time of the day (0800-1000 h vs 1001-1200 h vs after 1200 h).1
An experimental study involving healthy volunteers with normal adrenal function also found that the time of day of CS testing (250 mcg IV) did not influence the peak or the delta of cortisol levels when measured by immunoassay.2 Similarly, an experiment involving normal volunteers concluded that while compared to testing at 0800 h the afternoon (1600) cortisol response to CS was more pronounced at 5 and 15 min, there was no significant difference in cortisol levels at 30 min.3 Parenthetically, peak cortisol level is usually obtained at 1 h after IV cosynstropin administration.
So if you think your patient should undergo CS testing, there is no reason to wait until the next morning!
Bonus Pearl: Did you know that while the half-life of cortisol is between 70-120 min, the half-life of cosyntropin is only 15 min? 4
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- Munro V, Elnenaei M, Doucette S, et al. The effect of time of day testing and utility of 30 and 60 min cortisol values in the 250 mcg ACTH stimulation test. Clin Biochem 2018;54:37-41. https://www.ncbi.nlm.nih.gov/pubmed/29458002
- Jonklaas J, Holst JP, Verbalis JG, et al. Changes in steroid concentration with the timing of corticotropin stimulation testing in participants with adrenal insufficiency. Endocr Pract 2012;18:66-75. https://www.ncbi.nlm.nih.gov/pubmed/21856601
- Dickstein G, Shechner C, Nicholson WE, et al. Adrenocorticotropin stimulation test: effect of basal cortisol level, time of day, and suggested new sensitive low dose test. J Clin Endocrinol Metab 72:773-78. https://www.ncbi.nlm.nih.gov/pubmed/2005201
- Hamilton DD, Cotton BA. Cosyntropin as a diagnostic agent in the screening of patients for adrenocortical insufficiency. Clinical Pharmacology Advances and Applications 2010;2:77-82. https://www.ncbi.nlm.nih.gov/pubmed/22291489
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