IMPE Abstracts

Background: Cortisol level in human follows circadian rhythm. In surveillance for potential cortisol deficiency in at risk population, for instance, in cancer survivors who received cranial irradiation, the screening will be checking 8am morning cortisol. Often, it is too early for patients to attend the clinic for blood sampling, especially for those living far away. This study aims to delineate the correlation of dried blood spot cortisol with plasma cortisol, such that we could further examine the feasibility of using dried blood spot cortisol as a possible alternative to allow for home-based sampling.

Methods: Retrospective review of all the paired dried blood spot and plasma cortisol samples taken from 2021 to 2022 in the Hong Kong Children’s Hospital. The dried blood spot cortisol samplings were processed by liquid chromatography tandem mass spectroscopy (LC-MS/MS), whereas the plasma cortisol samples were processed by Roche cobas e801 Elecsys Cortisol II assay. Correlation analysis and Linear regression were employed to define the relationship between dried blood spot cortisol and plasma cortisol.

Results: We have retrospectively reviewed 278 paired dried blood spot and plasma cortisol samples collected from 51 individuals who had undergone a total of 57 endocrine tests (33 low dose Synacthen stimulation tests, one cortisol profiling, 19 Glucagon stimulation tests, two morning cortisol samples and two random cortisol samples) were included in analysis. The median age of participants was 11.88 years (Range 1month - 19.64 years) with female to male ratio of 1:1. The primary disease conditions included oncological conditions (n=23), hematological conditions (n=9), general endocrine disorders (n=14), gastrointestinal disorders (n=2), skeletal dysplasia (n=1), rheumatological disorder (n=1), neurological conditions (n=2), mitochondrial disorder (n=1), dermatological disorder (n=1), genetic disorder (n=1). The dried blood spot cortisol is highly correlated to plasma cortisol levels (r=0.98). Linear regression showed plasma cortisol in nmol/l = 73.83 + 1.38 x dried blood spot cortisol in nmol/l (Goodness-of-fit assessed by R2 = 0.97).

Conclusion: Dried blood spot cortisol assay correlates well with plasma cortisol assay. Future studies to delineate the dried blood spot morning cortisol cut-off for adrenal insufficiency screening and practical feasibility of home-based dried blood spot sampling can render morning cortisol testing more convenient for patients.