Prevalence of adrenal insufficiency (AI) requiring treatment with hydrocortisone in children tested with the LDSST

Julie Park; Bhavana Selvarajah; Andrew Titman; Joanne Blair

Synacthen tests are used widely in paediatric practice for diagnosis of AI. The standard dose test may be more specific and low dose test (LDSST), more sensitive. The LDSST requires dilution of commercially available Synacthen, which may result in unreliable dosing and over diagnosis of AI.

Aim: To determine the prevalence of AI requiring treatment with hydrocortisone (a) daily (peak cortisol <350nmol/l) (b) on sick days only (peak cortisol 350-499nmol/l), in children tested with the LDSST, according to the indication for testing.

Methods: Retrospective analysis of LDSSTs (Synacthen 500ng/1.73m², sampling 0’,15,25’,35’) performed between 2008 and 2020. Only the first test was included if a child had >1 test.

Results: Data from 494 (296 M) children, age 9.5 (±5.2) were analysed. Mean peak cortisol differed significantly between groups, adjusting for age, gender and including baseline cortisol as a predictor (F-test P < 0.0001). Peak cortisol was lowest in other iatrogenic (previous anti-inflammatory glucocorticoids), structural brain abnormalities and infants, whilst highest in fatigue, GHD and those with autoimmune disease.

Table 1 Cortisol concentrations in patients undergoing the LDSST, and indication for testing.
Indication for test (N)	Age (years)	Baseline cortisol (nmol/l)	Peak cortisol (nmol/l)	Peak cortisol 350-449nmol/l) (%)	Peak cortisol <350nmol/l(%)
All (494)	9.3±7.5	223±123	513±166	85(17)	67(14)
ICS (106)	10.4±3.6	187±84	429±119	27(24)	22(21)
Other iatrogenic (40)	9.7±5.8	197±91	410±150	8(20)	12(30)
Structural brain abnormality (136)	9.2±4.9	245±125	556±161	15(11)	13(10)
Fatigue (37)	11.7±4.5	236±117	583±85	1(3)	0
Poor cortisol response to GH stim test (29)	9.9±4.5	236±86	649±88	3(10)	0
GHD (30)	9.4±4.5	241±85	639±137	3(15)	1(4)
Infants (35)	0.3±0.3	183±188	465±249	9(26)	13(37)
Autoimmune (19)	14.2±2.0	306±202	566±186	3(26)
Miscellaneous (66)	10.1±5.4	227±128	546±178	9(14)	7(9)
ICS: inhaled corticosteroids; GHD: growth hormone deficiency

Discussion: Thresholds for the prescription of hydrocortisone daily or on sick days only are derived from children tested following adrenal crisis during ICS therapy. Using these thresholds, 14% were prescribed daily hydrocortisone. The significance of cortisol peaks 350-449nmol/l is uncertain. Treatment on sick days only in children with a result in this range, together with education for the symptoms of AI, should reduce the risk of overtreatment.

ESPE Abstracts

P2-22