Subjects: We try to analyze the prediction capacity of variable factors to diagnose adrenal insufficiency. Methods: We analyzed clinical and laboratory data of 23 children (Male = 13) who have been checked regular dose ACTH stimulation test for suspected symptoms after HSCT (Lymphoid leukemia=6, Myeloid leukemia=9, Non-malignant=8) at the Catholic HSCT center from Feb 2013 to Feb 2017 at Seoul St. Mary’s Hospital. A normal response of ACTH stimulation test was defined as a stimulated serum cortisol ＞18.1 mcg/dl and an increment from base line of at least 7.2 mcg/dl was considered a partial response (1). Results : The suspected symptoms of AI that patients had before ACTH test were as follows: Poor feeding=9, Lethargy or sleeping tendency=7, Nausea or vomiting=6, Fever=6, Elevated ACTH or Low cortisol=2, Facial flushing=2, Hyperkalemia=1, Diaphoresis=1, Fatigue=1, Hyponatremia=1, Hypoglycemia=1, Edema=1, Epigastric pain=1, Dizziness=1. Sixteen (70%) out of 23 patients underwent ACTH test was diagnosed as AI, 4 patients were partial AI and 3 patients were normal. In AI group, serum cortisol levels after 60 minutes (3.82 ± 0.68 vs. 23.93 ± 8.18, P0.049) was lower and serum K level (4.30 ± 0.07 vs. 3.64 ± 0.18, P0.01) before ACTH stimulation test and rate of steroid use at the time of test (75% vs. 14.2%, p0.02) were higher than normal or partial response group. There were no significant differences age at HSCT, Age at ACTH test, serum FBS, Na level before ACTH test between AI and normal or partial response group. In a univariate logistic regression analysis,serum K level before ACTH test and rate of steroid use at the time of test were associated with AI respectively (OR=461.3; 95% CI, 1.1-191705.1, P 0.046) (OR=18.0; 95% CI, 1.6-198.51, p0.02). Conclusion: These results emphasize the need to pay attention to the small signal including serum normal upper limit K level and steroid use of children after HSCT for early detecting AI. 1. Rix M, Birkebaek NH, Rosthoj S, Clausen N. Clinical impact of corticosteroid-induced adrenal suppression during treatment for acute lymphoblastic leukemia in children: a prospective observational study using the low-dose adrenocorticotropin test. The Journal of pediatrics. 2005;147(5):645-50.