353if done within 48h of life. In addition, preterm babies and those with neonatal
sepsis have elevated 17(OH)P, whereas newborns who have received prenatal
corticosteroid treatment to induce lung maturation may have low 17(OH)P lev-
els. Therefore, gestational age-specifi c 17(OH)P cutoffs should be used in
preterm babies and those with sepsis or have received corticosteroids should be
evaluated later. Estimation of 17(OH)P does not distinguish 21α-hydroxylase
defi ciency from 11β-hydroxylase defi ciency. Finally, the fi rst-tier screening
uses immunoassays for 17(OH)P which has marked cross-reactivity with other
steroid metabolites.- What is the role of ACTH stimulation test in neonatal screening for CAH?
It has been shown in various large scale neonatal screening programs for CAH that
the positive predictive value (PPV) of fi rst-tier screening test using 17(OH)P by
immunoassay is 0.8–1.07 % and PPV of second-tier test using 17(OH)P by
LC-MS/MS is 7.3 %. Therefore, confi rmatory test for the diagnosis of CAH is
required. This is accomplished by performing ACTH stimulation test (250 μg)
which is considered as a gold standard for the diagnosis of CAH. However, ACTH
stimulation test is not required in neonates with symptoms suggestive of CAH.- How to improve the outcome of neonatal screening program for CAH?
The outcome of neonatal screening program for CAH can be improved by esti-
mation of other steroid metabolites by LC-MS/MS. A ratio of the sum of serum
17(OH)P and 21-deoxycortisol divided by cortisol has been shown to improve
the PPV of second-tier test to 100 % when a cutoff of 0.53 was taken. 21-deoxy-
cortisol is a metabolite derived from 17(OH)P by the action of enzyme
11 β-hydroxylase, and 21-deoxycortisol levels are elevated in patients with
21 α-hydroxylase defi ciency.- What is the role of genotyping in the neonatal screening for CAH?
Genetic analysis has been suggested as a second-tier test in place of hormonal
profi ling by LC-MS/MS. This is because >90 % of children with CAH due to
21 α-hydroxylase defi ciency carry one of the ten common mutations of
21 α-hydroxylase gene, and genotyping can be performed on the same dried
blood spot used for the fi rst-tier screening. However, the test is very expensive,
requires expertise, and currently limited to detect CAH due to 21α-hydroxylase
defi ciency. Genetic analysis has not been validated as a second-tier test in com-
parison to hormone profi ling by LC-MS/MS in large studies. Although a nega-
tive genotyping makes a diagnosis of CAH highly unlikely, a positive genotyping
needs further confi rmation by stimulated 17(OH)P estimation as the positive
predictive value of genotyping is only 18 %.10 Congenital Adrenal Hyperplasia