using immunoassays is prone to cross-reactivity with various substances including 21-deoxycortisol that raises due to 21-hydroxylase deficiency, leading to falsely high cortisol levels when the true cortisol is actually low. The selectivity offered by liquid chromatography-tandem mass spectrometry (LC-MS/MS) has largely overcome these limitations. As a result, the use of LC-MS/MS instead of immunoassays in cortisol measurement aims to provide greater specificity. 11-Deoxycortisol is a direct product of 17α-hydroxyprogesterone, with 21-hydroxylase catalyzing the reaction, and an intermediate product towards cortisol pathway. Reduced 21-hydroxylase activity leads to decreased levels of 11-deoxycortisol, but not all laboratories specify minimum reference value it, since it is mostly used as a biomarker for 11β-hydroxylase deficiency, where 11-deoxycortisol levels increase dramatically, so the laboratories may only specify the maximum reference value. Treatment Prenatal treatment As of 2018, Clinical Practice Guideline advise that clinicians continue to regard prenatal therapy as experimental. Because the period during which fetal genitalia may become virilized begins about 6 weeks after conception, prenatal treatment to avoid virilization must be started by 6 to 7 weeks. Application of dexamethasone in prenatal treatment Adrenal glands of female fetuses with CAH begin producing excess androgens by the 9th week of gestation. The most important aspects of virilization (urogenital closure and phallic urethra) occur between 8 and 12 weeks. Theoretically, if enough glucocorticoid could be supplied to the fetus to reduce adrenal testosterone production by the 9th week, virilization could be prevented and the difficult decision about timing of surgery avoided. The challenge of preventing severe virilization of girls is twofold: detection of CAH at the beginning of the pregnancy, and delivery of an effective amount of glucocorticoid to the fetus without causing harm to the mother. The first problem has not yet been entirely solved, but it has been shown that if dexamethasone is taken by a pregnant woman, enough can cross the placenta to suppress fetal adrenal function. At present no program screens for risk in families who have not yet had a child with CAH. For families desiring to avoid virilization of a second child, the current strategy is to start dexamethasone as soon as a pregnancy has been confirmed even though at that point the chance that the pregnancy is a girl with CAH is only 12.5%. Dexamethasone is taken by the mother each day until it can be safely determined whether she is carrying an affected girl. Whether the fetus is