Every parent wishes for their child to have a healthy life. Newborn screening programs help make this possible by checking certain health conditions early on. Among the conditions included in this programme is Congenital Adrenal Hyperplasia (CAH).
CAH is a group of disorders causing problems in hormone production from the adrenal glands. These conditions are inherited in an autosomal recessive way – meaning that only individuals who have two altered copies of a gene are affected with the condition.
Hormones are important messengers in our body. In CAH, faulty adrenal hormone production leads to different presentations and symptoms. There are several forms of CAH and the most common form is 21-hydroxylase deficiency, which affects about 1 in 10000 to 20000 people in the world.
Although CAH is a lifelong condition, with early screening and diagnosis, standardized treatment, and regular follow-ups, most children with CAH can grow, study and work normally, and lead fulfilling lives. This practical handbook aims to provide families with a clear understanding of CAH. As each child’s symptoms may differ, the following sections focus mainly on the most common type – 21-hydroxylase deficiency CAH.
The adrenal glands sit on top of the kidneys and act as a “factory” that produces essential hormones (cortisol, aldosterone, sex hormones). CAH occurs because one “key component” in a specific production line (21-hydroxylase enzyme) is faulty, leading to decreased production of cortisol and aldosterone. The brain’s pituitary gland senses that there is not enough cortisol and pumps out extra ACTH—a signaling hormone that pushes the adrenal glands to work harder. This does not fix the cortisol shortage because the blocked enzyme step prevents normal cortisol production; instead, it overloads the pathway, causing the adrenals to churn out even more male hormones (androgens).
↓Cortisol
Essential for maintaining normal blood pressure, blood sugar and energy level. It also helps the body cope with illnesses and physical stress.
↓Aldosterone
Helps regulate the body’s water and salt balance. When levels are too low, the body loses water and salt through urine, leading to dehydration and low blood salt level.
↑Androgen (male hormone)
Promote the development of male sexual characteristics
Because of these hormone imbalances, children with CAH experience the following:
There are different severities of enzyme deficiency leading to a wide spectrum of clinical presentation:
Newborn screening for CAH is implemented in many places around the world, including Hong Kong, Shanghai etc. It involves a quick check of a few drops of your baby’s blood to see if certain hormone levels, especially 17-OHP, are unusually high. A positive screening result means that the baby has a higher risk of CAH and needs further confirmatory tests. The medical team will arrange detailed investigations, including a genetic test, to confirm or rule out CAH.
In rare occasions or in milder cases, CAH may not be detected through newborn screening. With symptoms suggestive of CAH, the medical team will use blood and urine tests, as well as genetic analysis, to make a definitive diagnosis.
Once CAH is diagnosed, treatment should start immediately. Our treatment goal is: "replace what is lacking, suppress what is excessive". In other words, we use medications to replace the missing hormones while suppressing the high levels of androgen, thus allowing the child to grow normally.
Main Medications
Your child will need regular follow-up visits to monitor growth, pubertal development, and blood pressure changes. In addition, blood tests are required to check electrolyte and hormone levels (including 17OHP and androgen). Bone age assessment should also be performed regularly to ensure that treatment remains effective and appropriate.
For adolescents and adults who have completed growth, the doctor may consider switching hydrocortisone to a longer-acting steroid, such as prednisolone or dexamethasone, to reduce the number of daily doses.
As your child enters adulthood, they will transition to lifelong monitoring with an adult endocrinologist. This includes regular checks for metabolic health (like blood pressure, blood sugar, and bone health), hormone balance, and reproductive function. Staying active helps prevent long-term health issues and promotes overall physical and mental well-being.
CAH is an autosomal recessive disorder. A child develops the disease only when they inherit two abnormal CYP21A2 genes — one from each parent. Individuals carrying only one abnormal gene are called carriers and show no symptoms.
If both parents are carriers of a CAH gene mutation, for each pregnancy (regardless of the child's sex), there is a:
For patients with CAH, the risk of the child being affected depends on whether the partner carries the abnormal gene. Therefore, genetic counseling is recommended during family planning to understand the risk to future children and to consider prenatal genetic diagnosis.
If you have one child with CAH, prenatal diagnosis can be performed — chorionic villus sampling at 10–11 weeks or amniocentesis at 12–14 weeks — to check whether the fetus has CAH. Both procedures carry a small risk of miscarriage.
In addition, at highly specialized prenatal diagnostic centres, non-invasive prenatal testing (NIPT) may be considered. This test uses a sample of the mother’s blood to look at the baby’s DNA and check if the baby may have CAH.
From around the 6th week of pregnancy, the medical team may prescribe a steroid (dexamethasone) to reduce the risk and severity of male-like changes to a baby girl's genitals if the fetus has CAH. This treatment must start early because genital development happens very early in pregnancy. However, this practice remains controversial and may carry side effects for the mother, such as gestational diabetes, high blood pressure, and weight gain. The potential benefits and risks should be carefully discussed with the obstetrics team.
In recent years, researchers have made strides in the management of CAH:
These innovations bring hope for improved, more personalized care and better long-term outcomes for people with CAH.
Taking care of CAH is like a “marathon”, not a “sprint”. It takes teamwork between the medical team, your child, and the family to help your kid grow up strong and happy.
Love and care help your child bloom and thrive in a healthy, caring environment. Our trust and teamwork make all the difference in treatment. Let’s team up and keep going for your child’s bright future!
Endocrine and Diabetes Team, Hong Kong Children’s Hospital
Dr. Sarah Poon
Dr. Yao Chen
Paediatric Endocrinologist from Shanghai Children's Medical Center, Shanghai Jiao Tong University School of Medicine; contributed during her clinical attachment in Hong Kong)
Dr Joanna Tung
Dr Gloria Pang
Dr Suki Chan
Dr Karen Ng (Paediatric Adolescent Gynaecology)
Dr Peter Tam (Paediatric Surgery)
Dr Sammi Wong (Paediatric Surgery)
Dr Terry Law and Mr Kento Nakano for graphic design support
January 2026