Why Do Babies With Salt-Wasting CAH Need Sodium Supplements?

Babies born with salt-wasting classic congenital adrenal hyperplasia (CAH) do not make enough of a hormone called aldosterone, which normally tells the kidneys to hold onto salt ^[1]. While they take a daily medication called fludrocortisone to replace this mineralocorticoid hormone, some babies still need extra liquid sodium chloride (salt) supplements. This is because a newborn’s developing kidneys are naturally less efficient at holding onto salt ^[1][2]. While fludrocortisone helps the kidneys work better, it may not be enough to overcome an infant’s high sodium needs, especially during their first 6 to 12 months ^[3][4].

Note: This page focuses on salt and fludrocortisone. Babies with classic CAH also require a daily glucocorticoid medication, typically hydrocortisone, to replace missing cortisol. All of these treatments work together and are essential for your baby’s health.

Adrenal Crisis and Sick Day Safety

It is important to know that managing your baby’s salt and fludrocortisone is only part of their care. If your baby is sick, vomiting, refusing to eat, or showing signs of dehydration (fewer wet diapers), unusual sleepiness, or weakness, they are at risk of a life-threatening adrenal crisis.

• Follow your sick-day plan: You must give stress doses of hydrocortisone as directed by your endocrinologist. Adjusting salt or fludrocortisone alone will not treat an adrenal crisis.
• Emergency action: If your baby is repeatedly vomiting and cannot keep oral medications down, or appears very weak or unresponsive, use your prescribed emergency hydrocortisone injection and seek immediate emergency medical care.

How the Body Handles Salt

In a body without CAH, the adrenal glands produce aldosterone, which works directly on the kidneys to keep sodium in the bloodstream. In salt-wasting CAH, inadequate aldosterone means the kidneys let too much sodium slip away into the urine ^[1].

Newborns and young infants are particularly vulnerable. In early life, infants have a natural, temporary resistance to the effects of aldosterone ^[1][2]. When you combine this natural immaturity with the low aldosterone caused by CAH, the risk of losing too much salt is increased when the condition is undertreated.

Why Fludrocortisone Isn’t Always Enough

Fludrocortisone replaces aldosterone, but international guidelines recommend adding an oral sodium chloride supplement for many infants during the first year of life ^[3][4].

There are two main reasons for this dual approach:

• Dietary sodium needs: Breast milk and standard infant formulas provide adequate sodium for healthy infants, but they may not provide enough to cover the extra sodium lost by a baby with salt-wasting CAH ^[3]. Do not alter formula concentrations or add table salt to feeds unless specifically instructed by your medical team.
• Finding a safe balance: Both excessive fludrocortisone and excessive sodium can cause fluid retention and high blood pressure, while too little can lead to salt wasting ^[3]. Prescribing them together allows doctors to individualize the doses safely for each baby.

Liquid Salt Safety and Administration

Liquid sodium chloride is a precise medication.

• Use the exact product: Concentrations can vary widely. Always use the exact pharmacy-prepared liquid, verify the dose in milliliters (mL) with your pharmacist, and use a proper oral syringe.
• Never substitute: Never use table salt, homemade saltwater, or a different brand/concentration without your endocrinologist’s direction.
• Missed or spit-up doses: Ask your care team in advance what to do if your baby spits up the salt supplement. Do not guess or try to make up the dose on your own.

How Long Will My Baby Need Supplements?

Many infants with salt-wasting CAH take a liquid salt supplement for their first 6 to 12 months, though the duration varies ^[3]. As your baby grows, their kidneys mature and become better at handling electrolytes ^[1]. While starting solid foods introduces more sodium into their diet, this does not automatically mean the supplement can stop. Your endocrinologist will use laboratory results, growth, and blood pressure to decide when and how to safely reduce the salt supplement.

Monitoring Your Baby’s Needs

To make sure your baby gets the right amount of salt, fludrocortisone, and hydrocortisone, your medical team will regularly check their weight, blood pressure, and blood work ^[3].

One of the key blood tests checks a hormone called renin.

• High renin levels can reflect inadequate sodium or fludrocortisone, but they can also be affected by dehydration, recent illness, or a baby’s age ^[5].
• Low or suppressed renin levels might indicate your baby is getting too much medication or salt, which increases the risk of high blood pressure ^[5].

Because renin is influenced by many factors, your doctor will look at it alongside your baby’s sodium, potassium, blood pressure, and growth. Never use a lab result to change doses on your own ^[5].