Renal Tubular Acidosis

Each time our internal organs do something, such as digesting food or healing damaged tissue, chemical reactions take place in the body's cells. These reactions cause acid to go into the bloodstream.

Normally, the kidneys remove excess acid from blood, but certain diseases, genetic defects, or drugs can damage a kidney's ability to do this important job. This can allow too much acid to build up in the blood and cause problems. When this happens, it's called renal tubular acidosis (RTA).

Without treatment, RTA can affect a child's growth and cause kidney stones, fatigue, muscle weakness, and other symptoms. Over time, untreated acidosis can lead to long-term problems like bone disease, kidney disease, and kidney failure.

Fortunately, such complications are rare, since most cases of RTA can be effectively treated with medicines or by treating the condition that's causing the acid to build up.

How the Kidneys Work

The kidneys are a pair of bean-shaped organs located toward the back of the abdominal cavity, just above the waist. The kidneys remove waste products and extra water from the food a person eats, returning chemicals the body needs (such as sodium, phosphorus, and potassium) back into the bloodstream. The extra water combines with other waste to become urine (pee).

The main functional units of the kidneys, where the blood filtering happens, are tiny structures called nephrons. Each kidney has about a million nephrons, and each nephron has a renal tubule, a tube where the acid and waste products filtered from the blood are secreted into urine.

Having a disease or defect can interfere with how the renal tubules function, which can lead to RTA.

Causes

There are a few different kinds of RTA. The first two types are named for the part of the renal tubule in which the damage or defect is found.

• Type 1 RTA, or distal renal tubular acidosis, is the most common kind of RTA. Distal means that the defect is relatively far from the beginning of the tubule. Distal RTA can be inherited or caused by high blood calcium, sickle cell disease, autoimmune disorders like lupus and Sjogren syndrome, or the use of certain drugs.
• Type 2 RTA, or proximal renal tubular acidosis, happens when the damage or defect is relatively close to the start of the tubule. Proximal RTA mostly happens in infants and usually is related to a disorder called Fanconi's syndrome. Vitamin D deficiency, fructose intolerance, the use of certain drugs, and some diseases also can cause proximal RTA.
• Type 3 RTA is a combination of distal RTA and proximal RTA and is rarely used as a classification anymore.
• Type 4 RTA, or hyperkalemic renal tubular acidosis, is caused by a transport disorder in the distal tubule. Transport involves the movement of electrolytes such as sodium, chloride, and potassium between the blood and body parts. When this process is abnormal, it can cause too much potassium to build up in the blood (hyperkalemia). This can be a problem for the heart and other organs. Hyperkalemic RTA can be caused by urinary tract infections (UTIs), autoimmune disorders, sickle cell disease, diabetes, kidney transplant rejection, or the use of certain drugs.

Symptoms

A lot of the time, kids with RTA don't have any symptoms and may not know they have the disease until it shows up on a blood or urine test.

For some kids, the first symptom of RTA is kidney stones, which can cause symptoms like:

• pain in the back or side that spreads to the lower abdomen
• pain while urinating
• pee that is red, brown, or cloudy
• frequent urge to urinate
• nausea and vomiting

Over time, RTA can affect bone development and keep a child from growing as much as he or she should. This is often why doctors suspect RTA in the first place.

Other symptoms of RTA you might notice include:

• confusion, decreased alertness, or fatigue
• increased breathing and heart rates
• decreased urination
• muscle weakness
• muscle cramps and pain in the back and abdomen
• rickets (a disorder that can cause bone pain and skeletal and dental deformities)

Diagnosis

If your child shows any symptoms of RTA, see a doctor right away. The sooner something is done about the condition, the more effective treatment will be.

To diagnose RTA, the doctor will do a physical examination and take a sample of your child's blood for testing. He or she also may want a urine sample. If test results suggest that your child might have RTA, the doctor will work with you to decide the best way to treat it.

Treatment

How RTA is treated depends on what's causing it. If it's a reaction to a certain drug, treatment may involve stopping use of the drug or changing the dosage. If an underlying disease or other condition is causing RTA, it will be treated until that condition resolves.

To treat the effects of RTA, it's necessary to restore a normal acid level to the blood. To do this, doctors prescribe alkaline medicines, such as sodium bicarbonate, that help to lower the blood's concentration of acid.

Most of the time, treatment for RTA is effective. Kids whose RTA is caused by a genetic defect may need treatment for the rest of their lives. The good news is that sticking with their treatments lets kids remain healthy.