Diagnosing Renal Tubular Disorders in Children

NYU Langone’s pediatric nephrologists are experts in identifying and treating kidney, or renal, problems in children. The kidneys are two bean-shaped organs located below the rib cage, one on each side of the spine. Their job is to keep water, mineral, and nutrient levels stable. Renal tubular disorders in children can upset this delicate balance. 

Filtering structures in the kidneys, called glomeruli, empty a substance called ultrafiltrate into a series of ducts known as renal tubules. Ultrafiltrate contains water, acids, and minerals such as calcium, magnesium, bicarbonate, and phosphate. These minerals aid in maintaining the health of nerves and muscles, including those in the brain, heart, lungs, and other vital organs. The renal tubules reabsorb needed amounts of water, minerals, and nutrients into the blood and excrete excess amounts into the urine.

Renal tubular disorders are a diverse group of conditions that develop when the renal tubules don’t work properly, disrupting the balance of water, minerals, and acids in the blood. 

Renal tubules have many components, each with highly specialized functions. Conditions that affect one part of the renal tubule may have a different impact on the body than those that affect another part of the structure.

Causes of Renal Tubular Disorders

Some renal tubular disorders occur when a child inherits a gene mutation that affects how the renal tubules work. These mutations can occur as part of a genetic syndrome. For example, Fanconi’s syndrome causes a decrease in blood levels of several minerals, amino acids, and glucose, and Liddle’s syndrome causes a buildup of sodium and a decrease in potassium in the blood. 

Renal tubular damage may also occur after taking certain medications, including chemotherapy drugs to treat cancer and lithium to treat mood disorders. Other renal tubular disorders are triggered by autoimmune conditions, such as lupus, rheumatoid arthritis, or Sjogren’s syndrome, but it isn’t known why. 

Symptoms and Health Effects

Many renal tubular disorders do not cause noticeable symptoms until they have been present for a long time. Because the renal tubule is made of highly specialized parts, symptoms depend on the part of the tubule that is damaged. 

Some renal tubular disorders make the blood too acidic. Others that increase blood levels of the mineral bicarbonate, a substance that neutralizes acid, make the blood too alkaline. Still others cause a buildup or deficiency in minerals such as potassium, chloride, sodium, or calcium.

High or low levels of acids or minerals can lead to a variety of serious health conditions. For instance, renal tubular disorders that interfere with the reabsorption of potassium or magnesium can affect muscles, including the heart. Children with this type of renal tubular disorder may have muscle cramps, nausea, vomiting, and an irregular heartbeat known as an arrhythmia. 

Some renal tubular disorders affect the kidneys’ ability to respond to certain hormones. One such disorder, called diabetes insipidus, prevents the kidneys from responding to antidiuretic hormone, which stops the kidneys from eliminating too much water.

If the kidneys can’t eliminate calcium, a child may develop kidney stones, which cause abdominal pain and increase the need to urinate. Children with diabetes insipidus may urinate excessively and feel very thirsty. 

Renal tubular disorders that interfere with the absorption of vitamin D can weaken bones, increasing the risk of fractures and slowing growth. 

Left untreated, renal tubular disorders can cause chronic kidney disease. 

A pediatric nephrologist uses a physical exam and laboratory tests to diagnose renal tubular disorders. Imaging tests may also be recommended to help detect kidney stones.

Physical Exam

A pediatrician may suspect a renal tubular disorder if your child stops growing normally or has a change in the frequency of urination. During a physical exam, your child’s doctor asks about your child’s birth and medical history, paying particular attention to whether you have a family history of kidney or autoimmune disorders. He or she also asks about your child’s symptoms, such as urination problems or muscle cramps. 

The doctor tests your child’s reflexes to look for signs of muscle or nerve problems. Measuring blood pressure and listening to heart rhythm can help determine if the kidneys and heart are working as they should. 

Reviewing the growth chart may show the doctor whether your child is getting enough nutrients to grow as expected. 

Laboratory Tests

Pediatric nephrologists perform blood and urine tests to determine whether your child has the appropriate levels of minerals, such as bicarbonate, sodium, potassium, chloride, calcium, magnesium, and phosphorus. The doctor may also order blood tests to measure levels of blood urea nitrogen and creatinine; higher-than-normal levels can indicate poor kidney function.

Depending on your child’s medical history, symptoms, and test results, the doctor may recommend another blood test to look for the most common gene mutations associated with renal tubular disorders.  

Kidney Ultrasound

An ultrasound uses sound waves to form images of internal organs. The doctor may recommend ultrasound if your child has abdominal pain and difficulty urinating, which could indicate the presence of kidney stones. 

During this test, the doctor places a small device called a transducer on your child’s abdomen. The transducer bounces sound waves off of structures in the abdomen, producing an image of the kidneys.