Hyperoxaluria (hi-pur-ok-suh-LU-ree-uh) happens when you have too much oxalate in your urine. Oxalate is a natural chemical the body makes. It's also found in some foods. But too much oxalate in the urine can cause serious problems.

Hyperoxaluria can be caused by a change in a gene, an intestine disease or eating too many foods that are high in oxalate. The long-term health of your kidneys depends on finding hyperoxaluria early and getting it treated quickly.

Oxalosis (ok-suh-LOW-sis) happens after the kidneys stop working well in people who have primary and intestine-related causes of hyperoxaluria. Too much oxalate collects in the blood. This can lead to oxalate buildups in blood vessels, bones and organs.

Often, the first sign of hyperoxaluria is a kidney stone. Kidney stone symptoms can include:

• Sharp pain in the back, side, lower stomach area or groin.
• Urine that looks pink, red or brown due to blood.
• Frequent urge to pee, also called urination.
• Pain when peeing.
• Not being able to urinate or peeing only a small amount.
• Chills, fever, upset stomach or vomiting.

When to see a doctor

It's not common for children to get kidney stones. Kidney stones that form in children and teenagers are likely to be caused by a health problem, such as hyperoxaluria.

All young people with kidney stones should have a checkup. The checkup should include a test that measures oxalate in the urine. Adults who keep getting kidney stones also should be tested for oxalate in the urine.

Hyperoxaluria happens when too much of a chemical called oxalate builds up in the urine. There are different types of hyperoxaluria:

• Primary hyperoxaluria. This type is a rare inherited disease, which means that it's passed down in families. It's caused by changes in a gene. With primary hyperoxaluria, the liver doesn't make enough of a certain protein that prevents too much oxalate from being made. Or the protein doesn't work as it should. The body gets rid of excess oxalate through the kidneys, in urine. The extra oxalate can combine with calcium to form kidney stones and crystals. These can damage the kidneys and cause them to stop working.

  With primary hyperoxaluria, kidney stones form early. They most often cause symptoms from childhood through age 20. The kidneys of many people with primary hyperoxaluria stop working well by early to middle adulthood. But kidney failure can happen even in babies with this disease. Others with primary hyperoxaluria may never have kidney failure.

• Enteric hyperoxaluria. Some intestine problems cause the body to absorb more oxalate from foods. This can then increase the amount of oxalate in the urine. Crohn's disease is one intestine problem that can lead to enteric hyperoxaluria. Another is short bowel syndrome, which can happen when parts of the small intestine are removed during surgery.

  Other health problems make it hard for the small intestine to absorb fats from food. If this happens, it might leave oxalate more available for the gut to absorb. Usually, oxalate combines with calcium in the gut and exits the body through stools. But when there is increased fat in the gut, calcium binds to the fat instead. This allows oxalate to be free in the gut and absorbed in the bloodstream. It's then filtered by the kidneys. Roux-en-Y gastric bypass surgery also can lead to trouble absorbing fat in the gut, which raises the risk of hyperoxaluria.

• Hyperoxaluria tied to eating foods with lots of oxalate. Eating large amounts of foods high in oxalate can raise your risk of hyperoxaluria or kidney stones. These foods include nuts, chocolate, brewed tea, spinach, potatoes, beets and rhubarb. It's important to stay away from high-oxalate foods if you have diet-related or enteric hyperoxaluria. Your doctor also may tell you to limit these foods if you have primary hyperoxaluria.

Without treatment, primary hyperoxaluria can damage the kidneys. Over time the kidneys may stop working. This is called kidney failure. For some people, this is the first sign of the disease.

Symptoms of kidney failure include:

• Peeing less than usual or not peeing at all.
• Feeling ill and tired.
• Not feeling hungry.
• Upset stomach and vomiting.
• Pale, ashen skin or other changes to skin color tied to having a low number of red blood cells, also called anemia.
• Swelling of hands and feet.

Oxalosis happens if you have primary or enteric hyperoxaluria and your kidneys stop working well enough. The body can no longer get rid of the extra oxalate, so the oxalate starts building up. First it builds up in the blood, then in the eyes, bones, skin, muscles, blood vessels, heart and other organs.

Oxalosis can cause many health problems outside the kidneys in its late stages. These include:

• Bone disease.
• Anemia.
• Skin ulcers.
• Heart and eye problems.
• In children, serious problems developing and growing.

You'll likely have a thorough physical exam. You might be asked questions about your health history and eating habits.

Tests to diagnose hyperoxaluria may include:

• Urine tests, to measure oxalate and other substances in the urine. You're given a special container to collect your urine over 24 hours. It's then sent to a lab.
• Blood tests, to check how well your kidneys work and measure oxalate levels in the blood.
• Stone analysis, to find out what kidney stones are made of after you've passed them through urine or gotten them removed with surgery.
• Kidney X-ray, ultrasound or computerized tomography (CT) scan, to check for any kidney stones or calcium oxalate buildup in the body.

You may need more tests to find out for sure if you have hyperoxaluria and see how the disease has affected other parts of your body. These tests may include:

• DNA testing to look for the gene changes that cause primary hyperoxaluria.
• Kidney biopsy to check for buildup of oxalate.
• Echocardiogram, an imaging test that can check for oxalate buildup in the heart.
• Eye exam to check for oxalate deposits in the eyes.
• Bone marrow biopsy to check for buildup of oxalate in the bones.
• Liver biopsy to look for low levels of proteins, also called enzyme deficiencies. This test is needed only in rare cases when genetic testing doesn't show the cause of hyperoxaluria.

If you learn you have primary hyperoxaluria, your siblings also are at risk of the disease. They should have tests as well. If your child has primary hyperoxaluria, you may want to get genetic testing if you and your partner plan to have more children. Medical genetics counselors who have experience with hyperoxaluria can help guide your decisions and testing.

Treatment depends on the type of hyperoxaluria you have, the symptoms and how serious the disease is. How well you respond to treatment also helps your health care team decide how else to manage your condition.

Reducing oxalate

To lower the amount of calcium oxalate crystals that form in your kidneys, your doctor may suggest one or more of these treatments:

• Medicine. Lumasiran (Oxlumo) is a medicine that lowers the level of oxalate in children and adults with primary hyperoxaluria. Prescription doses of vitamin B-6, also called pyridoxine, can help reduce oxalate in the urine in some people with primary hyperoxaluria. Phosphates and citrate prepared by a pharmacy and taken by mouth help keep calcium oxalate crystals from forming.

  Your doctor also may give you other medicines, such as thiazide diuretics. It depends on which other unusual signs are found in your urine. If you have enteric hyperoxaluria, your doctor also may recommend a calcium supplement to take with meals. This could make it easier for oxalate to combine with calcium in the gut and leave the body through stool.

• Drinking lots of fluids. If your kidneys still work well, your doctor will likely tell you to drink more water or other fluids. This flushes the kidneys, prevents oxalate crystal buildup and helps keep kidney stones from forming.
• Diet changes. In general, it's more important to pay attention to your food choices if you have enteric or diet-related hyperoxaluria. Diet changes may help lower the levels of oxalate in your urine. Your health care team may suggest that you restrict foods high in oxalates, limit salt and eat less animal protein and sugar. But diet changes may not help all people with primary hyperoxaluria. Follow your care team's suggestions.

Kidney stone management

Kidney stones are common in people with hyperoxaluria, but they don't always need to be treated. If large kidney stones cause pain or block urine flow, you may need to have them removed or broken up so they can pass in the urine.

Dialysis and transplants

Depending on how serious your hyperoxaluria is, your kidneys may work less well over time. A treatment called dialysis that takes over some of the work of your kidneys may help. But it doesn't keep up with the amount of oxalate your body makes. A kidney transplant or kidney and liver transplant can treat primary hyperoxaluria. A liver transplant is the only treatment that might cure some types of primary hyperoxaluria.

For treatment of kidney stones linked to hyperoxaluria, you may start by seeing your primary care doctor. If you have large, painful kidney stones or stones that are damaging your kidneys, you may get referred to a specialist. This could include a doctor called a urologist, who treats problems in the urinary tract, or a kidney doctor, called a nephrologist.

What you can do

To prepare for your appointment:

• Ask if there's anything you need to do before your appointment, such as limit certain foods or drinks.
• Write down your symptoms, including any that might not seem related to your health problem.
• Keep track of how much you drink and how much urine you pass during a 24-hour period.
• Make a list of all medicines and vitamins or other supplements that you take. Include how much you take, which is called the dose.
• Take a family member or friend along, if possible, to help you remember what you talk about with your doctor.
• Write down questions to ask your doctor.

For hyperoxaluria, some basic questions include:

• What's the likely cause of my symptoms? Are there any other possible causes?
• What kinds of tests might I need?
• Do I have kidney stones? If so, what type are they and how can I prevent them in the future?
• What are the possible treatments that might help me?
• I have other health problems. How can I best manage them together?
• Do I need to plan for follow-up visits?
• Do you have any educational materials that I can take with me? What websites do you suggest?

Feel free to ask any other questions that you think of during your appointment.

What to expect from your doctor

Your doctor may ask questions such as:

• When did you first notice your symptoms?
• Do your symptoms happen all the time or only once in a while?
• How serious are your symptoms?
• Does anything seem to help ease your symptoms?
• Does anything seem to make your symptoms worse?
• Has anyone else in your family had kidney stones?