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Diabetes is a long-term (chronic) health condition where your blood sugar is too high. People with diabetes either don’t make insulin, the hormone that regulates blood sugar, or don’t use insulin effectively.

Diabetes increases the risk of certain other health conditions, including kidney disease. In fact, according to the National Institute of Diabetes and Digestive and Kidney Diseases, 1 in 3 adults with diabetes has kidney disease.

Glomerular filtration rate is a test that’s important in the diagnosis and monitoring of kidney disease. Keep reading to learn more about this test, what the results mean, and how it plays a role in diabetic kidney disease.

Your kidneys work to filter waste products and excess fluids from your blood, which are then released from your body as urine.

A glomerular filtration rate (GFR) test measures how well your kidneys are carrying out their filtration function. This test usually involves testing your blood for a waste product called creatinine.

Because early kidney disease often has no symptoms, a GFR test is a valuable tool for monitoring kidney function. This is particularly important if you‘re at an increased risk of kidney disease, especially if you have diabetes.

What happens during a GFR test?

To test your GFR, your doctor will refer you for a blood test.

When you get a blood test, a medical professional will use a small needle to draw your blood, usually from a vein in your arm. The blood sample is then sent to a laboratory for testing.

A technician at the testing lab will test your blood sample to find out how much creatinine is in your blood.

Things get a little more complex from here. Your creatinine level can provide information about your kidney function, but it isn‘t the same thing as your GFR. So, to find out your GFR, your creatinine test results are plugged into a math formula with other variables like your age and sex. This step is usually completed by a technician at the testing lab or by your doctor.

The result is known as your estimated GFR, or eGFR.

How should I prepare for a GFR test?

Your doctor will give you instructions on how to prepare for your GFR test. If you aren‘t sure, it‘s best to ask your doctor.

It’s possible that your doctor will ask you to fast for a specific period of time before your blood test, especially if you’re having additional tests that require fasting. This often means drinking only water and eating no food. You might also be asked to avoid specific foods before the test.

To get a more accurate result, it’s important to follow your doctor’s instructions.

Estimated glomerular filtration rate

Because testing GFR can be very complex, it’s often estimated. You may see this called an estimated glomerular filtration rate (eGFR) test.

eGFR uses the results from a blood test for creatinine, a waste product produced by your muscles. While creatinine production can vary by individual, high levels in the blood can potentially indicate decreased kidney function.

Once the result of the creatinine test is obtained, a lab technician or doctor will calculate your eGFR. Your eGFR is an estimate of your kidney function that’s also based on information like your age and sex.

In the United States, a different version of the formula is generally used when calculating eGFR test results for Black people. However, this modified test, known as the race-adjusted eGFR, has been criticized for lacking a sound scientific basis. Many experts now suggest that the use of race-adjusted eGFR tests may be contributing to health inequities for Black people.

Because eGFR is one of the major tools that a doctor can use to assess kidney function, researchers are working to develop eGFR tests that are inclusive and unbiased. Newer eGFR tests that include both creatinine and a protein called cystatin C may be more accurate, according to 2021 research.

The creatinine-based eGFR test is not recommended for people with certain conditions that can affect the accuracy of the results. These conditions include:

In these cases, a doctor may opt to use other tests to assess your kidney function.

For most adults, a GFR of over 90 is considered normal. However, a GFR of 60 or higher is also considered within the normal range if you do not have other signs of kidney disease.

A GFR lower than 60 may be an indication that you have kidney disease.

When GFR falls to 15 or lower, it can be a sign that you have kidney failure.

GFR measurements can vary by age. As you get older, GFR naturally decreases.

Average glomerular filtration rate by age

According to the National Kidney Foundation, the average GFR results by age are as follows:

  • Ages 20 to 29: 116
  • Ages 30 to 39: 107
  • Ages 40 to 49: 99
  • Ages 50 to 59: 93
  • Ages 60 to 69: 85
  • Ages 70 and older: 75

If your GFR is below 60, it may be a sign of kidney disease, which means your kidney function may be impaired. You’re not likely to notice other symptoms in the early stages of kidney disease, so getting tested is important if you’re at an increased risk.

In later stages, the symptoms of kidney disease can include:

A GFR of 15 or lower is a sign of kidney failure. This is when your kidneys stop being able to effectively filter wastes and extra fluids from your blood. People with kidney failure need dialysis or a kidney transplant to survive.

It’s also possible for GFR to be very high in some people. This is called glomerular hyperfiltration. In some people with glomerular hyperfiltration, GFR can go as high as 180.

Glomerular hyperfiltration can happen in the early stages of diabetes. Although additional research is needed to fully understand the significance of glomerular hyperfiltration, it’s believed to be associated with an increased risk of kidney damage.

Can low GFR be reversed?

If diabetic kidney disease is causing you to have low GFR, it’s important to take steps to keep your kidneys as healthy as possible.

A 2013 study suggests that a small proportion of people with kidney disease — around 15 percent — may be able to improve their GFR results over time. But even if you can’t always increase your GFR, you can help slow the progression of kidney disease and keep GFR from falling lower.

Steps you can take include:

  • managing your diabetes to keep blood sugar at target levels
  • preventing or treating high blood pressure
  • eating a diet high in fresh vegetables and low in processed foods and salt
  • getting regular, moderate exercise

Before making any major changes to your lifestyle, be sure to talk with your doctor.

Diabetic kidney disease can happen in both type 1 and type 2 diabetes. However, it’s more common in type 2 diabetes.

According to 2015 research, about half of people with type 2 diabetes develop diabetic kidney disease, compared with about one-third of people with type 1 diabetes.

With diabetes, high blood sugar causes damage to small blood vessels throughout your body, including in your kidneys. Your kidneys filter wastes and extra fluids from your body by passing blood through bundles of tiny blood vessels. Each bundle is called a glomerulus, and your kidneys contain millions of them.

When blood vessels in the kidneys are damaged, they don’t filter wastes and extra fluids effectively. A blood protein called albumin may be detectable in the urine at this point. Along with low GFR, albumin in your urine can be a sign of kidney disease.

Additionally, many people with diabetes develop high blood pressure. By itself, high blood pressure is also a risk factor for kidney disease, as it can damage your kidneys.

In addition to high blood pressure, other factors that may increase your risk of diabetic kidney disease include:

  • not following your diabetes treatment plan
  • older age
  • having diabetes for a longer time
  • smoking
  • having overweight or obesity
  • being physically inactive
  • heart disease
  • family history of kidney disease

If the cost of managing diabetes is a concern for you, consider looking into potential options to reduce the costs.

Rates of kidney disease are higher among some racial and ethnic groups. This includes people who are:

  • Black
  • Hispanic or Latino
  • Asian American or Pacific Islander
  • American Indian or Alaska Native

A range of experts, including a task force of the National Kidney Foundation and American Society of Nephrology, have identified racism and inequities in healthcare as factors that help explain the increased risk.

If you have diabetes, there are several steps you can take to help lower your risk of diabetic kidney disease. Let’s look at each of these factors:

  • Stick to your treatment plan. To reduce the risk of diabetes complications like diabetic kidney disease, it’s vitally important to follow the diabetes treatment plan developed by your doctor. This includes:
    • testing A1C regularly, as recommended by your doctor
    • seeing your doctor if you have consistently high blood sugar readings
  • Treat high blood pressure. Because high blood pressure increases the risk of kidney disease, it’s important to monitor your blood pressure. If you have high blood pressure, your doctor can prescribe medications to help manage it.
  • Address high cholesterol. Having high cholesterol can contribute to heart disease and cause further damage to blood vessels. If you have high cholesterol, it can be managed using medications called statins.
  • Try to quit smoking. Smoking also increases your risk of kidney disease. If you smoke, consider talking with your doctor about developing a plan to quit.
  • Manage weight. If overweight or obesity is a concern for you, ask your doctor about healthy ways to lose weight.
  • Get regular exercise. Regular exercise is good for both your physical and mental health. It can also help lower blood pressure and aid in weight management.
  • Drink alcohol in moderation or not at all. Drinking too much alcohol can be hard on both your liver and your kidneys. It may also increase your blood pressure. If you drink alcohol, be sure to do so in moderation.
  • Avoid certain medications. Some medications, such as nonsteroidal anti-inflammatory drugs (NSAIDs) like ibuprofen and naproxen can lead to kidney damage. Ask your doctor about which medications to avoid and which ones are safe for you to take.
Screening for kidney disease

If you have diabetes, your doctor will screen you for kidney disease each year by measuring GFR and urine albumin levels. This yearly screening can help detect kidney disease early and prevent additional damage from occurring.

If you have diabetes and kidney disease, it’s important to know that you aren’t alone. There are many places to find resources and support, such as:

You can also find diabetes resources within the Healthline community. This includes:

Additionally, you can find more information about kidney disease by checking out the websites for the National Kidney Foundation or the American Kidney Fund.

People with diabetes are at an increased risk of developing kidney disease. By taking steps to manage your diabetes and live a health-promoting lifestyle, you can reduce your risk.

A GFR test is one way for your doctor to assess your kidney function. Having a lower-than-normal GFR can indicate kidney disease or even kidney failure.

If you have diabetes, your doctor will check your kidney function yearly by testing and measuring your GFR and urine albumin levels. To lower your risk of diabetic kidney disease, it’s most important to:

  • follow your diabetes treatment plan carefully
  • manage your blood pressure

If you’ve already been diagnosed with diabetic kidney disease, these same steps can help slow the progression of the disease.