Kidney function tests are a part of caring for people with kidney disease. They help doctors understand how well your kidneys work and when they need to be monitored more closely.
Most of these tests measure your glomerular filtration rate (GFR), which assesses how well your kidneys filter waste and excess fluid. These tests may also be used to monitor your diabetes or other conditions that affect your kidney function.
Creatinine
The kidneys filter the liquid part of blood through millions of tiny blood vessels called glomeruli. The fluid and waste products that the glomeruli don’t reabsorb are sent out of your body in urine. The rate at which your kidneys filter this fluid is called the glomerular filtration rate (GFR).
Doctors use tests for kidney disease. This creatinine test measures the GFR. They also use a separate test that measures blood urea nitrogen to measure the amount of protein waste the kidneys are excreting. These tests are commonly used together to provide a better overall picture of how well your kidneys are working.
Creatinine is a waste product of muscle breakdown and protein metabolism, and it is produced at a fairly constant rate from one day to the next. It is cleared from the body by the kidneys at a relatively constant rate, so blood creatinine levels are usually a good indicator of how well your kidneys are functioning.
Normal blood creatinine levels vary from 0.7 to 1.3 milligrams per deciliter of blood (mg/dL) for men and 0.6 to 1.1 mg/dL for women. Results may vary slightly depending on age, gender, and body size.
Your kidney function is a key component of your overall health. A healthy kidney can filter out many substances from your body, including proteins, salt and water, excess potassium, and toxins. When your kidneys aren’t working properly, these waste products can build up in the body and eventually cause serious health problems.
Urinary Albumin
Healthy kidneys help your body remove waste products from the blood and regulate the water fluid levels. They also ensure that nutrients and proteins like albumin stay in your blood. When your kidneys are damaged, however, they can’t keep albumin in your blood and start leaking into your urine. This is called albuminuria.
Your healthcare team will usually ask you to give your urine a test that measures the amount of albumin in it. They may use a dipstick, spot urine sample, or 24-hour urine collection. The test can be done in a doctor’s office, health clinic, or hospital.
The laboratory tests can tell your doctor how well your kidneys are working. They can also tell if you have any kidney disease or other health problems that could affect your kidneys.
If you’re being checked for kidney disease, your healthcare team may order a special test to measure how much protein is in your urine. This test can be done with a random urine sample, which is taken after you’ve first urinated in the morning. It’s usually combined with a creatinine test to improve the accuracy of the results.
Your healthcare team will compare the amount of albumin in your urine to a value called the albumin-to-creatinine ratio, or ACR. A level higher than 30 mg/g of albumin-to-creatinine can signify kidney damage.
A normal test result for albumin-to-creatinine should be lower than 60 mg/g of albumin. A value above 300 mg/g indicates early kidney disease.
If you have kidney disease, your healthcare team will prescribe medicines to decrease or stop the loss of albumin in your urine. These medications are called ACEi and ARB, which stand for angiotensin-converting enzyme inhibitors and angiotensin receptor blockers.
You might also be prescribed a medicine to help control your blood pressure. If your blood pressure is high, this medication can help your kidneys eliminate excess water and salt from your body.
GFR
Your kidney function test results tell your doctor how well your kidneys work. They can show whether your kidneys are working normally or if you have kidney disease, which may need to be treated or prevented.
Your GFR, or glomerular filtration rate, measures how well your kidneys filter waste from your blood. It goes down as your kidneys get worse.
A person with a high GFR can usually live without treatment, while someone with a low GFR is more likely to need treatments for kidney problems or a kidney transplant. You may have chronic kidney disease if your GFR is below 60 for three months.
You can find your GFR number by taking a urine sample in a doctor’s office or at home. The test measures how much creatinine is in your urine. Creatinine is a substance your body produces to help supply energy to your muscles, but the more creatinine you have in your blood, the lower your GFR.
The test is done on people of all ages, but it’s more common in adults. It can also be done on children, and it is a good idea to do a test on your kids when you’re testing them for diabetes or other health problems.
It can be challenging to estimate your GFR because it depends on many factors. Besides those mentioned above, it is also affected by age, gender, body size, and diet.
The most accurate way to estimate your GFR is a 24-hour urine collection. It’s not as accurate as a blood test, but it can give you an idea of how well your kidneys are working.
Another type of test is called an eGFR (estimated glomerular filtration rate). It measures how well your kidneys work compared to the average for a person of age, race, and gender.
This type of test is used more often than the 24-hour urine collection because it’s cheaper and easier. However, it can be difficult to accurately estimate your GFR when you have a large muscle mass or your kidneys need to be fixed.
