The kidneys filter waste products, toxins, and excess fluid from the bloodstream. They also play important roles in other essential functions in the body. Without correctly functioning kidneys, the build-up of waste products, fluid, and toxins can negatively affect other organs in the body.
Chronic Kidney Disease (CKD) is a common condition that affects approximately 37 million Americans. This disease is characterized by its progressive nature that is irreversible. Detecting early signs, such as increased protein in the urine or blood, is vital in starting treatment and possibly preventing further damage to the kidneys.
- Blood tests to check kidney function include estimated glomerular filtration rate (eGFR), serum creatinine test, blood urea nitrogen test, and cystatin C test.
- Detecting kidney damage early is vital to help slow disease progression, as nephrologists can implement effective treatment and disease management when kidney damage is minimal.
Why is detecting early signs of kidney disease so vital?
Chronic kidney disease is growing at a significant rate, with 15% or 1 in 7 adults in the U.S. having the disease. In 2020, 130,000 Americans were newly diagnosed with kidney failure, with 9 out of 10 people unaware that they even have kidney disease.
Along with the increased growth of hypertension, type 2 diabetes mellitus, and other risk factors for CKD, it is noticeable that CKD is a worldwide public health problem.
CKD is costly and places a significant burden on healthcare systems, as many patients do not even know they have early-stage CKD until it progresses to kidney failure. By prioritizing early detection and treatment of CKD, the burden and progression may be reduced, and patients may experience improved outcomes.
What Tests are done to Check Kidney Function?
Symptoms of CKD often only begin to present when the kidneys are badly damaged. If CKD is found and treated early, disease progression may be stopped, and other health problems, such as hypertension, heart disease, and diabetes, may be prevented from developing.
The only way to know how well the kidneys are working is through tests:
- Blood tests. Blood tests determine how well the kidneys work and filter the body’s blood. The blood tests used include the Glomerular filtration rate (GFR), serum creatinine, and blood urea nitrogen (BUN).
- Urine tests. Urine tests involve a doctor examining a small amount of urine to check for signs of kidney damage or other health conditions. When the kidneys are damaged, protein may leak into the urine. Urine tests help determine kidney function and the stage of CKD and check for other problems such as urinary tract infection (UTI) or kidney infection.
- Imaging tests. Ultrasounds are used to look at the kidneys and determine if there are problems such as kidney stones, cysts, signs of injury, blood flow to the kidneys, and shape and size. A kidney ultrasound is a non-invasive, safe, and painless test.
- Kidney Biopsy. A kidney biopsy is used to determine the root cause of the kidney problem and what the best treatment option may be. A kidney biopsy is typically ordered when other tests show hematuria, nephrotic syndrome, proteinuria, and kidney disease with no apparent cause.
- Genetic testing. This test can help doctors rule out or confirm if a genetic condition causes kidney disease. It can also help an individual understand their chances of passing on or developing the condition.
What Blood Tests Check for Kidney Function?
Blood tests are significant for checking kidney function, as the kidneys remove waste products, toxins, and extra water from the blood. Thus, blood tests are able to determine how well the kidneys are filtering the body’s blood. The following blood tests are used to check for kidney function:
Estimated Glomerular Filtration Rate (eGFR)
The estimated glomerular filtration rate (eGFR) shows how well the kidneys are removing waste, toxins, and extra fluid from the bloodstream. eGFR is an estimated number that is based on a blood test (creatinine levels) and the individual’s body type, age, and sex.
eGFR is considered one of the most reliable tests to determine how well the kidneys are functioning. For those who are younger than 18, pregnant, obese, or have a high muscle mass, eGFR may not be accurate.
A normal eGFR is 60 or more, up to 90. If eGFR is measured at less than 60 for three months or more, kidney function may be affected.
Serum Creatinine Test
The body’s muscles produce a waste product called creatinine. Healthy kidneys filter creatinine out of the blood so that it can be removed from the body through the urine. When the kidneys are not functioning as they should, creatinine serum levels increase.
This blood test checks to see how much creatinine serum is in the blood. Serum creatinine levels vary based on the person’s amount of muscle, sex, and age. In general, normal serum creatinine levels are 0.7-1.3 mg/dL for males and 0.6-1.1 mg/dL for females.
Blood urine nitrogen (BUN) test
Blood urine nitrogen (BUN) levels are based on a blood test. This test measures the amount of urea nitrogen in the blood. When the body breaks down protein, it produces a waste product called urea nitrogen. Healthy kidneys can remove urea nitrogen from the blood. When the kidneys are damaged, they cannot effectively remove waste products such as urea nitrogen, resulting in increased BUN levels.
A higher-than-normal BUN level may indicate that the kidneys are not working as they should. A doctor or nephrologist will compare BUN results along with other blood test results to decide on the next steps.
Cystatin C Test
Cystatin C is a type of protein made by the cells in the body and is released into the bloodstream at a steady pace. If the kidneys are working correctly, cystatin C is filtered out of the blood, keeping it at a normal level. If cystatin C levels in the blood are too high, the kidneys are not working well enough to filter this protein.
This blood test determines how well the kidneys are working and filtering cystatin C out of the blood. The cystatin C tests are not significantly affected by a person’s gender, muscle mass, or age.
Cystatin C blood tests are helpful if:
- The patient has lost muscle mass or is older, where their creatinine levels vary. A cystatin C test may give doctors a more accurate result than a creatinine test for these patients.
- A previous kidney function test provided unclear results; a cystatin C test can be used to recheck kidney function.
A high level of cystatin C in the bloodstream means that the eGFR may be low, indicating that CKD could develop. High levels of cystatin C may also suggest that there is an increased risk of developing heart disease.
For some individuals, a cystatin C test may not be accurate if they are on steroids or have an untreated thyroid condition.
Panoramic Health is a leading nephrology provider in the United States. We have 16 years of experience managing our patients’ outcomes by leveraging predictive analytics and care management tools. We deliver better outcomes for our patients at a lower cost for everyone.