Introduction: Who Should Undergo Diagnostics

Many people with chronic kidney disease do not feel sick or notice any symptoms in the early stages. This makes diagnostic testing especially important, because it is often the only way to discover that your kidneys are not working as well as they should. The earlier you find out about kidney problems, the more you can do to slow down the damage and protect your health.^[1]

You should consider getting tested if you have certain risk factors that put you at higher risk for kidney disease. The most common risk factors include diabetes and high blood pressure, which together are responsible for most cases of chronic kidney disease. If you have either of these conditions, it is especially important to have your kidney function checked regularly.^[6]

Other reasons to seek kidney testing include having a family history of kidney disease, heart disease, or being older in age. People who have had a kidney injury in the past, such as from an infection or blockage, should also be monitored. If you notice changes in your urine—such as blood, foaming, or a change in how often you go to the bathroom—or if you experience swelling in your ankles, extreme tiredness, confusion, nausea, or itching, these could be signs that your kidneys are not functioning properly.^[5]

Regular testing is particularly important because more than one in seven American adults has chronic kidney disease, and as many as nine out of ten do not know they have it. Early detection through specific blood and urine tests can help catch the disease before it progresses to more serious stages.^[6]

Diagnostic Methods Used to Identify Kidney Disease

Diagnosing kidney disease relies mainly on two types of tests: blood tests and urine tests. These tests measure how well your kidneys are filtering waste and whether they are allowing important substances to leak out. Together, they give doctors a clear picture of your kidney function.^[6]

Blood Tests for Kidney Function

One of the most important blood tests is the serum creatinine test. Creatinine is a waste product that comes from the normal breakdown of muscle tissue. Healthy kidneys filter creatinine out of your blood and remove it through urine. When your kidneys are not working properly, creatinine builds up in your blood. By measuring the level of creatinine, doctors can estimate how well your kidneys are filtering.^[10]

Your creatinine level is used to calculate your estimated glomerular filtration rate, or eGFR. The eGFR is a number that tells doctors how much blood your kidneys can filter each minute. A normal eGFR is above 90. As kidney disease progresses, the eGFR gets lower. This number helps classify kidney disease into five stages, from mild damage in stage 1 to kidney failure in stage 5.^[5]

Another blood test that may be done is the blood urea nitrogen test, or BUN test. Urea nitrogen is another waste product that should be filtered out by healthy kidneys. Like creatinine, high levels of urea nitrogen suggest that your kidneys are not removing wastes efficiently.^[10]

Urine Tests for Kidney Health

Urine tests are equally important in diagnosing kidney disease. One key test is the urinalysis, which checks your urine for abnormalities such as blood, protein, white blood cells, or signs of infection. Finding protein in the urine, a condition called proteinuria, is often an early sign that the kidneys are damaged and leaking substances they should be keeping in the body.^[3]

The urine albumin-to-creatinine ratio, or uACR, is a specific test that measures how much of a protein called albumin is present in your urine compared to creatinine. Albumin should not appear in urine in large amounts if the kidneys are healthy. An elevated uACR indicates kidney damage and can help doctors assess the severity of the disease.^[6]

Imaging and Other Diagnostic Procedures

In some cases, doctors may recommend imaging tests to look at the structure of your kidneys. A kidney ultrasound uses sound waves to create pictures of your kidneys. This test can show whether the kidneys are the right size, whether there are blockages, cysts, or stones, and whether blood flow to the kidneys is normal. Ultrasound is non-invasive and does not involve radiation, making it a safe option for many patients.^[10]

Other imaging tests that might be used include computed tomography, or CT scans, and magnetic resonance imaging, or MRI scans. These provide more detailed images of the kidneys and surrounding structures and can help identify tumors, cysts, or other abnormalities.^[10]

A kidney biopsy is a procedure where a small sample of kidney tissue is removed with a needle and examined under a microscope. This test is usually done when doctors need to find out the exact cause of kidney disease, especially if the diagnosis is unclear or if a specific treatment depends on knowing the type of kidney damage. Although it is more invasive than other tests, a biopsy can provide valuable information.^[10]

How Kidney Disease Is Staged

Once tests are done, doctors use the eGFR and uACR results to stage kidney disease. There are five stages. In stage 1, kidney function is above 90, but there are signs of mild damage such as protein in the urine. In stage 2, eGFR is between 60 and 89, with mild damage. Stage 3 is divided into two parts: stage 3a (eGFR 45-59) and stage 3b (eGFR 30-44), representing moderate loss of function. Stage 4 (eGFR 15-29) indicates severe kidney damage. Stage 5, when eGFR is below 15, is called kidney failure or end-stage kidney disease, where the kidneys are close to stopping completely.^[5]

Understanding these stages helps patients and doctors plan the right treatments and lifestyle changes to slow disease progression and manage symptoms.

Diagnostics for Clinical Trial Qualification

When patients with kidney disease are considered for participation in clinical trials, specific diagnostic tests are used to determine whether they meet the criteria for enrollment. Clinical trials are research studies that test new treatments, medications, or procedures to see if they are safe and effective. These trials often have strict requirements about who can participate, and diagnostic tests help researchers select the right patients.^[9]

The most common tests used for clinical trial qualification are the same blood and urine tests used in standard kidney disease diagnosis: serum creatinine, eGFR, and urine albumin measurements. Researchers use these tests to classify patients by their stage of kidney disease. For example, a trial might only accept patients with stage 3 or stage 4 chronic kidney disease, or it might be focused on people who have very high levels of protein in their urine.^[10]

Some trials may also require additional tests to confirm the specific cause of kidney disease or to rule out other conditions. For instance, if a trial is testing a treatment for a rare kidney disease such as IgA nephropathy or lupus nephritis, a kidney biopsy may be required to confirm the diagnosis before a patient can enroll. Blood tests to check for inflammation, immune system activity, or specific antibodies might also be needed.^[9]

Imaging studies such as ultrasound or CT scans may be part of the screening process to ensure that the kidneys have a certain size or structure, or to exclude conditions like kidney stones or tumors that would make a patient ineligible for the study.^[10]

Clinical trials may also monitor patients closely during the study using the same diagnostic tests to see if the treatment is working or if there are any side effects. Regular blood and urine tests, along with blood pressure measurements and other health checks, help researchers and doctors track how the kidneys are responding over time.^[9]