Introduction: Who Should Undergo Diagnostics and When

If you have diabetes or high blood pressure, or if kidney disease runs in your family, you should talk to your doctor about getting tested for kidney problems. These conditions are the most common causes of kidney damage, and catching issues early can help protect your kidney function for years to come.^[1] Many people don’t realize that kidney disease often develops silently, without causing any noticeable symptoms until the damage is quite advanced.^[2]

You should consider seeking diagnostic testing if you are at higher risk for kidney disease. This includes people with diabetes, those with high blood pressure, individuals with heart disease, or anyone with a family history of kidney failure.^[8] Your age matters too—older adults are at greater risk. If you belong to certain racial or ethnic groups, particularly if you are Black or of South Asian origin, you face a higher chance of developing chronic kidney disease.^[7]

It’s important to get tested even if you feel completely fine. In the early stages of kidney disease, you might not experience any symptoms at all. The kidneys can lose a significant amount of their function before you notice anything wrong.^[1] This is why regular screening is so crucial for people in high-risk groups. Your doctor may recommend testing as part of routine health checks if you have diabetes or high blood pressure.

Sometimes, symptoms do appear that should prompt you to see a doctor right away. If you notice you’re making much less urine than usual, if you develop swelling around your hands, ankles, or face, or if you experience extreme tiredness, confusion, nausea, or changes in how often you need to go to the bathroom, you should seek medical attention urgently.^[1][3] These could be signs that your kidneys are struggling to do their job properly.

If you have diabetes, it’s especially important to stay in your target blood sugar range and get regular kidney function checks. Diabetes is one of the leading causes of kidney disease, and unmanaged blood sugar levels over time can damage the tiny filters in your kidneys.^[2] Similarly, if you have high blood pressure, keeping your blood pressure controlled and monitored can prevent strain on your kidneys’ blood vessels.^[7]

Diagnostic Methods: Classic Tests to Identify Kidney Disease

Doctors use several different tests to check how well your kidneys are working and whether they show any signs of damage. These tests measure various substances in your blood and urine that indicate kidney function. Understanding what each test does can help you feel more prepared when your doctor orders them.

Blood Tests for Kidney Function

One of the most important blood tests is called estimated glomerular filtration rate, or eGFR for short. This test calculates how well your kidneys are filtering waste from your blood.^[1] Your kidneys contain millions of tiny filters called glomeruli, and the eGFR tells doctors how much blood these filters can clean each minute. A normal eGFR is above 90. When the number drops below 60, it suggests your kidneys aren’t working as well as they should.^[1]

The eGFR calculation uses a blood test that measures creatinine. Creatinine is a waste product that comes from normal muscle activity, and healthy kidneys remove it from your blood. When your kidneys aren’t working properly, creatinine builds up in your bloodstream.^[10] Doctors use your creatinine level, along with your age, sex, and sometimes race, to calculate your eGFR.

Chronic kidney disease is classified into five stages based on your eGFR results. In Stage 1, your eGFR is higher than 90, which means your kidneys have only mild damage but still function normally. In Stage 2, your eGFR may be between 60 and 89, showing more damage but still good function. Stage 3 is split into two parts—Stage 3a with eGFR between 45 and 59, and Stage 3b with eGFR between 30 and 44. At Stage 4, your eGFR is between 15 and 29, indicating severe loss of kidney function. Stage 5 means your eGFR is below 15, and your kidneys are nearing or at complete failure.^[1]

Another blood test measures blood urea nitrogen, or BUN. Urea nitrogen is another waste product that healthy kidneys remove from your blood. Like creatinine, high levels of BUN can indicate that your kidneys aren’t filtering properly.^[10]

Urine Tests

Urine tests are just as important as blood tests for diagnosing kidney disease. One key test measures protein in your urine, a condition called proteinuria. Normally, your kidneys keep protein in your blood where it belongs, but when the kidney filters are damaged, protein can leak into your urine.^[11] Finding protein in your urine is often one of the earliest signs of kidney damage.

The most common urine test is the albumin-to-creatinine ratio, or ACR. Albumin is a specific type of protein, and this test measures how much albumin is in a small sample of your urine compared to creatinine. Doctors often use an early morning “spot” urine sample for this test.^[10] The 2012 kidney disease classification guidelines include staging based on three levels of how much albumin is in your urine—A1, A2, and A3—with higher numbers indicating more protein leakage.^[10]

A simple urinalysis can also provide important information. This basic test examines your urine for blood, protein, and other abnormalities that might suggest kidney problems or other conditions affecting your urinary system.^[3]

Imaging Tests

Sometimes doctors need to see a picture of your kidneys to understand what’s going on. Ultrasound is a common imaging test that uses sound waves to create images of your kidneys. It’s painless and doesn’t use radiation. An ultrasound can show the size and shape of your kidneys and detect problems like kidney stones, cysts, or blockages.^[11]

Other imaging tests include CT scans and MRI scans, which can provide more detailed pictures of your kidneys and surrounding structures. These might be used if your doctor needs to investigate specific problems or plan treatment.^[11]

Specialized Tests

For patients with renal insufficiency due to problems with blood flow to the kidneys, doctors may use specialized tests. Duplex ultrasound scanning can diagnose renal artery disease, which occurs when the arteries supplying blood to the kidneys become narrowed.^[9] Other non-invasive tests include CT angiography and MR angiography. In some cases, doctors may perform contrast angiography, which involves injecting a special dye to see the blood vessels clearly.^[9]

If your doctors need to determine the exact cause of kidney damage or how severe it is, they might recommend a kidney biopsy. This procedure involves taking a tiny sample of kidney tissue, which is then examined under a microscope. A biopsy can reveal specific diseases affecting the kidneys and help guide treatment decisions.^[11]

Diagnostics for Clinical Trial Qualification

When researchers study new treatments for kidney disease in clinical trials, they need to make sure participants meet specific criteria. The tests used to qualify patients for clinical trials are often similar to the standard diagnostic tests, but they may be applied with stricter criteria or combined in specific ways to identify the right participants.

Clinical trials typically require confirmation that participants have chronic kidney disease at a certain stage. This means researchers will use blood tests to measure eGFR and determine which stage of kidney disease someone has. Most trials specify a range of eGFR values for enrollment—for example, a trial might only include people with Stage 3 or Stage 4 chronic kidney disease, meaning their eGFR is between 15 and 59.^[10]

Urine tests measuring albumin levels are also standard for qualifying patients for kidney disease clinical trials. Researchers often look for specific amounts of protein in the urine to ensure participants have the type and severity of kidney damage the study is designed to investigate. The albumin-to-creatinine ratio helps classify patients according to how much kidney damage they have.^[10]

Some clinical trials focus on specific causes of kidney disease. For these studies, doctors might need additional tests to confirm the underlying cause before someone can participate. For example, if a trial is testing a treatment for diabetic kidney disease, participants would need documentation of diabetes along with evidence of kidney damage. If the trial focuses on kidney disease caused by high blood pressure, confirmation of hypertension would be necessary.^[1][2]

Blood pressure measurements are often part of clinical trial screening because high blood pressure is both a cause and a complication of kidney disease. Trials may require that participants have blood pressure within certain ranges, either controlled or uncontrolled, depending on what the study is testing.^[8]

Clinical trials may also require baseline tests to measure complications related to kidney disease. This could include tests for anemia (checking red blood cell counts), tests for bone health (measuring calcium, phosphorus, and parathyroid hormone levels), or tests for heart disease (such as electrocardiograms or cholesterol levels). These measurements help researchers understand each participant’s overall health status and track how the treatment affects different aspects of their condition.^[10]

Before joining a clinical trial, participants typically undergo comprehensive screening that includes a review of their medical history, a physical examination, and multiple blood and urine tests. Some trials may also require imaging studies like ultrasounds or kidney biopsies to confirm the diagnosis and assess the severity of kidney damage.^[11] These thorough assessments ensure that each person enrolled in the trial is appropriate for the study and can be safely monitored throughout the research period.