Introduction: Who Should Be Tested for Chronic Kidney Disease

Chronic kidney disease often develops silently, without causing any noticeable symptoms in its early stages. This makes it particularly important to know when diagnostic testing is advisable. Many people discover they have kidney problems only after routine blood or urine tests reveal something unusual, sometimes during check-ups for completely different health concerns.^[1]

You should consider seeking diagnostic tests if you belong to certain groups that face higher risk. People with diabetes—a condition where the body struggles to control blood sugar levels—are especially vulnerable, as are those with high blood pressure, which puts strain on the small blood vessels in the kidneys over time. If you have heart disease, a family history of kidney problems, or if you’re 60 years or older, regular screening becomes particularly important.^[2][5]

Other situations that warrant diagnostic attention include a history of acute kidney injury—a sudden loss of kidney function—previous episodes of kidney infections, or a history of preeclampsia during pregnancy. People who are Black or of South Asian origin also face higher risk and may benefit from earlier and more regular testing, as chronic kidney disease affects these communities more frequently.^[3][6]

Because early-stage chronic kidney disease rarely causes symptoms, waiting until you feel unwell is not a safe strategy. Testing may be the only way to discover kidney disease before it progresses. The sooner you know about kidney problems, the sooner you can start taking steps to protect your remaining kidney function and prevent complications.^[7]

Diagnostic Methods for Identifying Chronic Kidney Disease

When doctors suspect kidney disease or screen someone at risk, they rely on several key diagnostic approaches. Understanding these methods can help remove some of the anxiety around testing and make the process feel less mysterious.

Blood Tests to Measure Kidney Function

The cornerstone of kidney disease diagnosis involves blood tests that measure how well your kidneys are filtering waste from your bloodstream. The most important measurement is called the estimated glomerular filtration rate, or eGFR, which indicates how much blood your kidneys filter each minute. This number is calculated using a blood test that measures creatinine—a waste product that builds up when kidneys aren’t working properly.^[3][4]

Your eGFR result is expressed as a number in milliliters per minute. A healthy kidney function typically shows an eGFR of 90 or higher. As the number decreases, it indicates worsening kidney function. For example, an eGFR between 60 and 89 suggests mild kidney damage, while numbers below 60 indicate more significant problems. An eGFR below 15 means your kidneys are close to failure or have already stopped working effectively.^[3][12]

The calculation of eGFR has evolved over time. Healthcare providers now use an equation called the CKD-EPI creatinine equation, which has been updated to exclude race as a variable. This change reflects ongoing efforts to ensure more accurate and equitable diagnosis across all populations.^[4][17]

In some cases, doctors may order an additional blood test to measure cystatin C, another waste product in the blood. This test can help confirm eGFR results, especially when there’s uncertainty about the diagnosis or when creatinine levels might be affected by factors like muscle mass or diet.^[4][17]

Urine Tests to Detect Kidney Damage

While blood tests show how well your kidneys are filtering, urine tests reveal whether the filtering system is damaged and leaking things it shouldn’t. The most common urine test looks for albumin, a type of protein that healthy kidneys keep in the bloodstream. When albumin appears in urine, it signals that the kidney’s filtering units are damaged.^[4][15]

This test is called the albumin-to-creatinine ratio, or ACR, and it’s typically done on a small sample of your first morning urine, though it can be collected at any time. Doctors use a “spot” urine sample, meaning you don’t need to collect urine over 24 hours. First morning samples tend to be more reliable because they’re more concentrated and provide consistent results.^[4]

The ACR result tells doctors how much albumin is leaking into your urine compared to creatinine. Normal results show less than 30 milligrams of albumin per gram of creatinine. Amounts between 30 and 300 indicate moderate kidney damage, while levels above 300 suggest severe damage. This measurement helps stage the disease and monitor its progression over time.^[4]

Sometimes doctors order a general urinalysis, which examines urine for various abnormalities including protein, blood, white blood cells, or signs of infection. This broader test can reveal other kidney problems beyond chronic kidney disease and help distinguish between different types of kidney conditions.^[15]

Imaging Studies to Examine Kidney Structure

When blood and urine tests suggest kidney disease, or when doctors need to understand the cause of kidney problems, they may order imaging tests to look at the kidneys’ structure. These tests don’t measure function, but they reveal physical abnormalities that might explain why the kidneys aren’t working properly.

Ultrasound is the most common imaging test for kidneys because it’s safe, non-invasive, and doesn’t expose you to radiation. During an ultrasound, a technician places a device called a transducer on your back or abdomen, which sends sound waves through your body. These waves bounce off your kidneys and create real-time images on a screen. Ultrasound can show if your kidneys are the right size, detect blockages, identify cysts or tumors, and reveal structural abnormalities.^[4]

Other imaging options include computed tomography, or CT scans, which use X-rays to create detailed cross-sectional images of the kidneys. CT scans provide more detail than ultrasound but involve radiation exposure. They’re particularly useful for detecting kidney stones, tumors, or structural problems that might be harder to see on ultrasound.^[11]

In some situations, doctors might order a kidney biopsy, which involves removing a tiny piece of kidney tissue with a needle for examination under a microscope. This isn’t a routine test but becomes necessary when doctors need to identify the specific type of kidney disease, especially when the cause isn’t clear from other tests. The biopsy can reveal patterns of damage that point to particular diseases like glomerulonephritis or other conditions affecting the kidney’s filtering units.^[4]

Staging and Classification

Once diagnostic tests confirm chronic kidney disease, doctors use a staging system to describe how advanced the condition is. This classification helps guide treatment decisions and predict future health risks. The system has five main stages based on your eGFR, running from Stage 1, where kidneys still work well but show signs of damage, to Stage 5, where kidneys have failed or are very close to failing.^[3][4]

The staging system also incorporates the level of protein in your urine, creating subcategories that provide a more complete picture. For example, Stage 3 is divided into 3a and 3b depending on whether your eGFR is 45-59 or 30-44. This matters because Stage 3a often represents mild to moderate damage where many people can maintain stable kidney function with proper care, while Stage 3b indicates more serious damage requiring closer monitoring.^[3][12]

Modern classification systems also identify the underlying cause of kidney disease whenever possible, whether it’s diabetes, high blood pressure, autoimmune conditions, or other factors. Understanding the cause helps doctors tailor treatment to address not just the kidney damage but also the condition driving it forward.^[4]

Diagnostic Testing for Clinical Trial Participation

When people with chronic kidney disease consider participating in clinical trials—research studies testing new treatments—they undergo additional diagnostic evaluations beyond standard care. These tests serve as entry criteria to ensure participants meet specific requirements and to establish baseline measurements for comparison as the trial progresses.

Clinical trials typically require precise documentation of kidney function using the same diagnostic tests used in regular care: eGFR calculations based on serum creatinine levels, and albumin-to-creatinine ratio measurements from urine samples. However, trials often set specific numeric thresholds for participation. For instance, a trial might only accept participants with eGFR between certain values, such as 30 to 60 mL/min, to study people at a particular disease stage.^[4][15]

Many trials require confirmation testing, meaning you need at least two separate measurements taken weeks or months apart showing consistent results. This confirms that your kidney function truly represents chronic disease rather than temporary changes. The three-month rule for diagnosing chronic kidney disease often applies to trial eligibility as well—your condition must be documented as lasting at least that long.^[4]

Some clinical trials investigating new kidney disease treatments may use additional or more frequent testing than you’d receive in standard care. This might include more regular blood draws to monitor eGFR changes over time, repeated urine collections to track protein levels, or periodic imaging studies to assess kidney structure. Trials studying specific types of kidney disease, such as those caused by diabetes or high blood pressure, typically require documented evidence of these underlying conditions as well.^[4]

The use of cystatin C testing has become more common in clinical trials because it provides an additional way to estimate kidney function that may be more accurate in certain populations. Some trials use cystatin C-based eGFR calculations either alone or combined with creatinine-based calculations to qualify participants and monitor outcomes.^[4][17]

Blood pressure measurements also play an important role in trial qualification, as high blood pressure both causes and results from kidney disease. Trials may require documentation that your blood pressure is either above certain levels, indicating active disease, or below certain thresholds, indicating that other treatments have brought it under control before testing a new intervention.^[11][17]

For people with diabetes and kidney disease, clinical trials often require hemoglobin A1C testing to measure blood sugar control over the previous three months. This test helps ensure that participants have similar levels of diabetes management, which is important because blood sugar control affects kidney disease progression. Trials testing diabetes medications that might protect kidneys typically include A1C requirements in their eligibility criteria.^[22]

Some specialized trials may require kidney biopsies to confirm the exact type of kidney disease at the microscopic level. While not common for all chronic kidney disease trials, studies focusing on specific conditions like glomerulonephritis or other rare kidney diseases often need this definitive diagnosis before enrollment. The biopsy results become part of the baseline data used to evaluate whether the experimental treatment works.^[4]