Chronic kidney disease (CKD) is defined as abnormal kidney structure or function lasting more than three months. The diagnosis hinges on two key measurements: how well your kidneys filter blood (estimated by a number called eGFR) and whether protein is leaking into your urine. About 35.5 million U.S. adults, roughly 1 in 7, have CKD, and as many as 9 in 10 of them don’t know it.
How CKD Is Diagnosed
Two simple tests form the backbone of a CKD diagnosis. The first is a blood test that measures creatinine, a waste product your muscles produce at a steady rate. Your creatinine level, combined with your age and sex, is used to calculate your estimated glomerular filtration rate (eGFR), a number that represents how efficiently your kidneys are filtering. A normal eGFR is around 100, though it naturally decreases with age even in healthy people. An eGFR below 60 on two separate tests taken at least 90 days apart meets the threshold for CKD.
The second test is a urine sample that checks for albumin, a protein that healthy kidneys keep in the blood. The result is reported as a urine albumin-to-creatinine ratio (uACR). A result of 30 or above may indicate kidney damage. If either an eGFR below 60 or a uACR above 30 persists for more than three months, that’s CKD by the current international definition.
You can also be diagnosed with CKD even if your eGFR is above 60, as long as there’s other evidence of kidney damage lasting more than three months. That evidence could include blood in the urine from a kidney source, structural problems visible on imaging (such as polycystic kidneys), electrolyte imbalances caused by kidney tubule disorders, abnormal findings on a kidney biopsy, or a history of kidney transplantation.
The Five Stages of CKD
CKD is classified into five stages based on eGFR, with stage 1 being the mildest and stage 5 representing kidney failure. The stages break down like this:
- Stage 1 (eGFR 90 or above): Kidney function is normal, but there’s evidence of damage such as protein in the urine or a structural abnormality.
- Stage 2 (eGFR 60–89): Mild loss of function with markers of kidney damage.
- Stage 3a (eGFR 45–59): Mild to moderate loss of function.
- Stage 3b (eGFR 30–44): Moderate to severe loss of function.
- Stage 4 (eGFR 15–29): Severe loss of function.
- Stage 5 (eGFR below 15): Kidney failure, often requiring dialysis or transplant.
Staging doesn’t stop at eGFR. Doctors also classify how much protein is leaking into urine using three albuminuria categories: A1 (less than 30 mg/g, normal to mildly increased), A2 (30–300 mg/g, moderately increased), and A3 (above 300 mg/g, severely increased). Someone with a higher eGFR but heavy protein loss can face a worse prognosis than someone with a lower eGFR and no protein leakage. The combination of these two numbers determines your overall risk category, ranging from low to very high, for heart disease and further kidney decline.
What Causes It
The two most common causes of CKD in adults are diabetes and high blood pressure. Diabetes damages the tiny blood vessels inside the kidneys over time, reducing their filtering ability. High blood pressure does something similar, putting excess strain on those same vessels until they stiffen and narrow. Together, these two conditions account for the majority of CKD cases.
Other causes include autoimmune diseases like lupus, inherited conditions such as polycystic kidney disease, recurrent kidney infections, obstruction from kidney stones or an enlarged prostate, and prolonged use of certain medications that are hard on the kidneys. Sometimes the cause is never clearly identified, particularly in older adults whose kidney function has declined gradually.
Why Most People Don’t Notice Early Symptoms
Most people in the early stages of CKD feel completely normal. There’s no pain, no obvious sign that anything is wrong. For many people, the only way to catch it is through routine blood and urine tests, which is why screening matters if you have diabetes, high blood pressure, or a family history of kidney disease.
Some people develop swelling (edema) in the legs, feet, or ankles when the kidneys can’t clear extra fluid and salt. This is more common in advanced disease or when a large amount of protein is leaking into the urine. But for stages 1 through 3, most people are symptom-free.
Symptoms of Advanced CKD
As kidney function drops further, particularly in stages 4 and 5, the body starts to feel the effects of waste buildup. Symptoms at this point can include loss of appetite, nausea, persistent fatigue, trouble concentrating, and difficulty sleeping. Some people notice they urinate more or less often than usual, or that their urine looks foamy. Itching, dry skin, darkened skin, numbness, and unexplained weight loss can all develop. Muscle cramps, chest pain, and shortness of breath are signs that kidney function has declined significantly.
These symptoms tend to creep in gradually, which is part of why CKD so often goes undetected. People attribute the fatigue to aging or stress. The itching gets chalked up to dry weather. By the time the symptoms are unmistakable, kidney function may already be severely reduced.
How Risk Is Assessed
Doctors use a color-coded risk matrix, sometimes called a heat map, that plots your eGFR stage against your albuminuria category. The result is one of four risk levels: low, moderately increased, high, or very high. This combined score guides how often you need monitoring and whether you should see a kidney specialist.
For example, someone in stage 3a with normal protein levels (A1) falls into a moderately increased risk category and typically gets monitored once or twice a year. Someone in stage 3a with heavy protein loss (A3) jumps to very high risk and needs closer follow-up. The key takeaway is that eGFR alone doesn’t tell the full story. The amount of protein in your urine is just as important for predicting how CKD will progress and whether it raises your risk of heart problems.
Who Should Get Tested
Because CKD is silent in its early stages and 9 out of 10 people who have it are unaware, testing is the only reliable way to catch it early. The two core tests, a blood draw for creatinine (to calculate eGFR) and a urine sample for albumin, are inexpensive and widely available. Creatinine levels above roughly 1.2 for women or 1.4 for men can be a flag, though the eGFR calculation gives a more complete picture.
If you have diabetes, high blood pressure, heart disease, a family history of kidney disease, or are over 60, regular kidney screening is particularly important. Early detection gives you the best chance of slowing progression through blood pressure control, blood sugar management, dietary adjustments, and medications that protect kidney function.