Chronic kidney disease (CKD) is classified into five stages based on how well your kidneys filter waste from your blood. That filtering capacity is measured by a number called the estimated glomerular filtration rate, or eGFR, which represents how many milliliters of blood your kidneys can clean per minute. About 14% of adults worldwide are living with some stage of CKD, and most of them don’t know it because the early stages rarely cause symptoms.
How Kidney Disease Is Diagnosed
A single low eGFR reading isn’t enough for a diagnosis. CKD is officially defined as either an eGFR below 60 or the presence of kidney damage markers, such as protein in the urine, that persist for at least three months. That three-month threshold matters because temporary drops in kidney function can happen during infections, dehydration, or acute illness and then resolve on their own.
Your eGFR is calculated from a simple blood test that measures creatinine, a waste product your muscles produce at a steady rate. The current standard formula, updated in 2021, uses your creatinine level, age, and sex. An older version included a race-based adjustment, but that was removed after the National Kidney Foundation and the American Society of Nephrology determined it wasn’t necessary and could create disparities in care. For borderline results, a second blood marker called cystatin C can be added to improve accuracy, especially in people whose creatinine levels might be unreliable (such as those with very high or very low muscle mass).
Stage 1: Normal Filtration With Kidney Damage
In stage 1, your eGFR is 90 or above, which is technically in the normal range. The reason it still counts as kidney disease is that there’s evidence of structural or functional damage, usually detected as protein leaking into your urine (albuminuria) or visible abnormalities on imaging. You won’t feel any different at this stage. Most people discover it incidentally through routine blood work or urine tests done for another reason, like managing diabetes or high blood pressure.
Stage 2: Mildly Decreased Function
Stage 2 corresponds to an eGFR between 60 and 89. Like stage 1, it requires evidence of kidney damage beyond the eGFR number alone, because mild declines in filtration can be a normal part of aging. There are still no noticeable symptoms. The practical significance of a stage 2 diagnosis is that it flags you for closer monitoring. Managing blood pressure and blood sugar, if you have diabetes, becomes especially important here because these are the two biggest drivers of progression.
Stage 3: Where Most People Get Diagnosed
Stage 3 is split into two substages. Stage 3a means your eGFR is between 45 and 59, representing a mild-to-moderate drop in function. Stage 3b means your eGFR has fallen to 30-44, a moderate-to-severe decline. This is the stage where CKD is most commonly caught, because an eGFR below 60 on its own, confirmed over three months, meets the diagnostic threshold even without other markers of damage.
Most people in stage 3 still feel fine. Some may begin to notice subtle changes like fatigue or mild swelling in the ankles, but these are easy to attribute to other causes. The real concern at this stage is what’s happening beneath the surface: your kidneys are starting to struggle with their secondary jobs, like activating vitamin D, balancing minerals, and clearing phosphorus from your blood. These hidden imbalances can quietly weaken your bones and stiffen your blood vessels long before you feel anything wrong.
Stage 4: Severe Decline
At stage 4, your eGFR is between 15 and 29. This is the point where symptoms typically become hard to ignore. Waste products and fluid are building up faster than your kidneys can handle, which can cause nausea, loss of appetite, persistent fatigue, trouble sleeping, and difficulty concentrating. Fluid retention may lead to swelling in your legs, shortness of breath, or blood pressure that becomes increasingly difficult to control even with medication.
Stage 4 is also when planning for the future becomes urgent. If your eGFR drops below 20, you can be evaluated and placed on the waiting list for a kidney transplant. Conversations about dialysis typically begin here as well, so that if and when it becomes necessary, the transition isn’t rushed.
Stage 5: Kidney Failure
Stage 5, sometimes called end-stage kidney disease, means your eGFR has fallen below 15. Your kidneys are functioning at less than 15% of their normal capacity. At this point, the buildup of toxins in your blood can cause severe nausea and vomiting, mental fog, personality changes, dangerous rises in potassium levels that can affect your heart rhythm, and inflammation of the membrane surrounding the heart.
The decision to start dialysis is not triggered by hitting a specific number. It’s based on whether your symptoms are consistent with advanced kidney failure and whether dialysis is likely to relieve them. Some people with an eGFR below 15 manage for a time without dialysis, while others need it sooner. The two main options at this stage are dialysis (which mechanically filters your blood) and kidney transplant, which offers the best long-term outcomes for eligible candidates.
How CKD Affects the Rest of Your Body
Kidneys do far more than filter waste. As function declines, a cascade of complications can develop that affects your bones, heart, and blood vessels. Healthy kidneys convert vitamin D into its active form, which your body needs to absorb calcium. Damaged kidneys lose that ability, causing calcium levels to drop. In response, your parathyroid glands release extra hormone to pull calcium out of your bones and into your blood, gradually weakening your skeleton.
At the same time, failing kidneys can’t clear excess phosphorus efficiently. High phosphorus levels further drive calcium out of bones and promote calcification, a hardening of blood vessel walls that raises cardiovascular risk. This combination of bone weakening and blood vessel damage is known as mineral and bone disorder, and it can develop well before stage 5. It’s one of the reasons CKD significantly increases the risk of heart disease, even in people who never reach kidney failure.
Why Protein in Your Urine Matters
Staging by eGFR alone doesn’t tell the whole story. The amount of protein (specifically albumin) leaking into your urine is an equally important measure of kidney health. Healthy kidneys keep protein in your blood, so finding significant amounts in urine signals that the kidney’s filtering units are damaged.
Albuminuria is grouped into three categories. An albumin-to-creatinine ratio below 30 is considered normal. A ratio between 30 and 300 signals moderately increased protein loss. A ratio above 300 indicates severely increased loss. Two people can have the same eGFR but very different risk profiles depending on how much protein is escaping into their urine. Higher albuminuria at any stage means faster progression and greater risk of cardiovascular events.
Slowing Progression at Any Stage
CKD doesn’t always march steadily from stage 1 to stage 5. Many people remain stable for years or even decades, particularly if the underlying cause is well controlled. Blood pressure management is the single most important lever. Keeping blood sugar tightly controlled matters enormously for people with diabetes, since diabetes and high blood pressure together account for the majority of CKD cases worldwide.
Dietary adjustments become increasingly relevant as kidney function drops. Your kidneys become less able to handle excess potassium, phosphorus, and protein waste as they decline, but the specific limits vary widely from person to person based on lab results, body size, and the cause of kidney disease. There’s no single set of numbers that applies to everyone, which is why individualized guidance from a dietitian who specializes in kidney disease is far more useful than generic food lists.
Staying physically active, avoiding tobacco, limiting over-the-counter pain relievers that stress the kidneys (like ibuprofen and naproxen), and keeping up with regular blood work to catch changes early all contribute to slowing progression. For many people, CKD is a condition they manage for life rather than one that inevitably ends in dialysis.