Chronic kidney disease (CKD) is classified into five stages based on how well your kidneys filter waste from your blood. The key measurement is your estimated glomerular filtration rate, or eGFR, a number derived from a simple blood test. A normal eGFR is 90 or above, and stage 5 (the most severe) begins below 15. Most people have no symptoms until the later stages, which is why routine blood work catches many cases long before you feel anything wrong.
How Kidney Function Is Measured
Your eGFR estimates how many milliliters of blood your kidneys can filter per minute. It’s calculated from a blood test that measures creatinine, a waste product your muscles produce at a fairly steady rate. Healthy kidneys clear creatinine efficiently, so when levels rise in the blood, it signals that filtration is slowing down.
Creatinine-based eGFR is the standard screening tool, but it has blind spots. Because creatinine levels are influenced by muscle mass, age, and sex, the number can be misleading in people who are very muscular, very thin, or elderly. In those situations, doctors may add a second blood marker called cystatin C. Using both markers together gives a more accurate picture of true kidney function than either one alone. Cystatin C has its own limitations: it can read falsely high in people with chronic inflammation, obesity, or thyroid problems.
The Five Stages at a Glance
Each stage corresponds to an eGFR range:
- Stage 1: eGFR 90 or above. Kidney function is normal or near-normal, but there’s evidence of kidney damage (such as protein in the urine or structural abnormalities on imaging).
- Stage 2: eGFR 60 to 89. A mild decrease in filtration, again with some marker of damage present.
- Stage 3a: eGFR 45 to 59. Mild-to-moderate loss of function.
- Stage 3b: eGFR 30 to 44. Moderate-to-severe loss of function.
- Stage 4: eGFR 15 to 29. Severe loss of function.
- Stage 5: eGFR below 15. The kidneys can no longer sustain life without treatment.
An eGFR of 60 to 89 on its own, without any other sign of kidney damage, does not automatically mean you have CKD. Plenty of older adults fall into that range as a normal part of aging. A diagnosis requires either a low eGFR or evidence of damage (protein in the urine, abnormal imaging, or a history of a kidney transplant) that persists for at least three months.
Why Protein in Your Urine Matters
Staging isn’t based on eGFR alone. Doctors also check how much albumin, a type of protein, is leaking into your urine. Healthy kidneys keep albumin in the blood, so finding it in urine signals that the kidney’s filtering units are damaged. This is measured with a urine albumin-to-creatinine ratio (ACR):
- A1 (normal to mildly increased): ACR below 30 mg/g
- A2 (moderately increased): ACR 30 to 300 mg/g
- A3 (severely increased): ACR above 300 mg/g
Your overall risk depends on where you fall on both scales. Someone with an eGFR of 50 and normal urine albumin faces a very different outlook than someone with the same eGFR but heavily elevated albumin. The international guidelines from KDIGO use a color-coded “heat map” that combines these two numbers into four risk categories: low, moderately increased, high, and very high. Your risk category, not just your stage number, drives decisions about how often you need monitoring and how aggressively your condition should be managed.
Stage 3: The Critical Dividing Line
Stage 3 is where most people first learn they have kidney disease, and it covers a wide range of function. That’s why it was split into 3a and 3b. The distinction matters clinically: research published in Kidney International found that people with an eGFR below 45 (stage 3b), especially older patients, experience noticeably faster disease progression than those in stage 3a. If you’re in stage 3b, earlier referral to a kidney specialist is generally recommended.
At stage 3, screening for complications begins in earnest. Your doctor will typically check for anemia at least once a year and start monitoring calcium, phosphorus, and parathyroid hormone levels every 6 to 12 months. These screenings aren’t routine in stages 1 and 2 because the kidneys are still handling most of their regulatory duties. By stage 3, the kidneys begin struggling to manage minerals and produce enough of the hormone that stimulates red blood cell production.
What Symptoms Feel Like
Stages 1 through 3a are almost always silent. You won’t feel your kidneys declining, and blood pressure may be the only outward clue. This is what makes CKD dangerous: by the time you notice something is off, significant damage has already occurred.
Symptoms typically surface in advanced disease, around stages 4 and 5. These can include persistent nausea, loss of appetite, fatigue and weakness, trouble sleeping, difficulty concentrating or thinking clearly, and shortness of breath if fluid accumulates in the lungs. Blood pressure often becomes increasingly difficult to control. None of these symptoms are unique to kidney disease, which is another reason it goes unrecognized without lab work.
Complications That Develop as Stages Progress
As kidney function drops, several problems emerge because the kidneys do far more than filter waste. They regulate blood pressure, balance minerals, maintain bone health, and produce hormones. When filtration declines, each of these systems starts to falter.
Anemia becomes more common starting at stage 3 because the kidneys produce less of the hormone that tells your bone marrow to make red blood cells. By stage 4, screening for anemia happens at least twice a year. Bone disease is another major concern: the kidneys help activate vitamin D and regulate calcium and phosphorus. When those systems break down, bones can weaken and calcium can deposit in blood vessels. Potassium levels may rise, which can affect heart rhythm, and acid can build up in the blood as the kidneys lose their ability to maintain the body’s pH balance.
Dietary Changes by Stage
Protein management is one of the most concrete things you can control. In stages 3 through 5 (before dialysis), guidelines recommend lowering protein intake to about 0.55 to 0.60 grams per kilogram of body weight per day. For a 150-pound person, that works out to roughly 37 to 41 grams of protein daily, significantly less than what most people eat. If you also have diabetes, the target is slightly more flexible at 0.6 to 0.8 grams per kilogram per day.
Once someone begins dialysis, the equation reverses. Dialysis removes amino acids and protein during treatment, so the recommended intake jumps to 1.0 to 1.2 grams per kilogram per day, regardless of diabetes status. This shift catches many people off guard because they’ve spent months or years limiting protein, only to be told they now need to eat more of it. Working with a dietitian who specializes in kidney disease makes these transitions much easier to navigate.
Beyond protein, sodium and potassium restrictions often come into play at later stages. Fluid intake may also need to be limited if your body starts retaining water.
Stage 5 and Kidney Replacement
Stage 5 is sometimes called end-stage kidney disease. At an eGFR below 15, the kidneys can no longer keep you alive on their own. Treatment options at this point are dialysis or a kidney transplant.
The timing of dialysis initiation is individualized. It doesn’t automatically start the moment you hit stage 5. Doctors weigh your symptoms, lab trends, nutritional status, and quality of life. Planning for dialysis or transplant evaluation typically begins well before it’s needed, often during stage 4, so there’s time to create vascular access for dialysis or get on a transplant waiting list. Starting that planning early reduces the chance of an emergency dialysis start, which carries higher risks and worse outcomes.
A kidney transplant, when available, generally offers better long-term survival and quality of life compared to remaining on dialysis. Living-donor transplants can sometimes be performed before dialysis is ever needed, a process called preemptive transplantation.
Slowing Progression at Any Stage
CKD doesn’t always march steadily from one stage to the next. With the right management, many people stabilize or slow the decline significantly. Blood pressure control is the single most impactful factor. Certain blood pressure medications also reduce protein leakage into the urine, which independently slows kidney damage. Blood sugar control in diabetes is equally critical, since diabetes is the leading cause of CKD worldwide.
Other modifiable factors include maintaining a healthy weight, stopping smoking, staying physically active, and avoiding medications that stress the kidneys, particularly over-the-counter anti-inflammatory painkillers like ibuprofen and naproxen. Newer medications originally developed for diabetes have also shown significant kidney-protective effects in people with CKD, even those without diabetes. These drugs work partly by reducing pressure inside the kidney’s filtering units.