Kidney disease is progressive damage to the kidneys that reduces their ability to filter waste from your blood, balance fluids, and regulate essential minerals. It affects roughly 14% of adults worldwide, and because early stages rarely produce noticeable symptoms, many people don’t know they have it until significant damage has already occurred.
What Your Kidneys Actually Do
Your kidneys are two fist-sized organs near the middle of your back, just below the rib cage. Every day they filter about 50 gallons of blood, pulling out waste products and excess water that leave your body as urine. But filtering is only part of the job. Your kidneys also regulate blood pressure, balance salt and minerals like potassium and calcium, produce a hormone that tells your bone marrow to make red blood cells, and activate vitamin D so your body can use it to keep bones strong.
When the kidneys lose function, all of these processes suffer. Waste builds up in the blood, fluid balance shifts, blood pressure climbs, bones weaken, and the body can’t produce enough red blood cells. That’s why kidney disease doesn’t just affect the kidneys. It ripples across the entire body.
Acute Versus Chronic Kidney Disease
Kidney disease comes in two broad forms. Acute kidney injury develops over hours or days, often triggered by severe dehydration, a drug reaction, an infection, or a sudden drop in blood flow to the kidneys. It can be life-threatening, but it’s frequently reversible with prompt treatment.
Chronic kidney disease (CKD) is a different situation. It’s defined as kidney damage that persists for three months or longer, with a measurable decline in how well the kidneys filter blood. CKD is not reversible. The goal of treatment is to slow progression and manage complications. Most of what people mean when they say “kidney disease” is CKD, and it’s the form that accounts for the vast majority of cases globally.
Leading Causes
Diabetes is the single biggest driver of kidney disease, responsible for nearly 40% of all kidney failure cases in the United States. High blood sugar damages the tiny blood vessels inside the kidneys over time, gradually eroding their filtering capacity. High blood pressure is the second leading cause, and it works in a similar way: sustained pressure wears down those same delicate vessels.
Other causes include autoimmune conditions like lupus, inherited disorders such as polycystic kidney disease, recurring kidney infections, prolonged obstruction from kidney stones or an enlarged prostate, and long-term use of certain pain medications. Sometimes multiple factors overlap. Someone with diabetes and high blood pressure, for example, faces a compounding risk.
Why Early Stages Feel Normal
One of the most challenging things about kidney disease is that you can lose a significant portion of kidney function before feeling anything wrong. In stages 1 and 2, the kidneys are damaged but still filtering well enough that the body compensates. Most people have no symptoms at all during this window.
As the disease progresses into stage 3 and beyond, symptoms begin to surface: fatigue, swelling in the ankles or feet, foamy or dark urine, more frequent urination (especially at night), persistent itching, nausea, and trouble concentrating. These symptoms are easy to attribute to other things, which is another reason kidney disease often goes undetected. By the time symptoms become hard to ignore, the kidneys may have lost more than half their function.
How Kidney Disease Is Staged
Doctors classify CKD into five stages based on a measurement called eGFR, which estimates how many milliliters of blood your kidneys can filter per minute. A normal eGFR is 90 or above. The stages break down like this:
- Stage 1 (eGFR 90+): Kidney damage is present (detected through urine tests or imaging) but filtering is still normal.
- Stage 2 (eGFR 60–89): A mild decrease in function, usually still without symptoms.
- Stage 3a (eGFR 45–59) and 3b (eGFR 30–44): Moderate loss of function. Complications like anemia and bone problems may begin.
- Stage 4 (eGFR 15–29): Severe loss of function. This is typically when planning for dialysis or transplant begins.
- Stage 5 (eGFR below 15): Kidney failure. The kidneys can no longer sustain life without dialysis or a transplant.
An important detail: a low-normal eGFR alone doesn’t mean you have CKD. Stages 1 and 2 only count as kidney disease if there’s also evidence of actual damage, such as protein leaking into the urine or structural abnormalities visible on imaging.
How It’s Detected
Two simple tests catch kidney disease early. The first is a blood test that estimates your eGFR from a waste product called creatinine. The second is a urine test that checks for albumin, a protein that healthy kidneys keep in the blood. When albumin shows up in the urine at levels above 30 mg/g, it signals that the kidney’s filters are leaking, a hallmark of early damage.
Higher levels of albumin in the urine (above 300 mg/g) indicate more advanced damage. Because these tests are inexpensive and widely available, screening is straightforward for anyone with diabetes, high blood pressure, or a family history of kidney problems.
What Happens to the Rest of the Body
As kidney function declines, the consequences extend well beyond fluid and waste buildup.
Anemia is one of the most common complications. Damaged kidneys produce less of the hormone that signals bone marrow to make red blood cells. With fewer red blood cells carrying oxygen to your tissues, you feel exhausted, weak, and short of breath. This can start as early as stage 3 and worsens as the disease progresses.
Bone disease is another major concern. The kidneys activate vitamin D, which your body needs to absorb calcium. When that process breaks down, calcium gets pulled from the bones, leaving them brittle and prone to fractures. At the same time, phosphorus builds up in the blood because the kidneys can no longer clear it efficiently, which accelerates bone loss and can cause calcium deposits in blood vessels and soft tissues.
Heart disease is tightly linked to kidney disease as well. Fluid overload strains the heart, and the mineral imbalances that come with declining kidney function increase the risk of dangerous heart rhythms. In fact, cardiovascular disease is the leading cause of death in people with CKD, not kidney failure itself.
Managing Kidney Disease
There is no cure for CKD, but the rate of progression varies enormously depending on how it’s managed. For most people, the strategy centers on controlling the conditions that caused the damage in the first place. Keeping blood sugar in a healthy range if you have diabetes and maintaining normal blood pressure are the two most impactful things you can do. Certain blood pressure medications also have a direct protective effect on the kidneys, independent of their blood pressure benefits.
Diet plays a significant role, though the specifics depend on your stage and lab results. In general, reducing sodium helps control blood pressure and fluid retention. As kidney function drops further, you may need to limit potassium and phosphorus because the kidneys can no longer regulate these minerals effectively. The right amounts are highly individual, so dietary changes work best when guided by a dietitian who specializes in kidney disease.
Staying physically active, not smoking, and avoiding medications that stress the kidneys (including common over-the-counter anti-inflammatory drugs like ibuprofen) all help preserve remaining function.
When the Kidneys Can No Longer Keep Up
Once eGFR drops below 15, the kidneys are in failure and can no longer sustain life on their own. At this point, the two options are dialysis or a kidney transplant. Current guidelines recommend monitoring closely at this stage and beginning dialysis when symptoms demand it or when eGFR falls to 6 or below, rather than starting early based on numbers alone.
Dialysis takes over the kidneys’ filtering job, either through a machine that cleans the blood externally (hemodialysis, typically three sessions per week at a clinic) or through a fluid exchange in the abdomen that you can do at home (peritoneal dialysis). Both are effective at removing waste and excess fluid, but neither replaces the kidneys’ hormonal functions, so additional treatments for anemia and bone health remain necessary.
A kidney transplant offers the closest thing to normal kidney function. A transplanted kidney takes over filtering, hormone production, and mineral regulation. Not everyone is a candidate, and the wait for a donor organ can be years long, but transplant recipients generally have better long-term outcomes and quality of life than those on dialysis.