Chronic kidney disease (CKD) is a gradual, lasting decline in kidney function that persists for three months or more. About 14% of adults worldwide have some form of CKD, and many don’t know it because the early stages rarely produce noticeable symptoms. The condition is defined by how well your kidneys filter waste from your blood, measured by a value called estimated glomerular filtration rate, or eGFR. An eGFR below 60 (out of a normal range around 90 to 120) lasting at least three months qualifies as CKD, as does any sign of kidney damage such as protein leaking into the urine.
What Your Kidneys Actually Do
Your kidneys filter roughly 200 liters of blood each day, removing waste products and excess fluid that leave your body as urine. They also regulate blood pressure, signal your bone marrow to produce red blood cells, and keep minerals like calcium and phosphorus in balance. When kidney function declines, all of these jobs suffer. Waste builds up in the bloodstream, fluid accumulates in tissues, and the chemical balance your body depends on starts to shift.
Unlike a sudden kidney injury from dehydration or a medication reaction, CKD involves sustained damage that scars the kidney’s internal structures over time. The tiny filtering units, the blood vessels feeding them, and the tubes that carry filtered fluid all develop scar tissue that replaces healthy tissue. Once that scarring happens, it doesn’t reverse.
The Leading Causes
Diabetes and high blood pressure together account for roughly three out of four CKD cases worldwide. Diabetes contributes about 51% and hypertension about 23%. Both conditions damage the small blood vessels inside the kidneys, and years of poorly controlled blood sugar or elevated blood pressure gradually erode filtering capacity.
Other causes include inherited conditions like polycystic kidney disease, autoimmune disorders that attack the kidney’s filters, recurring kidney infections, and prolonged use of certain over-the-counter pain relievers. Sometimes kidney disease develops without an identifiable cause, particularly in older adults whose kidney function naturally declines with age.
The Five Stages of CKD
CKD is classified into five stages based on eGFR, which estimates the volume of blood your kidneys can filter per minute. The higher the number, the better your kidneys are working.
- Stage 1 (eGFR 90 or above): Kidney function is normal or near-normal, but there’s evidence of damage, usually protein in the urine.
- Stage 2 (eGFR 60 to 89): A mild reduction in function, still typically without symptoms.
- Stage 3 (eGFR 30 to 59): Moderate loss of function. Waste products begin accumulating, and complications like anemia or bone problems may start. This stage is often split into 3a (45 to 59) and 3b (30 to 44).
- Stage 4 (eGFR 15 to 29): Severe loss of function. Symptoms become more likely, and planning for dialysis or transplant typically begins.
- Stage 5 (eGFR below 15): Kidney failure. The kidneys can no longer sustain life without dialysis or a transplant.
Why Early CKD Has No Symptoms
Your kidneys have enormous built-in reserve. You can lose more than half your filtering capacity before waste products build up enough to make you feel unwell. That’s why stages 1 through 3 are often discovered incidentally through blood or urine tests done for another reason. You can have CKD for years and feel perfectly fine.
As the disease advances into stages 4 and 5, symptoms gradually emerge: fatigue and weakness, swelling in the feet and ankles, nausea, loss of appetite, muscle cramps, itchy skin, and changes in urination. Fluid can build up in the lungs, causing shortness of breath. In the most advanced stages, some people experience difficulty concentrating or personality changes from toxin buildup affecting the brain. A sudden, unexplained increase in body weight can signal fluid retention even before visible swelling appears.
How CKD Is Diagnosed
Two simple tests form the basis of CKD screening. The first is a blood test that calculates your eGFR from a waste product called creatinine, adjusted for your age and sex. The second is a urine test called the albumin-to-creatinine ratio (uACR), which checks for protein leaking through damaged kidney filters. A uACR of 30 mg/g or higher signals kidney damage. Clinical guidelines recommend that people with diabetes get both tests at least once a year, since kidney damage can begin before any drop in eGFR shows up.
A diagnosis of CKD requires that abnormal results persist for at least three months. A single low eGFR reading could reflect temporary dehydration or illness rather than chronic disease, so retesting confirms whether the problem is ongoing.
Complications Beyond the Kidneys
CKD doesn’t just affect your kidneys. As filtering declines, the consequences ripple through multiple systems. Anemia is one of the most common complications because damaged kidneys produce less of a hormone that signals your bone marrow to make red blood cells. This can leave you feeling exhausted and short of breath even with moderate exertion.
Mineral and bone disorders are another major concern. Healthy kidneys help regulate calcium and phosphorus, but as function drops, phosphorus accumulates and calcium levels fall. Your body compensates by pulling calcium from your bones, weakening them over time. High phosphorus also contributes to calcification of blood vessels, which raises the risk of heart attack and stroke. Cardiovascular disease is actually the leading cause of death in people with CKD, more common than progression to kidney failure itself.
High blood pressure both causes and results from CKD, creating a damaging cycle. Fluid retention from poor kidney function raises blood pressure, which in turn accelerates further kidney damage.
Treatment and Slowing Progression
CKD cannot be cured, but its progression can often be slowed significantly. For decades, the standard approach centered on controlling blood pressure, managing blood sugar in people with diabetes, and using medications that reduce pressure inside the kidney’s filters to protect them from further damage.
In recent years, a newer class of medications originally developed for diabetes has changed the treatment landscape. These drugs, called SGLT2 inhibitors, have shown strong kidney-protective effects in people with CKD regardless of whether they have diabetes. They work by changing how the kidneys handle glucose and sodium, which reduces the workload on damaged filtering units. International guidelines now recommend them as a first-line treatment alongside older blood-pressure-lowering medications for many people with CKD.
For those who reach stage 5, the options are dialysis or kidney transplantation. Dialysis takes over the kidneys’ filtering job, either through a machine that cleans the blood (hemodialysis, typically three times per week) or through fluid exchanges in the abdominal cavity that can be done at home (peritoneal dialysis). A successful kidney transplant restores near-normal function, but transplanted kidneys require lifelong medications to prevent rejection.
Diet Changes That Matter
What you eat plays a real role in managing CKD. Three nutrients require the most attention: sodium, potassium, and phosphorus. Healthy adults are advised to keep sodium below 2,300 milligrams per day, but many people with CKD need to go lower. Reducing sodium helps control blood pressure and limits fluid retention. The practical steps are familiar: eat fewer processed and packaged foods, choose fresh meats over deli meats, and cook more meals from scratch so you control what goes in.
Potassium becomes a concern when kidneys can no longer excrete enough of it. High potassium levels can cause dangerous heart rhythm problems. If your levels are elevated, you may need to limit high-potassium foods like bananas, oranges, potatoes, and tomatoes. Boiling vegetables and draining the liquid can reduce their potassium content. Salt substitutes often contain potassium chloride, so check labels carefully.
Phosphorus management is trickier because the mineral hides in unexpected places. It occurs naturally in protein-rich foods like meat, dairy, and beans, but the bigger culprit is phosphorus additives in processed foods, flavored drinks, and deli meats. On ingredient labels, look for words containing “PHOS,” such as phosphoric acid or disodium phosphate. Fruits and vegetables are naturally low in phosphorus, making them good choices to fill your plate.
Protein itself may need to be moderated in earlier stages to reduce the workload on remaining kidney tissue, though the specifics vary by stage and individual. In later stages, particularly on dialysis, protein needs actually increase because dialysis removes amino acids along with waste.