When your kidneys fail, waste products and excess fluid build up in your blood because your body loses its primary filtration system. This triggers a cascade of problems that affects nearly every organ, from your heart and bones to your brain and skin. Kidney failure can happen suddenly over days (acute kidney injury) or gradually over months to years (chronic kidney disease), and the consequences vary depending on how much function remains and how quickly it’s lost.
How Kidney Function Is Measured
Doctors track kidney health using a number called the estimated glomerular filtration rate, or eGFR, which measures how efficiently your kidneys filter blood. A normal eGFR is 90 or above. Chronic kidney disease is classified in five stages based on this number:
- Stage 1 (eGFR 90+): Kidney damage is present but filtration is still normal
- Stage 2 (eGFR 60–89): Mild loss of function
- Stage 3a (eGFR 45–59): Mild to moderate loss
- Stage 3b (eGFR 30–44): Moderate to severe loss
- Stage 4 (eGFR 15–29): Severe loss of function
- Stage 5 (eGFR below 15): Kidney failure
Many people in stages 1 and 2 have no symptoms at all. The effects described below become more pronounced as eGFR drops, with the most serious consequences concentrated in stages 4 and 5.
Waste Buildup in the Blood
The most immediate consequence of kidney failure is a condition called uremia, where nitrogen-containing waste products that are normally filtered out accumulate in your bloodstream. This toxic buildup disrupts cell function throughout the body, impairing how proteins are transported, how genetic instructions are processed, and how cells respond to stress.
Uremia affects the nervous system, potentially causing confusion, difficulty concentrating, and nerve damage in the hands and feet. It disrupts digestive function too, causing nausea, loss of appetite, and a persistent metallic taste in your mouth. In severe, untreated cases, your breath can develop an ammonia-like smell. At the most extreme end, dried sweat can leave yellow-white crystals on your skin, a phenomenon called uremic frost. These late-stage symptoms are rare today because most people begin treatment before reaching that point.
Heart Rhythm and Potassium Danger
Your kidneys are responsible for keeping potassium levels in a tight range, and when they fail, potassium accumulates in the blood. This is one of the most immediately dangerous effects of kidney failure. Elevated potassium disrupts the electrical signals that coordinate your heartbeat, and research published in the Journal of the American Heart Association found that patients with high potassium had a 59% greater risk of being hospitalized for an abnormal heart rhythm compared to those with normal levels. The most common rhythm disturbance was atrial fibrillation, accounting for about 63% of these events.
Potassium isn’t the only electrolyte thrown off balance. Sodium and acid levels also become harder for the body to regulate, leading to fluid retention, swelling in the legs and ankles, and shortness of breath as fluid can back up into the lungs.
Anemia and Constant Fatigue
Healthy kidneys produce a hormone called erythropoietin (EPO), which signals your bone marrow to make red blood cells. The cells that produce EPO live in the kidney’s outer layers, and their numbers are normally low but ramp up whenever your body senses it needs more oxygen-carrying capacity. In kidney failure, something different happens: the EPO-producing cells transform into scar-tissue cells called myofibroblasts. These transformed cells stop making EPO and instead contribute to further kidney scarring, creating a vicious cycle.
The result is a steady drop in red blood cell production. With fewer red blood cells circulating, less oxygen reaches your muscles, brain, and other tissues. This is why people with advanced kidney disease often feel profoundly tired, short of breath during light activity, and mentally foggy. The anemia tends to worsen as kidney function declines further.
Bone Weakening and Mineral Imbalance
Kidneys play a critical role in keeping your bones strong by balancing calcium, phosphorus, and vitamin D. When they fail, phosphorus that would normally be excreted starts accumulating in the blood. The body tries to compensate in two ways, both of which backfire over time.
First, bone cells release a hormone called FGF-23 to force the kidneys to dump more phosphorus. But FGF-23 also suppresses vitamin D activation, which means your gut absorbs less calcium from food. Second, your parathyroid glands ramp up production of parathyroid hormone (PTH) to pull calcium from your bones directly, trying to keep blood calcium levels stable. This accelerated bone breakdown releases even more phosphorus into circulation, worsening the imbalance.
The long-term damage to bone takes several forms. High PTH levels can cause excessive bone turnover, where bone is broken down and rebuilt so rapidly that the new bone is weak and fibrous. Alternatively, if PTH becomes over-suppressed by treatment, bone turnover slows too much, leaving bones brittle from inactivity. Low vitamin D levels can also prevent minerals from being deposited properly, softening the bone structure. All of these patterns increase fracture risk significantly.
Acute vs. Chronic Kidney Failure
These consequences play out differently depending on whether kidney failure develops suddenly or gradually. Acute kidney injury can strike over hours to days and falls into three categories based on where the problem originates. Prerenal causes involve reduced blood flow to the kidneys, often from severe dehydration, major blood loss, heart failure, or sepsis. Intrinsic causes involve direct damage to the kidney tissue itself, from infections, toxins, or inflammation. Postrenal causes involve a blockage preventing urine from draining, such as kidney stones, an enlarged prostate, or tumors pressing on the urinary tract.
Acute kidney injury is often reversible if the underlying cause is treated quickly. Chronic kidney disease, on the other hand, involves gradual, usually permanent loss of function over months or years. Diabetes and high blood pressure are the two leading causes. Because the decline is slow, the body partially adapts to rising waste levels, which is why many people with chronic kidney disease feel relatively normal until they’ve lost 70% or more of their kidney function.
What Dialysis Involves
When kidneys can no longer sustain life on their own, dialysis takes over the job of filtering blood. There are two main types, and they work quite differently in practice.
Hemodialysis routes your blood through an external machine that removes waste and excess fluid, then returns the cleaned blood to your body. It requires a surgically created access point, usually in the arm, where an artery and vein are connected. Most people on hemodialysis visit a clinic three to five times per week for sessions that typically last several hours.
Peritoneal dialysis uses the lining of your abdomen as a natural filter. A surgeon places a permanent tube into the abdominal cavity, and you fill it with a special cleansing fluid that draws waste through the abdominal walls. The fluid is then drained and replaced. This can be done continuously during the day or overnight using an automated cycler. Because it’s done at home, peritoneal dialysis allows some people to continue working and maintain a more flexible schedule.
Dietary Changes in Kidney Failure
As kidney function declines, what you eat and drink starts to matter more because your body can no longer easily clear certain substances. Sodium is one of the first nutrients to be restricted. The general dietary guideline for adults is no more than 2,300 milligrams per day, but many people with kidney failure need to stay well below that to control blood pressure and fluid retention.
Potassium restrictions become important to protect heart rhythm. This means limiting foods like bananas, oranges, potatoes, and tomatoes. Phosphorus intake is managed to slow bone damage, which often means cutting back on dairy, processed foods, and dark sodas. Protein is a balancing act: your body needs it for repair and nutrition, but protein metabolism generates the very waste products your kidneys can no longer clear efficiently. A dietitian typically works with each person to find the right balance based on their stage of disease and whether they’re on dialysis.
Fluid intake may also be limited, especially for people who notice swelling or whose urine output has dropped significantly. The specifics vary from person to person, and the restrictions generally tighten as kidney function worsens.
Survival and Long-Term Outlook
Kidney failure is a serious condition, but it is not an immediate death sentence. According to 2025 data from the United States Renal Data System, the five-year survival rate for people who started hemodialysis in 2019 was about 41%, while those who started peritoneal dialysis had a slightly higher five-year survival of 43%. These numbers reflect all age groups combined, and younger patients generally fare better than older ones, though survival in the 18-to-44 age group has slightly worsened in recent years for reasons still being studied.
Kidney transplantation offers significantly better long-term outcomes than dialysis for those who qualify, with most transplant recipients living well beyond the five-year mark. The wait for a donor kidney can be long, and not everyone is a candidate, but it remains the closest thing to restoring normal kidney function.