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What Is Nephrology?

Nephrology is the branch of internal medicine that deals with the kidneys — their normal function, their diseases, and what happens when they fail. The word comes from the Greek nephros (kidney) and logos (study), and if you’ve ever had a blood test that checked your “kidney function,” you’ve already brushed up against the edges of this specialty.

Your kidneys don’t get much attention until something goes wrong with them. They sit quietly behind your abdominal organs, about the size of your fists, doing work that would kill you within days if it stopped. Roughly 37 million Americans have chronic kidney disease, and most of them don’t know it. That gap between how important kidneys are and how little people think about them is basically the story of nephrology.

What Your Kidneys Actually Do

Most people know that kidneys “filter blood.” That’s true but wildly understated. Here’s what’s actually happening:

Filtration: Your kidneys filter about 150 quarts (roughly 140 liters) of blood every day. They process your entire blood volume approximately 30 times per day. The filtration units — called nephrons — number about one million per kidney. Each nephron is a tiny, exquisitely designed structure that filters blood through a capillary tuft called the glomerulus, then reabsorbs what the body needs and excretes what it doesn’t.

Waste removal: The kidneys remove metabolic waste products — urea (from protein breakdown), creatinine (from muscle metabolism), uric acid, and various drug metabolites. Without this, toxins would accumulate in your blood within hours.

Fluid balance: Your kidneys regulate how much water your body retains or excretes. Drink a liter of water? Your kidneys will increase urine production to keep your blood volume stable. Dehydrated? They’ll concentrate your urine to conserve water. This adjustment happens continuously, in real time.

Electrolyte regulation: Sodium, potassium, calcium, phosphorus, magnesium — your kidneys keep all of these within narrow ranges. This matters more than it sounds. If your potassium level goes too high, your heart can stop. If your calcium drops too low, your muscles seize up. Your kidneys are the reason these numbers stay where they should be.

Blood pressure control: The kidneys regulate blood pressure through multiple mechanisms — controlling sodium and water balance, producing an enzyme called renin that activates the renin-angiotensin-aldosterone system (RAAS), and responding to hormonal signals. Many blood pressure medications work by targeting kidney-related pathways.

Hormone production: Kidneys produce erythropoietin (EPO), which tells your bone marrow to make red blood cells. They also activate vitamin D, which is essential for calcium absorption and bone health. Kidney failure causes anemia and bone disease partly because these hormonal functions are lost.

Acid-base balance: Your kidneys help maintain blood pH in the narrow range (7.35-7.45) necessary for survival. They excrete hydrogen ions and reabsorb bicarbonate to keep your blood from becoming too acidic or too alkaline.

That’s a lot of jobs for two organs that weigh about 5 ounces each.

Chronic Kidney Disease

Chronic kidney disease (CKD) is the gradual, usually irreversible loss of kidney function over months or years. It’s staged from 1 (mild, kidney damage with normal function) to 5 (kidney failure, also called end-stage renal disease or ESRD).

How Common Is It?

Very. An estimated 37 million Americans — about 15% of the adult population — have CKD. Globally, the figure is roughly 850 million people. It’s the 12th leading cause of death worldwide, and its prevalence is increasing, driven primarily by diabetes and hypertension.

The Two Main Causes

Diabetes causes about 44% of new kidney failure cases in the United States. High blood sugar damages the tiny blood vessels in the glomeruli over time, gradually destroying the kidney’s filtration capacity. This is called diabetic nephropathy, and it’s the single biggest reason people end up on dialysis.

High blood pressure causes about 29% of kidney failure cases. Elevated pressure damages blood vessels throughout the body, including those in the kidneys. The irony is that damaged kidneys also raise blood pressure, creating a destructive feedback loop.

Together, diabetes and hypertension account for nearly three-quarters of all kidney failure. Controlling these two conditions is, by a wide margin, the most effective way to prevent CKD.

Other Causes

Glomerulonephritis — inflammation of the kidney’s filtering units, caused by immune disorders, infections, or genetic conditions
Polycystic kidney disease (PKD) — a genetic condition where fluid-filled cysts grow in the kidneys, gradually destroying functional tissue. About 600,000 Americans have PKD
Lupus nephritis — kidney damage from systemic lupus erythematosus
Obstructive uropathy — blockages that prevent urine from draining, causing back-pressure damage
Drug toxicity — chronic use of NSAIDs (ibuprofen, naproxen), certain antibiotics, and other medications can damage kidneys over time

Dialysis — When Kidneys Fail

When kidney function drops below about 10-15% of normal, the body can no longer survive without help. That help comes in two forms: dialysis or transplantation.

Hemodialysis

The patient’s blood is pumped through a machine containing a semipermeable membrane. Waste products and excess fluid pass through the membrane into a cleansing solution (dialysate) and are removed. The cleaned blood is returned to the body.

Most hemodialysis patients go to a dialysis center three times per week for sessions lasting 3-5 hours each. Some patients do home hemodialysis, which allows more flexible scheduling and, in some studies, better outcomes.

It works — it keeps people alive who would otherwise die within weeks. But it’s far from pleasant. Common side effects include fatigue, muscle cramps, low blood pressure during treatment, nausea, and difficulty sleeping. Hemodialysis replaces only about 10-15% of normal kidney function, so patients still experience many consequences of kidney failure.

Peritoneal Dialysis

Instead of an external machine, this method uses the patient’s own peritoneal membrane (the lining of the abdominal cavity) as the filter. A catheter is surgically placed in the abdomen. Dialysate is pumped in, left for several hours to absorb waste products, then drained and replaced.

Peritoneal dialysis can be done at home — many patients do it overnight while sleeping. It offers more independence than hemodialysis and avoids the hemodynamic stress of rapid fluid removal. However, it carries a risk of peritonitis (infection of the abdominal lining) and eventually the peritoneal membrane loses effectiveness over years of use.

Kidney Transplantation

A transplant is the best treatment for most patients with kidney failure. Transplant recipients live longer, have better quality of life, and face fewer dietary restrictions than dialysis patients. A functioning transplanted kidney replaces nearly all lost kidney function.

The problem is supply. As of 2024, over 89,000 people in the United States are on the waiting list for a kidney transplant. About 25,000 kidney transplants are performed each year — roughly 17,000 from deceased donors and 6,000 from living donors. The median wait time is 3-5 years, and thousands of people die each year while waiting.

Living donor transplantation offers the best outcomes and shortest wait times. A healthy person can safely donate one kidney — the remaining kidney compensates, and donors have normal life expectancies. But finding a compatible living donor isn’t always possible.

What Nephrologists Actually Do

A nephrologist’s day-to-day work includes:

Managing patients with CKD across all stages
Supervising dialysis treatments and managing complications
Evaluating and preparing patients for kidney transplantation
Treating acute kidney injury (sudden kidney failure from infection, medication reactions, or severe dehydration)
Managing electrolyte disorders — dangerously high potassium, low sodium, abnormal calcium
Treating glomerular diseases and autoimmune kidney conditions
Performing kidney biopsies (inserting a needle through the skin to obtain a small sample of kidney tissue for diagnosis)
Managing hypertension that doesn’t respond to standard treatment

Becoming a nephrologist requires completing medical school (4 years), internal medicine residency (3 years), and a nephrology fellowship (2-3 years) — a minimum of 9-10 years of post-college training.

Prevention — The Best Nephrology

Here’s the frustrating truth about kidney disease: by the time most people are diagnosed, significant damage has already occurred. Kidneys are resilient — they can lose over 50% of their function before symptoms appear. That resilience is both a strength and a curse, because it means early kidney disease is invisible without blood and urine testing.

The most effective prevention strategies are straightforward:

Control blood sugar if you have diabetes. Maintaining an A1C below 7% significantly reduces kidney damage risk.
Control blood pressure. The current target for most adults is below 130/80 mmHg. For people with CKD, even lower may be beneficial.
Don’t overuse NSAIDs. Ibuprofen and naproxen are hard on kidneys, especially with chronic use.
Stay hydrated. Adequate water intake helps kidneys function efficiently.
Get screened. If you have diabetes, hypertension, or a family history of kidney disease, regular blood tests (creatinine, eGFR) and urine tests (albumin-to-creatinine ratio) can catch problems early.

The field of nephrology is essentially a race between prevention and damage — trying to catch kidney disease before it becomes irreversible, and managing it as effectively as possible when it does. That race is worth running, because the alternative — dialysis or transplantation — is something everyone involved would rather avoid.

Frequently Asked Questions

What is the difference between a nephrologist and a urologist?

Nephrologists are internal medicine doctors who specialize in the medical management of kidney disease — they treat conditions with medications, dialysis, and lifestyle changes. Urologists are surgeons who handle structural and anatomical problems of the urinary tract and male reproductive system, including kidney stones that need surgical removal, bladder issues, and prostate conditions. If you have chronic kidney disease, you see a nephrologist. If you need surgery on your urinary tract, you see a urologist.

Can you live with only one kidney?

Yes. One healthy kidney can filter blood effectively enough to maintain normal health. Many people are born with a single functioning kidney and never know it. Kidney donors live normal lifespans with one kidney, though they should have regular checkups and avoid activities that risk kidney injury. The remaining kidney typically enlarges slightly to compensate for the missing one.

What are the early signs of kidney disease?

Early kidney disease often has no symptoms — which is why it's sometimes called a 'silent' disease. As it progresses, signs may include fatigue, swollen ankles or feet, frequent urination (especially at night), foamy or bloody urine, persistent itching, nausea, and difficulty concentrating. By the time symptoms appear, significant kidney damage may already have occurred, which is why regular screening is important for people with diabetes or high blood pressure.

How long can you live on dialysis?

Average life expectancy on dialysis varies widely depending on age, overall health, and other conditions. The five-year survival rate for patients on dialysis is approximately 35-40%, though some patients live 20+ years on treatment. Younger, healthier patients generally do better. A kidney transplant, when available, typically offers better long-term survival and quality of life than long-term dialysis.