Nephrology is the branch of medicine focused on kidney health. It covers everything from diagnosing early kidney damage to managing kidney failure with dialysis or transplantation. Nephrologists are internal medicine doctors with additional specialty training, and they treat conditions that extend well beyond the kidneys themselves, including high blood pressure, fluid imbalances, and disruptions in essential minerals like sodium, potassium, and calcium.
What the Kidneys Actually Do
Your kidneys filter about 50 gallons of blood every day, removing metabolic waste and excess fluid that leave the body as urine. But filtration is only part of their job. They also regulate blood pressure by releasing a hormone called renin, which triggers a chain reaction that tightens blood vessels and tells the body to hold onto sodium and water. When blood pressure drops or the kidneys sense reduced blood flow, this system ramps up automatically.
Kidneys also help maintain bone strength by activating vitamin D, stimulate red blood cell production through a signaling hormone, and keep electrolytes like potassium, sodium, and calcium within tight ranges. Because these functions touch so many other systems, kidney problems often show up as high blood pressure, anemia, bone weakness, or dangerous shifts in blood chemistry rather than obvious kidney pain.
Conditions Nephrologists Treat
The specialty covers a wide range of problems. The most common include chronic kidney disease (CKD), kidney stones, protein in the urine (a sign of kidney damage), high blood pressure tied to kidney dysfunction, and acute kidney injury from infection, dehydration, or medication side effects. Nephrologists also manage glomerulonephritis (inflammation of the kidney’s filtering units), polycystic kidney disease, and electrolyte disorders that affect heart rhythm and muscle function.
Diabetes and high blood pressure are the two leading causes of kidney disease, so nephrologists spend a significant portion of their time working with patients who have these conditions. When kidney function declines far enough, the specialty also encompasses dialysis management and preparation for kidney transplantation.
How Kidney Function Is Measured
Two lab values form the backbone of kidney diagnosis. The first is estimated glomerular filtration rate, or eGFR, which measures how efficiently your kidneys filter blood. It’s calculated from a blood test for creatinine (a waste product from normal muscle activity), adjusted for age and sex. A higher eGFR means better kidney function. The second is the urine albumin-to-creatinine ratio (UACR), which checks for albumin, a protein that shouldn’t be leaking into urine in significant amounts. A UACR above 30 mg/g signals kidney damage.
eGFR is more reliable than creatinine alone because creatinine levels are influenced by muscle mass, body size, and diet. That said, eGFR isn’t accurate in people whose creatinine is changing rapidly or who have extreme variations in muscle mass. For people with diabetes, both tests are recommended yearly to catch kidney damage early.
The Five Stages of Chronic Kidney Disease
CKD is classified into five stages based on eGFR:
- Stage 1: eGFR 90 or above. Kidney function is normal, but there’s evidence of damage such as protein in the urine.
- Stage 2: eGFR 60 to 89. Mild loss of function.
- Stage 3a: eGFR 45 to 59. Mild to moderate loss.
- Stage 3b: eGFR 30 to 44. Moderate to severe loss.
- Stage 4: eGFR 15 to 29. Severe loss of function. This is typically when preparation for dialysis or transplant begins.
- Stage 5: eGFR below 15. Kidney failure. The kidneys can no longer sustain life without dialysis or a transplant.
Many people live in stages 1 through 3 for years without symptoms. By stage 4, fatigue, swelling, changes in urination, and nausea become more common as waste products accumulate in the blood.
Dialysis: Hemodialysis vs. Peritoneal Dialysis
When kidneys fail, dialysis takes over their filtering work. There are two main types. Hemodialysis pumps blood through an external machine that removes waste and excess fluid, then returns the cleaned blood to the body. It’s typically done at a dialysis center three times a week, with each session lasting about four hours.
Peritoneal dialysis uses the lining of your abdominal cavity as a natural filter. A cleansing fluid is infused through a permanent catheter in the abdomen, absorbs waste over several hours, and is then drained. Many people do this at home, either overnight with a machine or through manual exchanges during the day.
Research comparing the two approaches shows peritoneal dialysis is better at maintaining stable blood pressure, preserving remaining kidney function, and clearing certain waste molecules. It also carries a lower overall rate of complications. Hemodialysis, on the other hand, is more effective at maintaining albumin levels, an important protein for nutrition. The best choice depends on a person’s lifestyle, other health conditions, and home environment.
Kidney Transplantation
For many people with kidney failure, transplantation offers the best long-term outcome. Nephrologists are involved from the earliest stages, evaluating whether a patient is a good candidate, managing their health while they wait for a donor kidney, and handling the complex medical care that follows surgery. After transplantation, a transplant nephrologist manages medications that prevent the body from rejecting the new kidney, watches for signs of graft problems, and monitors for the return of the original kidney disease. This post-transplant care continues for life.
Nephrology vs. Urology
These two specialties overlap in territory but differ sharply in approach. Nephrologists are medical doctors who treat kidney disease with medications, dialysis, and ongoing management. They do not perform surgery. Urologists are surgeons who treat structural and anatomical problems of the entire urinary tract, including the kidneys, bladder, ureters, and urethra. If you have a kidney stone that needs to be physically removed, that’s urology. If your kidneys are gradually losing function because of diabetes, that’s nephrology.
In practice, a primary care doctor will refer you to one or the other based on the nature of the problem. Conditions like kidney cancer, large stones, and urinary obstruction go to urology. Chronic kidney disease, electrolyte disorders, uncontrolled hypertension related to kidney function, and kidney inflammation go to nephrology.
Training and Education
Becoming a nephrologist requires a long training path. After medical school, a physician completes at least three years of internal medicine residency, then enters a nephrology fellowship lasting 24 months. The fellowship, accredited by the ACGME, covers dialysis procedures, transplant medicine, kidney biopsy interpretation, and management of complex electrolyte and acid-base disorders. After fellowship, most nephrologists pursue board certification. The specialty has existed for roughly 60 years, growing from early research into kidney physiology and blood pressure regulation into a field that now spans acute care, chronic disease management, and transplant medicine.