A nephrologist is a doctor who specializes in diagnosing and treating kidney diseases. They manage everything from chronic kidney disease and hard-to-control blood pressure to dialysis and kidney transplant care. Most people see a nephrologist after a referral from their primary care doctor, typically because blood work or urine tests flagged a problem with kidney function.
Conditions Nephrologists Treat
The kidney’s job extends well beyond making urine. Your kidneys filter waste, balance fluid levels, regulate blood pressure, and keep electrolytes like sodium and potassium in check. When any of those functions break down, a nephrologist steps in. The most common conditions they manage include chronic kidney disease, kidney failure, high blood pressure linked to kidney problems, diabetes-related kidney damage, kidney stones, kidney infections, cystic kidney disease, and electrolyte disorders like low sodium (hyponatremia) or high potassium.
They also treat less common but serious conditions like glomerulonephritis (inflammation of the kidney’s filtering units), nephrotic syndrome (when damaged kidneys leak large amounts of protein into urine), and hemolytic uremic syndrome. In some cases, nephrologists manage toxic overdoses that require dialysis to clear harmful substances from the blood.
How Kidney Function Is Tested
The single most important number in nephrology is your glomerular filtration rate, or GFR. This estimates how efficiently your kidneys filter blood each minute. A healthy GFR is 90 or above. Nephrologists calculate it using a simple blood test that measures creatinine, a waste product your muscles produce at a steady rate. When kidneys slow down, creatinine builds up, and the GFR drops.
The other key test measures how much protein, specifically albumin, is leaking into your urine. Healthy kidneys keep protein in the blood. When albumin shows up in urine, it signals damage to the kidney’s filtering system. This can be checked with a single urine sample or a 24-hour urine collection.
Beyond those two core tests, nephrologists use a range of tools depending on the situation. A standard urine dipstick can detect blood, glucose, and signs of infection. Microscopic analysis of urine can reveal abnormal cells, crystals, or casts that point to specific diseases. For harder-to-pin-down diagnoses, a kidney biopsy (removing a tiny tissue sample with a needle) gives a direct look at what’s happening inside the organ. Blood tests measuring sodium, potassium, calcium, and phosphorus levels help the nephrologist understand how well the kidneys are maintaining the body’s chemical balance.
Managing High Blood Pressure
Kidneys and blood pressure are deeply connected. When kidney function declines, the body retains extra fluid, which raises blood pressure. At the same time, the kidneys ramp up hormonal signals that tighten blood vessels. This creates a cycle: high blood pressure damages kidneys further, and worsening kidneys push blood pressure higher.
Nephrologists specialize in blood pressure that doesn’t respond to standard treatment. If your blood pressure stays above 150/90 despite three or four medications, that’s considered resistant hypertension, and it often points to an underlying kidney or hormonal cause. Nephrologists also look for secondary causes like excess aldosterone (a hormone that makes the body hold onto salt) or narrowing of the arteries that supply the kidneys. Controlling fluid balance through diet, medication, or dialysis is central to how nephrologists bring blood pressure under control in advanced kidney disease.
Chronic Kidney Disease Stages
Chronic kidney disease is classified into five stages based on GFR. Stage 1 means the GFR is 90 or higher but there’s already some sign of kidney damage, like protein or blood in the urine. Stage 2 is a GFR of 60 to 89 with similar markers. Many people in stages 1 and 2 have no symptoms and are managed by their primary care doctor.
Stages 3 through 5 represent progressively lower kidney function, and this is where nephrologists take a larger role. International guidelines generally recommend referral to a nephrologist when GFR drops below 30 (stage 4), or earlier if the GFR is declining rapidly, more than 5 points per year. Significant protein in the urine, unexplained blood in the urine, or blood pressure that resists multiple medications are also triggers for referral. Stage 5, with a GFR below 15, is kidney failure. At that point, dialysis or a transplant becomes necessary to survive.
Dialysis Oversight
When kidneys can no longer clean the blood adequately, dialysis takes over that job. Nephrologists are the physicians who decide when to start dialysis, which type is best for a given patient, and how to adjust the treatment over time.
The two main forms are hemodialysis and peritoneal dialysis. Hemodialysis uses a machine to filter blood through an external circuit, typically three times a week at a dialysis center, though home options exist. Peritoneal dialysis uses the lining of the abdomen as a natural filter. A cleansing fluid is cycled in and out through a catheter, and many patients do this at home, often overnight.
Before dialysis begins, the nephrologist coordinates surgical access. For hemodialysis, that usually means creating a connection between an artery and vein in the arm months in advance so it has time to mature. For peritoneal dialysis, a catheter is placed in the abdomen. The nephrologist then monitors labs, adjusts the dialysis prescription, manages complications like infections or fluid overload, and tracks how the patient feels day to day.
Kidney Transplant Care
Nephrologists play a central role before and after a kidney transplant, though the surgery itself is performed by a transplant surgeon. Before transplant, a transplant nephrologist evaluates whether a patient is a good candidate, orders the necessary cardiac, infectious disease, and tissue-matching tests, and manages the waiting list. They also evaluate potential living donors.
After transplant, the nephrologist manages the medications that prevent the body from rejecting the new kidney. These drugs suppress the immune system and require careful, ongoing adjustment. Too little suppression risks rejection; too much increases the risk of infections and certain cancers. The nephrologist monitors kidney function through regular blood work, watches for signs of rejection or complications, and manages the long-term health of the transplanted organ, sometimes for decades.
Nephrologist vs. Urologist
These two specialties overlap when it comes to the kidneys, which creates confusion. The simplest distinction: nephrologists treat kidney diseases using medications, dialysis, and medical management. Urologists are surgeons who operate on the urinary tract and reproductive organs.
If you have chronic kidney disease, protein in your urine, or need dialysis, you’ll see a nephrologist. If you have a large kidney stone that needs surgical removal, a bladder problem, urinary incontinence, prostate issues, or a urological cancer, you’ll see a urologist. Some conditions, like recurrent kidney stones, may involve both specialists: the nephrologist investigates the metabolic cause while the urologist handles any procedures.
Training and Qualifications
Becoming a nephrologist requires a long training path. After medical school, the physician completes a three-year internal medicine residency and earns board certification in internal medicine. Then comes a nephrology fellowship lasting at least 24 months, which includes hands-on training in dialysis, transplant care, kidney biopsies, and managing complex fluid and electrolyte problems. After fellowship, the physician takes a subspecialty board exam through the American Board of Internal Medicine to become a certified nephrologist.
What to Expect at Your First Visit
A first appointment with a nephrologist is largely a conversation and a review of your medical history. Expect the doctor to go through your lab results in detail, especially your GFR, creatinine, and any urine tests. They’ll ask about your medications (some common drugs can harm kidneys), your blood pressure history, family history of kidney disease, and symptoms like swelling, changes in urination, or fatigue.
You’ll likely have blood drawn and provide a urine sample if recent labs aren’t available. The nephrologist may order an ultrasound of your kidneys to check their size and structure. From there, the plan depends on the diagnosis: it might be as simple as adjusting a blood pressure medication, or it could involve more testing, a biopsy, or a referral for dialysis planning. Many kidney conditions are managed with periodic visits every few months rather than frequent appointments, especially in the earlier stages.