Kidney mass biopsy

A needle test, done through the skin of your back or side with CT or ultrasound guidance, that takes a few thin samples of a kidney mass to find out what it is.

Also called renal mass biopsy, renal tumor biopsy, kidney tumor biopsy, core needle biopsy of the kidney, percutaneous renal biopsy, CT-guided kidney biopsy, ultrasound-guided kidney biopsy, needle biopsy of kidney mass

Where: Hospital radiology department (CT or ultrasound room)
Anesthesia: Local numbing, often with light sedation through an IV
Time in the room: About 30 to 60 minutes in the room
Hospital stay: Same day; you rest and are watched for about 2 to 4 hours afterward
Back to normal: 1 to 2 days
Back to work: Usually the next day

See the steps

TumorKidneyFat (Gerota's fascia)Skin

Where it happens. The highlighted part is what this procedure treats.

Overview

A kidney mass biopsy uses a thin hollow needle passed through the skin of your back or side to take a few small samples, called cores, from a lump in the kidney. A radiologist, a doctor who specializes in imaging, usually does it with a CT scan or ultrasound to guide the needle. You are awake but numbed, and often given medicine to relax.

Not every kidney mass is cancer. About 1 in 5 small solid kidney masses turns out to be benign. A biopsy can show whether a mass is cancer, which type it is, and sometimes how aggressive it looks. That information can change the plan, for example between watching the mass with scans, freezing it, or surgery.

This is different from the medical kidney biopsy that kidney doctors use to diagnose kidney disease. This page is about biopsy of a lump or tumor.

A biopsy is not always needed. Many people with a mass that looks like cancer on a CT or MRI go straight to surgery, because the operation both treats and diagnoses it. Your urologist will suggest a biopsy when the result is likely to change your treatment.

The parts of your body involved

Your kidneys sit high in the back of your belly, under the lower ribs, with the bowel in front and the back muscles behind. Each is wrapped in fat. A needle from the back can reach most kidney masses without passing through the bowel. The outer layer of the kidney, the cortex, is where most kidney tumors start. The kidney has a rich blood supply, which is why bleeding is the main thing your team watches for afterward.

Kidney mass
The lump being sampled. It may be cancer, a benign tumor, or something else.
Cortex
The outer layer of the kidney, where most tumors start.
Fat around the kidney
A cushion of fat the needle passes through.
Skin and back muscles
The needle enters here, after numbing.

Why it’s done

A biopsy is most useful when knowing exactly what the mass is would change what you do next.

Choosing between watching and treating
A benign or slow-growing result may support watching a small mass with scans instead of treating it.
Before ablation
Since ablation does not remove the tumor, a biopsy is the only way to know what was treated.
History of another cancer
A kidney mass could be spread from another cancer, which is treated differently.
Possible lymphoma or infection
These are treated with medicines, not kidney surgery.
Cancer that has spread
Knowing the exact kidney cancer type helps choose the right medicines.

Other options

Going straight to treatment
If the mass looks clearly like cancer and you would choose surgery whatever the biopsy showed, many surgeons skip the biopsy. The removed tumor is then examined in full.
Watching with scans
For very small masses, especially in older people, repeated scans to measure growth may be enough without a biopsy.
Biopsy during ablation
If you are having ablation, the biopsy can be done at the start of the same visit instead of separately.

Getting ready

Tick items off as you go. Your checklist is saved on this device only.

1 to 2 weeks before

Blood thinners

Tell your team about aspirin, clopidogrel, warfarin, apixaban, rivaroxaban or any blood thinner. They will tell you if and when to stop. Never stop a heart stent medicine without asking the doctor who prescribed it.

Supplements and pain pills

Stop ibuprofen, naproxen, fish oil, vitamin E and herbal supplements for about 5 to 7 days if your team asks.

Blood tests

A blood count and clotting tests are checked before the biopsy.

The day before

Fasting

If you will receive sedation, you will usually be asked not to eat for about 6 hours before, with clear liquids allowed until a couple of hours before. Follow your instructions.

Arrange a driver

You cannot drive yourself home after sedation.

Diabetes medicines

Ask how to adjust insulin or diabetes pills while fasting.

The morning of

Medicines

Take approved medicines, such as blood pressure pills, with a sip of water.

Check-in

A nurse places an IV and checks your blood pressure. High blood pressure may be treated before the biopsy to lower bleeding risk.

Consent

The radiologist explains the plan and risks and answers questions.

In the operating room, step by step

Press play or pick a step. Each drawing shows what your surgeon is doing at that moment. Your team may do some steps differently.

YouScrub nurseVideo screen

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1. Lying on the table

You lie face down or on your side on the CT or ultrasound table, with pillows for comfort. A nurse connects monitors for your heart, blood pressure and oxygen, and may give relaxing medicine through your IV.

You lie face down or on your side on the CT or ultrasound table, with pillows for comfort. A nurse connects monitors for your heart, blood pressure and oxygen, and may give relaxing medicine through your IV.
A few CT pictures or an ultrasound show the mass. The radiologist picks the safest straight path from your skin to the mass, avoiding the bowel, lung and large blood vessels, and marks the spot on your skin.
The skin is cleaned with a cold antiseptic and numbed with local anesthetic, which stings for a few seconds. The deeper tissue along the path is numbed too. A tiny nick is made in the skin.
A thin guide needle is moved in small steps toward the mass, with scans checking its position each time. You may be asked to hold your breath at the same point each time, because the kidney moves when you breathe.
More detail
Most radiologists use a coaxial technique: a slightly larger outer needle stays in place at the edge of the mass, and the biopsy needle passes through it several times. This means the skin and muscle are crossed only once.
A spring-loaded biopsy needle takes a thin core of tissue, about the size of a short piece of pencil lead. You will hear a click and may feel a brief push or pressure. Usually 2 to 4 cores are taken.
More detail
Samples are taken from the solid, living parts of the mass and avoid areas that look like dead tissue on the scan. For a mass with a cystic part, the needle aims at the solid part.
The needle is removed and a final scan checks for any bleeding around the kidney. Pressure is held on the skin and a small bandage is placed.
You lie still for about 2 to 4 hours while nurses check your blood pressure, pulse, the bandage, and your urine for blood. If all is well, you go home the same day.

After the operation

Right afterward

Bed rest
Lie quietly for 2 to 4 hours, often on the side that was biopsied, which presses on the area.
Vital signs
Nurses check your blood pressure and pulse often.
Urine
Your first urine is checked for blood. A little pink is common.
Going home
You go home with a driver once you are stable, walking and urinating.

At home

Rest the first day
Take it easy for the rest of the day and the night.
Pain
Mild soreness at the biopsy site for a day or two. Use acetaminophen. Avoid ibuprofen, naproxen and aspirin for a few days unless your doctor says otherwise.
Bandage
Remove it after 24 hours. You can shower then; avoid baths for a few days.
Urine
Light pink urine for a day can be normal. Drink fluids.
Activity
Avoid heavy lifting, hard exercise and contact sports for about 1 week.
Blood thinners
Restart them only when your team tells you, often 1 to 2 days after the biopsy.
Driving and work
No driving for 24 hours after sedation. Most people return to work the next day.

Recovery timeline

Day of biopsy
Biopsy and rest
About an hour in the room and a few hours of observation, then home.
Day 1 to 2
Back to normal
Soreness fades and most people go back to work.
3 to 7 days
Results
The pathology report is usually ready within a week. Some tumors need extra special stains, which can add a few days.
About 1 week
Full activity
Heavy lifting and hard exercise can usually resume.
1 to 2 weeks
Results visit
You meet your urologist to discuss what the mass is and the next step.
Weeks to months
Next step
Depending on the result: scans, ablation, surgery, or medicines.

What it feels like

Most people describe the biopsy as easier than they expected. The hardest part is often the wait for the result.

Before the biopsy
Worry about pain, about needles near the kidney, and about what the result will show.
What helpsAsk for relaxing medicine. Ask when and how you will get the result, and who will explain it.
The numbing shot
A sharp sting and burning for a few seconds, then numbness.
What helpsSlow breathing helps. Tell the team if you feel sharp pain later so they can add more numbing.
Each sample
A loud click from the biopsy device and a brief push or deep pressure. Holding your breath on command can feel tiring.
What helpsThe team will warn you before each click. Each one is over in a second.
Lying still afterward
Boredom and a stiff back from lying still for hours.
What helpsBring something to listen to. Ask the nurse to adjust your pillows.
Waiting for results
Many people find these days the hardest part.
What helpsPlan something to do. Remember that a result of benign or a slow-growing cancer is common for small masses.

How well it works

A successful biopsy gives a clear diagnosis that helps you and your team choose the next step.

A clear answer most of the time
In experienced centers, about 9 in 10 biopsies give a clear diagnosis. When a diagnosis is made, it is very accurate at telling cancer from not cancer.
Type of tumor
The report may say clear cell, papillary or chromophobe kidney cancer, a benign tumor such as an oncocytoma or angiomyolipoma, or something else such as lymphoma.
Grade is less certain
A small sample may not show the most aggressive part of the tumor, so the grade on a biopsy can be lower than the true grade.
Nondiagnostic does not mean benign
About 1 in 10 biopsies does not get enough useful tissue. This is not the same as a benign result. A repeat biopsy usually gives an answer.

Risks

Every operation has risks. These are the ones people ask about most, with honest odds where good numbers exist. Your surgeon’s own results matter more than averages.

Common

Soreness at the biopsy site

Mild and short-lived.

Small bleed around the kidney

Often seen on the final scan. Almost always stops on its own and needs no treatment.

Blood in the urine

Light pink urine for a day is common.

Less common

Nondiagnostic resultAbout 1 in 10 biopsies

Not enough useful tissue to make a diagnosis. A repeat biopsy may be needed.

Heavier blood in the urine

Usually settles with fluids and rest.

Vasovagal reaction

Feeling faint or sweaty during or after the procedure. It passes with lying flat and fluids.

Rare

Bleeding needing a transfusion or procedureFewer than 1 in 100 people

Rare. A bleeding vessel can be blocked through a thin catheter if needed.

Collapsed lung

Rare, with masses near the top of the kidney.

Infection

Rare.

Tumor cells along the needle path

Extremely rare with modern techniques.

Call your care team or go to the emergency room if

Bright red urine or clots, or blood in the urine that gets heavier instead of lighter
Feeling faint, dizzy, or a racing heart
Severe or worsening pain in the back, side or belly
Fever of 101°F (38.3°C) or higher, or chills
Shortness of breath or chest pain (call 911)
Unable to urinate

Questions to ask your surgeon

Will the biopsy result change what we do?
Who will do the biopsy, and with CT or ultrasound?
Will I be awake? Can I have something to relax?
When should I stop and restart my blood thinner?
How many samples will you take?
When will results be ready, and who will call me?
What happens if the result is nondiagnostic?
What happens next if it is cancer, or if it is benign?

Words you may hear

Biopsy: Taking a small sample of tissue to look at under a microscope.
Core: A thin cylinder of tissue taken by a biopsy needle.
Percutaneous: Through the skin, with a needle rather than a surgical cut.
Coaxial technique: Using an outer guide needle so the biopsy needle can pass through it several times.
Radiologist: A doctor who specializes in imaging and image-guided procedures.
Pathologist: A doctor who examines tissue under a microscope and writes the diagnosis.
Oncocytoma: A common benign kidney tumor that can look like cancer on scans.
Angiomyolipoma: A benign kidney tumor made of blood vessels, muscle and fat.
Nondiagnostic: A biopsy that did not get enough useful tissue to make a diagnosis.
Grade: How abnormal cancer cells look, which hints at how aggressive the tumor is.

Common questions

Does a biopsy spread cancer?

This is extremely rare with modern techniques, especially when an outer guide needle is used. The benefit of a clear diagnosis usually far outweighs this risk.

Will it hurt?

The numbing shot stings briefly. During the biopsy most people feel pressure and hear a click, but not sharp pain. Some soreness afterward is common for a day or two.

If the biopsy is benign, can I skip treatment?

Often yes, though some benign-looking results still need follow-up scans, because some tumors contain mixed cell types. Your urologist will advise you.

Why didn't my surgeon suggest a biopsy?

If a mass looks like cancer and surgery would be recommended whatever the biopsy showed, the operation itself gives the diagnosis. A biopsy is most helpful when the result could change your plan.

What if the biopsy does not give an answer?

A repeat biopsy usually does. Your team may also choose to watch the mass with scans or go ahead with treatment based on how it looks.

Sources this page draws on

American Urological Association, Renal Mass and Localized Renal Cancer: Evaluation, Management, and Follow-up: AUA Guideline (2021)
European Association of Urology, EAU Guidelines on Renal Cell Carcinoma
European Urology, Systematic review and meta-analysis of the diagnostic accuracy of percutaneous renal tumour biopsy (Marconi et al.) (2016)
American Cancer Society, Tests for Kidney Cancer

Written November 2026. This page explains what usually happens. It is not medical advice and does not replace a conversation with your own surgeon, whose plan for you comes first.