Renal biopsy

Generality

Renal biopsy is a diagnostic test that involves the collection of a sample of renal cells, which is then subjected to analysis in the laboratory.

Figure: a renal biopsy depicted in this image taken from the site: aviva.co.uk

The most common procedure is the so-called percutaneous renal biopsy; it is a minimally invasive examination, as it involves the use of a special needle made to penetrate through the skin and carried up to the kidney.

Since percutaneous renal biopsy is contraindicated in some circumstances, it is necessary to subject the patient to some diagnostic tests before being able to perform it.

In most cases, the procedure is safe and uncomplicated. The final results are particularly reliable and full of useful information for the diagnostic classification of the patient.

What is kidney biopsy?

Renal biopsy is a minimally invasive diagnostic test, which consists of collecting and subsequently analyzing a sample of renal cells.

The analysis is not limited to the simple observation under microscope of the cells taken, but also includes their study through various laboratory tests.

The most common renal biopsy procedure, to which this article refers, is the so-called percutaneous renal biopsy ; the term percutaneous indicates the use of a special needle, which is threaded through the skin, exactly at the point where the kidneys are located.

WHERE ARE THE KIDNEYS?

The kidneys reside in the abdominal cavity, on the sides of the last thoracic vertebrae and the first lumbar vertebrae; they are symmetrical and, in shape, resemble a bean.

Their main functions are:

Filter the harmful or foreign waste substances present in the blood and eliminate them with urine
Adjust the hydro-saline and acid-based balance of blood

When you run

Renal biopsy is put into practice when the kidney or kidneys of an individual function in a decidedly inadequate manner. Going into more detail, it is usually performed when:

it is difficult to interpret an individual's kidney problems with non-invasive diagnostic tests;
the doctor needs more information to plan an adequate kidney therapy;
the doctor needs to measure, precisely, the progression of the ongoing kidney disease; for example, in case of renal failure, a biopsy is used to establish the extent of kidney damage;
the doctor wants to know precisely how extensive the damage to the kidney is;
it is necessary to clarify if the treatments for a given kidney disease are giving the desired effects;
the doctor wants to understand the reasons for a possible organ rejection in case of kidney transplantation.

OTHER REASONS

Sometimes, kidney biopsy may be necessary even when certain blood or urine tests are completely abnormal. For example, the presence of blood or protein in the urine ( hematuria and proteinuria, respectively), as well as an excess of waste products in the blood, may justify the use of a renal biopsy.

risks

Renal biopsy is a fairly safe procedure. However, since it is still an invasive procedure, in certain situations it can lead to some complications, such as:

Bleeding . The loss of blood due to the use of the needle is the most common complication of renal biopsy: it manifests itself with hematuria (ie blood in the urine) and lasts a few days. If it should be prolonged or become conspicuous, contact your doctor promptly.
Pain . Feeling a slight pain at the point where the needle was threaded is quite normal and should not alarm; usually it is a passing sensation.
Arteriovenous fistula . The term arteriovenous fistula identifies an abnormal connection between an artery and a vein. In the case of a renal biopsy, it can be created if the needle damages the walls of some adjacent venous and arterial vessels during penetration.
Arteriovenous fistulas following renal biopsy usually resolve on their own and do not cause any particular symptoms.
Infected hematomas . A hematoma is a localized accumulation of blood, following the damage to some blood vessels. Even if it happens very rarely, hematomas that form after a renal biopsy can "host" bacteria and become infected; when this occurs, the patient must immediately undergo antibiotic treatment and surgical drainage to eliminate infected blood.

CONTRAINDICATIONS

Percutaneous renal biopsy is contraindicated in case of:

Inborn tendency to hemorrhages (in this case we speak of hemorrhagic diathesis ).
Severe high blood pressure .
Renal agenesis (ie presence of a kidney only).
Hyperazotemia and uremia .
Certain structural / anatomical abnormalities of the kidneys (eg hydronephrosis, renal cysts, small kidneys, etc.).
Pregnancy.
Urinary tract infections
Obesity.

Preparation

Before performing a renal biopsy, the doctor is required to establish, by means of specific diagnostic tests, whether the patient can undergo the procedure. In case of proven suitability, the same doctor or his assistant will illustrate the guidelines and the fundamental implications of the biopsy test (which drugs to avoid before the exam, when to go back to the last meal etc.).

During this preparatory phase the patient is invited to express any doubts or concerns regarding the procedure.

DIAGNOSTIC EXAMINATION TO ASSESS SUITABILITY?

The main diagnostic tests to assess an individual's suitability for kidney biopsy are: blood tests, urine tests and renal ultrasound.

With blood tests, the states of azotemia and uremia and the coagulation capacity of the blood are evaluated (a blood that hardly coagulates predisposes to bleeding).

With urine tests, however, it is evaluated if there is any infection in the urinary tract.

Finally, with renal ultrasound, it is analyzed if the kidneys show any structural / anatomical anomaly.

WHAT DRUGS CANNOT BE TAKEN BEFORE THE KIDNEY BIOPSY?

If the patient regularly takes antiplatelet agents (aspirin) and anticoagulants (warfarin and heparin), he must stop these assumptions at least two or three weeks before the established date for renal biopsy. Otherwise, he would run the risk of severe bleeding that could even be fatal. To resume administration, you must wait for the go-ahead from the attending physician.

Another category of medications to avoid are NSAIDs, or Non-Steroidal Anti-Inflammatory Drugs.

FAST COMPLETE

Since renal biopsy requires local anesthesia, the patient must present, on the day of the exam, fasting for at least 8 hours (usually from the evening of the previous day).

By complete fasting we mean both abstention from solid food and abstaining from liquids (only water is allowed up to a couple of hours before).

Procedure

Percutaneous renal biopsy, which is in effect an outpatient surgery, is performed as described below. First of all, the doctor puts the patient on his stomach on an operating table.

NB: a patient who has had a kidney transplant is laid down on his back, because the replacement kidney is implanted anteriorly with respect to the classical position.

Figure: a renal biopsy needle (from the site: medind.nic.in)

Figure: ultrasound image of a renal biopsy. The needle is highlighted by the three arrows (from the site: indianjnephrol.org)

Then, with the help of an ultrasound (or a CT scan ), the doctor identifies on the back of the person examined the exact point where to insert the needle (NB in kidney transplants, the same operation is done on the abdomen).

Marked the area, disinfect it and inject the drugs for local anesthesia. As soon as the anesthetic has entered the circle, the doctor makes a small incision on the marked area and puts the needle in it; in order not to make mistakes during the introduction of the needle, it makes use of the "usual" ultrasound machine, also used previously.

Once he has positioned the needle and is ready to aspirate the kidney cells, the doctor asks the patient to hold his breath for a few seconds (the time of the withdrawal, usually 5-10 seconds), in order to keep the kidney in a fixed position (breathing, in fact, moves the kidney up and down). Only at this point does it suck the cells.

Since few renal cells are taken with an aspiration, it is necessary to repeat the whole thing several times: each aspirate is carried out through the same incision and always making the patient hold the breath.

As soon as the doctor thinks the withdrawal is completed, he closes the incised area with stitches and applies a protective bandage.

An alternative procedure to percutaneous renal biopsy: laparoscopic renal biopsy

Individuals suffering from bleeding diathesis or renal agenesis cannot undergo, as we have seen, percutaneous renal biopsy; however, they can undergo an alternative procedure, performed in laparoscopy and called laparoscopic renal biopsy.

AFTER THE RENAL BIOPSY

At the end of the entire biopsy procedure, the patient is seated in a recovery room. Here, it is maintained for several hours under close observation: in fact, it is subjected to continuous monitoring of vital parameters (blood pressure, pulse and breathing) and to blood and urine tests.

Once the effects of local anesthesia have completely vanished and the treating physician has given the green light, the patient can return home.

Maximum rest is recommended for at least 12-24 hours after the exam; therefore, after returning home, any type of fatiguing activity should be avoided.

WHO EXAMINES THE RENAL CELL SAMPLE?

The kidney cells collected are entrusted, as soon as they are taken, to an expert pathologist who, using various laboratory tests, analyzes them and studies their characteristics.

The results are generally available after one week, but in emergencies they can be made available to the patient and the attending physician after 24 hours.