Renal Biopsy

Generality

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

Figure: A kidney biopsy depicted in this "image from the site: aviva.co.uk

The most common procedure is the so-called percutaneous kidney biopsy; this is a minimally invasive examination, since it involves the use of a special needle made to penetrate through the skin and brought up to the kidney.
Since percutaneous renal biopsy is contraindicated in some circumstances, it is necessary to undergo some diagnostic tests before it can be performed.
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 the collection, and subsequent analysis, of a sample of kidney cells.

The analysis is not limited to the simple observation under the microscope of the cells taken, but also provides for their study through various laboratory tests.
The most common kidney biopsy procedure to which this article refers is the so-called percutaneous kidney biopsy; the term percutaneous indicates the use of a special needle, which is inserted through the skin, exactly in the point where the kidneys are located.

WHERE ARE KIDNEYS FOUND?

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

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

When you do

Kidney biopsy is done when an individual's kidney or kidneys are functioning in a decidedly inadequate way. 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 further information in order to plan adequate renal therapy;
the doctor needs to accurately measure the progression of the ongoing kidney disease; for example, in the case of kidney 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 whether the treatments for a given kidney disease are giving the desired effects;
the doctor wants to understand the reasons for organ rejection in the event of a kidney transplant.

OTHER REASONS

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

Risks

Kidney 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:

Hemorrhages. Blood loss due to the use of the needle is the most common complication of kidney biopsy: it manifests itself as hematuria (ie blood in the urine) and lasts a few days. If it lasts longer or becomes conspicuous, you should contact your doctor promptly.
Ache. Feeling a little pain where the needle was threaded is quite normal and shouldn't be alarming - usually a passing sensation.
Arteriovenous fistula. The term arteriovenous fistula identifies an "abnormal connection between" an artery and a vein. In case of renal biopsy, it can be created if the needle, during penetration, damages the walls of some adjacent venous and arterial vessels.
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 injury to certain blood vessels. Even if it happens very rarely, the hematomas that form after a kidney biopsy can "host" bacteria and become infected; when this occurs, the patient must immediately undergo antibiotic treatment and surgical drainage to clear the infected blood.

CONTRAINDICATIONS

Percutaneous renal biopsy is contraindicated in case of:

Innate tendency to bleed (in this case we speak of hemorrhagic diathesis).
Severe blood hypertension.
Renal agenesis (i.e. the presence of only one kidney).
Hyperazotemia and uremia.
Certain structural / anatomical abnormalities of the kidneys (e.g. hydronephrosis, renal cysts, small kidney etc).
Pregnancy.
Urinary tract infections
Obesity.

Preparation

Before performing a kidney 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 examination (which drugs to avoid before the examination, when the last meal has to be found, etc.).
During this preparatory phase the patient is invited to express any doubts or concerns regarding the procedure.

DIAGNOSTIC TESTS TO ASSESS THE SUITABILITY €

The main diagnostic tests to evaluate the suitability of an individual for renal biopsy are: blood tests, urine tests and kidney ultrasound.
With blood tests, the states of azotemia and uremia and the coagulation capacity of the blood (a blood that coagulates poorly predisposes to bleeding) are assessed.
Urine tests, on the other hand, assess whether there is any infection in the urinary tract.
Finally, with renal ultrasound, it is analyzed if the kidneys show any structural / anatomical anomaly.

WHICH DRUGS SHOULD NOT BE TAKEN BEFORE KIDNEY BIOPSY?

If the patient regularly takes antiplatelet agents (aspirin) and anticoagulants (warfarin and heparin), he should stop these intakes at least two to three weeks before the established date for the renal biopsy. Otherwise, you run the risk of severe bleeding that could even be fatal. To resume administration, you must wait for the go-ahead from the treating physician.
Another category of drugs to avoid are NSAIDs, or Non-Steroidal Anti-Inflammatory Drugs.

FAST FULL

Since the renal biopsy requires local anesthesia, the patient must have been fasting for at least 8 hours on the day of the examination (usually from the evening of the previous day).
By complete fasting, we mean both the abstention from solid food and the abstention from liquids (only water is allowed up to a couple of hours before).

Procedure

Percutaneous renal biopsy, which is effectively an outpatient surgery, is performed as described below. First, the doctor makes the patient lie on his stomach on an operating room table.

N.B: a patient whose kidney has been transplanted is made to lie on his stomach, because the replacement kidney is implanted anterior to the classic position.

Figure: A kidney biopsy needle (from site: medind.nic.in)

Figure: Ultrasound image of a kidney 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 (N.B in kidney transplant recipients, the same operation is done on the abdomen).
Once the area has been marked, he disinfects it and injects it with drugs for local anesthesia. As soon as the anesthetic has entered the circulation, the doctor makes a small incision on the marked area and inserts the needle into it; so as not to make mistakes during the procedure. introduction of the needle, makes use of the "usual" ultrasound, also used previously.
Once he has positioned the needle and is ready to aspirate the kidney cells, the doctor asks the patient to hold their breath for a few seconds (the time of sampling, 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, it aspirates the cells.
Since a few kidney cells are removed with an aspiration, it is necessary to repeat everything several times: each aspiration is carried out through the same incision and always making the patient hold his breath.
As soon as the doctor considers the collection completed, he closes the incised area with sutures and applies a protective bandage.

An alternative procedure to percutaneous kidney biopsy: laparoscopic kidney biopsy

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

AFTER KIDNEY BIOPSY

At the end of the entire biopsy procedure, the patient is made to sit in a hospitalization room. Here, he is kept under close observation for several hours: in fact, he is subjected to continuous monitoring of vital parameters (blood pressure, pulse and respiration). and blood and urine tests.
Once the effects of the local anesthesia have completely worn off, and the attending physician has given the green light, the patient can return home.

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

WHO TESTS THE KIDNEY CELL SAMPLE?

The kidney cells collected are entrusted, as soon as they are taken, to an expert pathologist who, by means of various laboratory tests, analyzes them and studies their characteristics.
The results are usually available after one week, but in emergency cases they can be made available to the patient and the treating physician as early as 24 hours.