Renal biopsy is an invasive diagnostic technique essential for the treatment of nephrology patients. Through the histological analysis of the renal tissue an etiological diagnosis can be performed, a prognosis can be issued and the therapy of the majority of parenchymal nephropathies can be oriented, both for native kidneys as well as kidney transplants. This latter group also includes protocol biopsies, above all in clinical trials, which merit a separate discussion.
BACKGROUND
This technique was introduced in 1951 by the Danes Iversen and Brun1 through a modification of hepatic puncture-aspiration, technique described by these authors. Guided by pyelography, they performed biopsies on patients in a seated position, obtaining appropriate material in 40% of the cases. Kark et al., introduced changes in 1954. For one, they used a modified Vim-Silverman needle and they also placed the patient in prone position with a pillow under the abdomen. With this, the renal biopsy yield rose to 96%.2 From that time on, although its indications are practically the same, renal biopsy has changed considerably in its technical aspects.
PRACTICAL CONSIDERATIONS
Three types of biopsy can be discerned: percutaneous renal biopsy, open biopsy and transvascular biopsy.
Percutaneous renal biopsy
This is currently the technique of choice. After local anaesthesia, the needle is introduced through the lumbar muscles. As a first option, the left kidney is biopsied (more comfortable for the right-handed operator and far from vital organs) in its lower pole (more accessible). This is the most widespread technique, and requires less personnel, above all in real-time ultrasound-guided modality (only a physician and a nurse).
Open renal biopsy
This procedure involves surgery under general anaesthesia. It consists of the extraction of a wedge of renal tissue. Indicated for uncooperative patients (e.g. small children) and patients with greater risk of haemorrhage (direct haemostasis can be performed). It requires more personnel (surgeon, anesthesiologist, nurse, etc.) and availability of an operating theatre. It is almost obsolete, as it does not really reduce the complications. On the other hand, ultrasound-guided percutaneous biopsy under sedation has become the general practice for children.
Transvascular biopsy
By cannulating a central vein, the renal vein is reached and a small sample of kidney tissue is extracted. This requires certain infrastructure (x-ray room and fluoroscope). It has the disadvantage of venous cannulation and the use of contrast medium. It is indicated in severe coagulation alterations, as it does not perforate the renal capsule, reducing the risk of haemorrhage. Few centres use this technique.3
Other methods such as the transurethral biopsy or laparoscopy are even more unusual.4,5
The most commonly used puncture devices are needles based on the classic Tru-Cut, automatic or semi-automatic, with a 14 G or 18 G calibre. The advantages of automatic biopsy needles over manual ones: the needle remains less time in the kidney, it is autonomous given that just one person is needed to perform the whole biopsy and there is less risk of tearing the kidney tissue. According to our experience and to other authors, the diagnostic yield of both devices is similar, although the risk of complications is less with the automatic needle.6-8 As far as calibre is concerned, we prefer 14 G as it achieves sufficient amount of renal tissue in more than 90% of the biopsies, with just one puncture needed in 80% of them.9
A diagnostic biopsy is considered to be one with sufficient biopsy sample. The number of glomeruli needed varies from one for diffuse nephropathies to 25 for some focal nephropathies. On average, a sufficient biopsy is one that has between 8 and 10 glomeruli; some of them should come from the juxtamedullary region.10
With regard to patient preparation, it is essential to discard the presence of a solitary kidney, polycystic kidney disease, hydronephrosis and small or malformed kidneys. A pre-biopsy renal ultrasound should be performed for this reason. We should check that the blood pressure is controlled and that the coagulation parameters are normal. Although this is debated in medical bibliography,11 we also request the bleeding time test to detect the surreptitious intake of anti-platelet agents (quite common in herbs stores, for example). In the event of it being high, arginine-vasopressin is prescribed to correct this before the biopsy. Likewise, it is essential that the informed consent is signed.
ULTRASOUND-GUIDED RENAL BIOPSY
Until a few years ago, renal puncture was performed blindly, with the subsequent high rate of blank samples and complications.12 With the appearance of imaging techniques (ultrasound and computerised tomography), the drawbacks of blind renal biopsy have been mostly eliminated. Real-time ultrasound-guided renal biopsy is currently a consolidated technique. It has obvious advantages with regards to tomography. Besides not posing a risk of radiation for the patient, it offers better availability, making it possible to perform «bedside” biopsy. It is far more economical and does not need the use of contrast media. As it allows for continuous visualisation of the needle’s position in the renal parenchyma, as well as its placement in the required renal area, the professional who handles it is not taking any risk. The biopsy time is also shortened, from approximately 30 minutes in the case of tomography to 10-15 with the ultrasound.
Real-time ultrasound-guided biopsy requires experience in handling US, since the selection, locating the puncture point and viewing the needle tip can sometimes be quite difficult (obese, senile or uncooperative patients, small or cystic kidney). At present, with the incorporation of ultrasounds to renal biopsy, obtaining sufficient diagnostic material is over 90% in most series.13-15 Diagnostic yield depends on the professional’s skill in handling the needle and placing it as superficially as possible to take a sample exactly from the cortex.14-18 The incidence of biopsy complications has been reduced from approximately 10% with a blind technique to 2-6% with an ultrasound-guided.19-21
The usual post procedure hospital monitoring period is 24 hours. With the new technology (automatic needles and ultrasound monitoring), renal biopsy has become a low risk procedure, so some authors recommend it as an outpatient procedure with only 6-8 hours of hospital bed rest after the biospsy.22,23 A recent study shows that this practice is not recommendable, given that 33% of prematurely discharged biopsy patients suffer complications.20
An article by Dr. Toledo et al.24 reviews their experience with 867 native kidney renal biopsies over 18 years. They performed a retrospective study of 797 biopsies with a 0.75% rate of major complications and a prospective analysis over one year of 70 renal biopsies where they recorded major complications (1.4%) as well as minor complications (2%). Since post biopsy ultrasounds were performed only on patients with clinical results, some minor complications such as asymptomatic haematoma (< 2cm in diameter) or obstruction of the transitory route with clots were not included in this series.9,20 All the major complications appeared in patients with substrate favourable to bleeding. The procedure’s yield was good. This paper is of great interest as it deals with a broad series of ultrasound-guided biopsies performed by nephrologists and due to the low rate of complications that compares favourably with publications in major international journals, above all if the fact that half the patients had kidney failure, a known risk factor for bleeding, is taken into account.25-27
We are pleased that Spanish nephrologists are including ultrasounds in their daily tasks more and more, a practice that our department has advocated for a number of years.28, 29
KEY CONCEPTS
1. Renal biopsy is an essential diagnostic technique in handling the nephrological patient.
2. Real-time ultrasound-guided renal biopsy with automatic needle has decreased the complication rate.
3. With the inclusion of ultrasound to nephrology, the nephrologist has recovered his main role in performing renal biopsy.
4. After the biopsy, a systematic ultrasound should be performed to avoid infradiagnosis of complications.
5. The bed rest period after biopsy should be 24 hours.
