The percutaneous native kidney biopsy : a nephrologist ’ s perspective

Introduction Kidney biopsy is one of the most important diagnostic tools in a nephrologist’s armamentarium. It has been shown that performance of a kidney biopsy in the appropriate clinical setting has the potential to alter the clinical diagnosis as well as change the therapy in many cases. Current biopsy practice is very safe with minimal complications and has the ability to obtain adequate tissue for histological diagnosis in more than 95% of cases. It is important for nephrologists to know about the various indications, contraindications and modifications in the procedure as well as the complications. All the trainees are supposed to learn the proper technique of kidney biopsy not only because of the importance of the procedure, but because of the fact that kidney biopsy is one of the triggers that enable the development of nephrology as a separate subspecialty. In this article, we critically review various aspects of a kidney biopsy that is important for practice by nephrologists. Conclusion Percutaneous kidney biopsy is a relatively safe procedure because of the development of many advances like ultrasound-guided and automated biopsy needles. Complication rates following the procedure are minimal and have been decreasing over a period of time. Introduction The procedure of obtaining the renal tissue for histopathological examination, ‘the kidney biopsy’, is perhaps one of the turning points in nephrology practice that enabled it to develop as a separate subspecialty1. The widespread acceptance and performance of this procedure has been brought about by refinements in the existing practices and introduction of newer developments. This has led to a more successful tissue yield that resulted in a more accurate histological diagnosis and has also made the procedure reasonably safe. The kidney biopsy is used for evaluation of many renal diseases and occasionally becomes the only answer to many complex disorders. The aim of this critical review is to discuss the native kidney biopsy through a nephrologist’s perspective. Discussion In this review, the authors have referenced some of their own studies. These referenced studies have been conducted in accordance with the Declaration of Helsinki (1964) and the protocols of these studies have been approved by the relevant ethics committees associated to the institutions in which they were performed. All human subjects, in these referenced studies, gave informed consent to participate in the studies. Evolution of the biopsy procedure The earliest histological examinations of the renal tissue were secondary to examination of tissues obtained during renal decapsulation procedures performed between 1900 and 19301. Kidney biopsy as an acceptable and valid medical procedure started to evolve following the seminal work published by Iverson and Brun2 in 1951 and Alwall3 in 1952. These initial reports were aspiration biopsies performed with the patient in the sitting position and using imaging (X-ray or intravenous pyelogram) for surface marking of the kidney. Adequate tissue collection in these two initial reports was found to be only 50% and 77%, respectively. In 1954, Kark and Muehrcke used an exploring needle to localise the kidney after placing the patient in the prone position and used the Franklin-modified Vim-Silverman needle for biopsy. The technique used by them can be described as a ‘blind procedure’4. This modification resulted in development of more successful biopsies and a larger core of tissue for examination. Subsequently imaging modalities have been used for localising the kidneys and ultrasound-guided (USG) is used most commonly. Initially used for surface marking and approximating the needle direction and depth, the USG has gradually been adopted to conduct the entire biopsy procedure under real-time guidance. Biopsies conducted under the USG management are safer than a blind procedure and can also result in more successful biopsies with a better tissue sample5,6. Th e automated biopsy devices In the 1980s, the spring loaded, automated, cutting-needle biopsy guns were developed7. The advantages of safety, better tissue yield with minimal tissue disruption and ease of the procedure enabling use of a real-time USG imaging with one hand and the biopsy gun with another, made these automated devices readily acceptable and the Tru-Cut needles were gradually phased out8–12. Adequate tissue for a Di ag no si s * Corresponding author Email: drvgolay@gmail.com Department of Nephrology, Institute of Postgraduate Medical Education and Research, 244 AJC Bose Road, Kolkata, India-20


Introduction
The procedure of obtaining the renal tissue for histopathological examination, 'the kidney biopsy', is perhaps one of the turning points in nephrology practice that enabled it to develop as a separate subspecialty 1 .The widespread acceptance and performance of this procedure has been brought about by refinements in the existing practices and introduction of newer developments.This has led to a more successful tissue yield that resulted in a more accurate histological diagnosis and has also made the procedure reasonably safe.
The kidney biopsy is used for evaluation of many renal diseases and occasionally becomes the only answer to many complex disorders.The aim of this critical review is to discuss the native kidney biopsy through a nephrologist's perspective.

Discussion
In this review, the authors have referenced some of their own studies.These referenced studies have been conducted in accordance with the Declaration of Helsinki (1964) and the protocols of these studies have been approved by the relevant ethics committees associated to the institutions in which they were performed.All human subjects, in these referenced studies, gave informed consent to participate in the studies.

Evolution of the biopsy procedure
The earliest histological examinations of the renal tissue were secondary to examination of tissues obtained during renal decapsulation procedures performed between 1900 and 1930 1 .Kidney biopsy as an acceptable and valid medical procedure started to evolve following the seminal work published by Iverson and Brun 2 in 1951 and Alwall 3 in 1952.These initial reports were aspiration biopsies performed with the patient in the sitting position and using imaging (X-ray or intravenous pyelogram) for surface marking of the kidney.Adequate tissue collection in these two initial reports was found to be only 50% and 77%, respectively.In 1954, Kark and Muehrcke used an exploring needle to localise the kidney after placing the patient in the prone position and used the Franklin-modified Vim-Silverman needle for biopsy.The technique used by them can be described as a 'blind procedure' 4 .This modification resulted in development of more successful biopsies and a larger core of tissue for examination.
Subsequently imaging modalities have been used for localising the kidneys and ultrasound-guided (USG) is used most commonly.Initially used for surface marking and approximating the needle direction and depth, the USG has gradually been adopted to conduct the entire biopsy procedure under real-time guidance.Biopsies conducted under the USG management are safer than a blind procedure and can also result in more successful biopsies with a better tissue sample 5,6 .

Th e automated biopsy devices
In the 1980s, the spring loaded, automated, cutting-needle biopsy guns were developed 7 .The advantages of safety, better tissue yield with minimal tissue disruption and ease of the procedure enabling use of a real-time USG imaging with one hand and the biopsy gun with another, made these automated devices readily acceptable and the Tru-Cut needles were gradually phased out [8][9][10][11][12] .Adequate tissue for a successful diagnosis can now be obtained using a real-time USG guidance and automated biopsy needles in more than 95% of cases 13 .
A variety of sizes of these automated devices are generally manufactured, but only 14 gauges through 18-gauge devices have been traditionally used for kidney biopsies.It is generally seen that bleeding complications are observed more often with a 14-gauge needle, without any additional advantage regarding the adequacy of the tissue 14 .A 16-gauge device has an internal diameter that is approximately thrice the diameter of an adult glomerulus and thus, could theoretically result in a better glomerular yield with lesser 'fragmented' glomeruli and lesser number of cores.The safety of the 16-gauge needle has also been shown to be as good as the smaller 18-gauge needle 15,16 .Thus, it is advisable to use a 16-gauge needle for adults and an 18-gauge needle for children.The larger 14-gauge needle is not recommended for a kidney biopsy.

Percutaneous kidney biopsy procedure
Even though kidney biopsy is a relatively safe procedure, it is still an invasive one and should be performed only when indicated.Even then its importance cannot be undermined.This is because performing a kidney biopsy has been shown to change the pre-biopsy clinical diagnosis in 44% of cases and has also been shown to change therapy in 30% of cases 17 .Thus, a kidney biopsy can be very aptly labelled as a 'necessary evil'.
The indications of a kidney biopsy include a diverse spectrum of illnesses (Table 1).However, the choice of patients depends on the prevalent practices and is not absolute.For example, even though a kidney biopsy is considered necessary in all adult nephrotic syndrome patients, it is performed only in selected childhood cases e.g., in steroid-resistant or atypical cases.Similarly, in cases where the renal function has acutely worsened, the need and timing of a kidney biopsy depends on various factors like presence of a correctable underlying cause, manifestations of systemic diseases, unsatisfactory recovery etc.

Pre-biopsy evaluation
A proper history and a good physical examination is a must in all patients.Laboratory examinations that are essential before biopsy include a complete blood count, complete biochemical test, coagulation parameters [activated partial thromboplastin time (APTT), prothrombin time (PT), bleeding time and clotting time] and urinalysis.In addition, further tests have to be performed according to the underlying renal syndrome.All patients should have a USG examination, which is mainly to rule out small kidneys or any anatomic abnormalities or other contraindications to biopsy.
There is a lot of controversy surrounding kidney biopsy in patients with deranged coagulation function test (PT and APTT).Abnormal coagulation test did not predict increased bleeding risks in many clinical situations, including kidney biopsy according to a systematic review 18 .In a recent literature review by Jecko Thachil 19 , bleeding risk from the abnormal clotting screen was minimal in the absence of prior bleeding history in patients with renal disease.Administration of fresh frozen plasma (FFP) in these cases is probably unnecessary and often causes delay in the procedure.Similarly, platelet transfusions may not be appropriate in those with platelet dysfunction.The author of this review concluded that patients without any prior bleeding history and with PT/APTT less than 1. include thrombin generation tests or thromboelastography methods before considering FFP transfusions.Large trials are required to investigate the extent to which deranged coagulation tests along with renal dysfunction predicts bleeding following kidney biopsy and probably, this will remain only a myth.
After selecting and investigating the patients who require a kidney biopsy, it is imperative to look for various situations where performing a biopsy is contraindicated or requires special modifications in the procedure (Table 1) 20,21 .The aim should be to always control many of these contraindications before a biopsy is performed.In certain situations, it becomes necessary to perform a biopsy urgently regardless of these circumstances when some alternate strategies like open (surgical) biopsy, transjugular (transvenous) biopsy and laparoscopic biopsy can be used 21 .

Performing a percutaneous native kidney biopsy
After the patient has been selected and evaluated, an informed consent is taken (from the guardian in case of minors).The patient is instructed to lie prone with a pillow below the abdomen at the level of the umbilicus.A preliminary USG is performed to localise the surface marking of the position of the lower urinary pole.We routinely perform renal biopsies from the left kidney by default as it is away from the major vessels and organs and it is easier to handle the biopsy guns in case of right-handed operators.The skin is then cleaned with povidone-iodine/chlorhexidine and is draped with a sterile sheet.The USG probe is covered with a sterile cover and is placed on the skin after applying some sterile jelly.It is generally enough to perform the procedure under local anaesthesia.Occasionally, in children or in anxious individuals, mild sedation can be used.Local anaesthesia in the form of 1%-2% lignocaine is injected under USG guidance from the skin, down to the renal capsule, along the biopsy tract.
The appropriate biopsy needle is then advanced under USG guidance along the anesthetised tract.We prefer a 16-gauge biopsy needle for adults and 18-gauge needle for children as described above.Before the renal capsule is reached, the patient is instructed to take a deep inspiration and hold it such that the lower pole comes under the needle tip, and then it is advanced with the needle passing the capsule and after this the triggering mechanism of the needle is released.The needle is then withdrawn immediately and the patient is instructed to start breathing.In general, 2 to 3 cores of tissue are sufficient for an adequate yield.
The biopsy sample is then inspected under either a dissecting microscope or under a light microscope by making a wet mount of the core with normal saline with or without a cover slip.This is essential to ensure that the sample contains an adequate number of glomeruli, which can be seen as reddish dots.If this facility is not available, then the individual cores can be divided.One acceptable protocol for this is to send the terminal 1 mm from both sides of the biopsy core for electron microscopy (EM).The remaining sample is then divided and the larger of the first and smaller of the second core is sent for light microscopy (LM) and the remaining tissue is used for immunofluorescence (IF) 22 .Samples should be handled with extreme care to avoid development of artefacts.Desiccation of the sample should be avoided and normal saline should be used to wash off the tissue cores from the biopsy needle, which should be placed on saline soaked gauze rather than dry or water soaked gauze.An 18-gauge needle of a wooden stick should then be used to handle the samples and if they are divided, the scalpel should be fresh and sharp.The samples are then placed in fixatives and transport media for LM, IF and EM, and are dispatched immediately along with the relevant clinical and laboratory details.

Post-biopsy observation
After the biopsy, strict bed rest lying flat on the back is advised for 6 to 8 hours and patients are generally restricted to bed for the next 24 hours.The duration of the strict bed rest is unclear, but in one study decreasing this period of strict bed rest from 7 to 2 hours decreased the incidence of back pain without increasing the complication rate 23 .Vitals are frequently monitored and every voided urine sample is examined for visible haematuria and patients are observed for any complications.
Due to the occurrence of delayed bleeding complications, kidney biopsy is generally performed as an inpatient procedure as it is believed that ≥33% complications occur beyond 8 hours of observation 24,25 .However, there are many studies conducted in both adult and paediatric populations [26][27][28][29][30] , including our own experience 31 , where a shorter observation time enabled an outdoor procedure that was safe and reported no deaths.This can also prove to be cost effective.Maripuri et al. 32 have reported that the overall cost was much lower for outpatient biopsies compared with inpatient observation even when the additional costs accounted for the treatment of complications or possible death was considered.
Performing additional tests such as haemoglobin, haematocrit or USG as a routine for all patients may not be cost effective.Waldo et al. 33 showed that on a 1-hour post-biopsy USG, absence of a perirenal haematoma predicted no complications, but presence of one also could not significantly predict the development of complications.Thus, careful clinical observation is good enough.

Complications
The current practice of percutaneous native kidney biopsy is a relatively safe procedure with life threatening complications occurring in <0.1% of biopsies 13,24,34,35 .Complications are generally divided into those that resolve spontaneously without interventions (minor complications) and those that require interventions-like transfusions or invasive procedures or are life or organ threatening (major complications) (Table 2).
Significant macroscopic haematuria has been variably reported from 0.3%-14.5%,but a recent meta-analysis of 34 studies from 1980 till 2011 comprising 9,474 biopsies showed that the overall rate was 3.5% with 0.9% requiring blood transfusions and angiographic intervention is only 0.6% 14 .New data from the Norwegian Kidney Biopsy Registry show that this complication rate may still be lower with macroscopic haematuria reported in 1.9% of the patients; 0.9% of patients requiring blood transfusion and 0.2% of patients requiring surgical intervention/catheterisation 36 .
Multiple factors have been considered predictive of complications after biopsy.However, a meta-analysis showed that out of the many variables considered, a higher blood transfusion requirement was observed when a 14-gauge needle was used for biopsy compared with 16-gauge and 18-gauge needles, in patients with higher serum creatinine values, in biopsies performed for acute kidney injury, lower baseline haemoglobin and also in older patients and hypertensives 14 .Another study showed that biopsies in patients with a serum creatinine ≥5.0 mg/dL were 2.3 times more likely to have a complication after renal biopsy 25 .

Th e non-invasive kidney biopsy?
There are many limitations of a kidney biopsy.The non-uniform parenchymal involvement in many renal diseases, which can be missed by biopsy taken from a very small section of the kidney, might miss detection of the pathological changes.Many times, there are situations, when a biopsy cannot be safely performed or can result in complications.A noninvasive method of assessment is the urinary proteomics, which is study of the protein profile in the urine using complicated procedures, like liquid chromatography and tandem mass spectrometry.The precursor peptides and fragment ion masses are analysed by complex search programmes to identify proteins from genomic databases 37 .This can serve as a theoretically sound alternative to a kidney biopsy, but is still in the developmental stage.Till this new method becomes one of the validated and economically acceptable methods, the percutaneous kidney biopsy is here to stay.

Conclusion
Percutaneous kidney biopsy is one of the most important investigations in clinical nephrology and is a relatively safe procedure because of the development of many advances such as USG and automated biopsy needles.Complication rates following the procedure are minimal and have been decreasing over a period of time.It is important that all nephrology programmes train the trainees in performing biopsies, so that there is a wider clinical use of this important investigation.

Table 1 . Indica ons and contraindica ons of percutaneous na ve kidney biopsy.
5 times upper limit of normal can safely undergo a kidney biopsy.The rest of the patients should undergo alternate tests that Licensee OA Publishing London 2013.Creative Commons Attribution Licence (CC-BY) F : Golay V, Roychowdhury A. The percutaneous native kidney biopsy: a nephrologist's perspective.OA Nephrology 2013 May 27;1(1):8.