A kidney biopsy is one of the most accurate methods of diagnosing a range of diseases. But, the procedure is invasive. And, it can be expensive for a hospital to maintain the necessary space and equipment for a percutaneous biopsy.
As a result, clinicians are performing fewer kidney biopsies than they used to. This hesitancy can be dangerous for patients, as treatments for serious conditions are frequently more effective the sooner you start them.
Moreover, kidney biopsy samples are increasingly inadequate. A recent Kidney International report determined the miss rate—the rate at which clinicians took an unusable biopsy sample—increased from 2% to 14% in the past fifteen years.
This guide aims to be a corrective measure. Here, you will learn distinctions among different kidney biopsies and when to order them. Then, read further to discover up-to-date best practices, methodical considerations, and clarity on diagnostic and analysis processes.
Advances in diagnostics and renal care are saving lives and making healing easier. Learn how to get your kidney patients the right treatment, faster.
Kidney Biopsies: Overview
Surgeons first introduced kidney biopsies in the 1950s. Since then, medical specialists have improved biopsy tools and techniques. Today, it’s possible to gather higher-quality samples by less-invasive methods.
What Is a Kidney Biopsy?
A renal biopsy is a three-phase process. The kidney biopsy procedure is an effective tool for diagnosing kidney diseases. Biopsies of donor kidneys inform transplant decisions.
Kidney Sample Extraction
First, a nephrologist takes the sample of kidney tissue. Typical biopsies extract a “core.” The core is a cylindrical sample encompassing several layers of kidney tissue.
Nephrologists extract the core with a core-cutting needle. They take two cores for donor kidney assessment, as a second core increases the assessment’s accuracy.
Core Sample Preparation
Then, technicians prepare the sample for observation. Preparation typically requires sectioning the sample for slides. Each section is 2-3 μm thick. It may also require:
- Fixing
- Staining
- Transport preparation
- Biobanking preparation
Fixing and other preparation processes vary depending on how you want to evaluate the sample. There are also different protocols for shipping samples. And, divergent diagnostic observations benefit from different staining methods.
Evaluation and Interpretation
Finally, nephrologists evaluate the core(s) and interpret the results. Contemporary practitioners use one of five processes to glean information from a biopsy core:
- Immunofluorescence (IF)
- Immunohistochemistry (IHC)
- In-situ hybridization (ISH)
- Electron microscopy (EM)
- Light microscopy (LM)
After evaluation, the practitioner creates a report. The report contextualizes information from the sample. It may include diagnoses or transplant recommendations.
When Should You Order a Kidney Biopsy?
Because a kidney biopsy is invasive, it’s only appropriate to order one when the potential benefits are likely to outweigh the risks. Benefits outweigh risks when the biopsy will likely:
- Enable diagnosis
- Improve diagnostic accuracy
- Determine donor kidney suitability, compatibility for transplant
- Routine check for allograft dysfunction after transplant
Allograft dysfunction can be asymptomatic. The American Society of Nephrology publishes guidelines on when to order a kidney biopsy. Before ordering a biopsy for diagnosis, you must:
- Suspect a patient’s disease will reduce their quality of life, or increase risk of death
- Note that the suspected disease can improve with treatment
- Note that the different diseases potentially afflicting the patient require different treatments
- Inform patient of procedural risks and risks of potential treatments
- Get affirmative patient consent to biopsy
Different types of biopsies bear different risks. The most common risks are bleeding in urine and pain at the biopsy site.
What Can a Biopsy Tell You About a Kidney?
Biopsies can give you information about the tissues and proteins in a kidney. Skilled renal pathologists process information from the sample, then correlate that information with clinical data.
Clinical data includes both general data about kidney diseases and patient-specific information.
Qualitative Information
Pathologists are looking at the qualities of the sample’s discrete parts. They’re examining the hue, density, relative hardness, shape, and texture of the tissue. Specifically, they’re observing:
- Glomeruli
- Tubules
- The interstitium
- The vessels
The pathologist will give brief qualitative descriptions of these components in their report.
Quantitative Information
Pathologists also record quantitative data from the sample. They determine:
- Glomeruli (total number and average density)
- Quantity of glomerular lesions
- Presence and quantity of crescents
- Number of crescents by subtype (cellular, fibrocellular, fibrous)
The best practices for kidney biopsies aim to give pathologists a good sample. The best samples have features that are easy to observe and quantify.
Optimal Kidney Biopsy Size
There is no singular best practice for core size. Larger samples are easier to interpret. And, they result in more accurate diagnoses, particularly regarding disease severity.
But, needles with larger gauges increase the risks of bleeding and hematoma. Most specialists perform biopsies with 14G-18G needles. Editors of the journal Nephrology Dialysis Transplantation recommend biopsy cores with these dimensions:
≥1cm length
≥0.12cm diameter
Larger samples improve diagnostic accuracy. Most pathologists prefer a biopsy with at least 10-15 glomeruli. This ensures the sample is large enough to more accurately represent the kidney as a whole.
Kidney Biopsy Options: Percutaneous vs. Open vs. Transjugular
There are three kidney biopsy methods. Percutaneous biopsies are the most common. Open and transjugular biopsies are typically reserved for special patient populations.
While this guide cannot explore each procedure in-depth, it’s wise to continue your investigation beyond this overview. Consult with experts to determine which operation is best for different patients in your care.
Percutaneous Biopsy
The percutaneous biopsy is the least-invasive kidney-sampling method. Practitioners use ultrasounds or CT devices to guide the movement of the needle.
The American Journal of Roentgenology [Radiology] published a concise write-up defining the imaging-guided percutaneous renal biopsy as it’s practiced today. Nephrologists have permormed percutaneous biopsies long enough that there are established best practices.
Best practices include:
- Mastering biopsy operator techniques
- Weighing the merits of caudocranial needle trajectory (patient ease)
- Calculating optimal needle depth
- Choosing CT-imaging over ultrasound imaging, when possible
Percutaneous biopsies are not appropriate for certain high-risk patients.
Transjugular Kidney Biopsy
Transjugular kidney biopsies are the second-most utilized renal biopsy. The transjugular kidney biopsy is a safer alternative for high-risk patients. Patients who face elevated risk during kidney biopsy include:
- Patients with coagulopathy
- Patients with thrombocytopenia
- Patients with a single functioning kidney
- Patients with small kidneys
- Patients with deranged International Normalized Ratio (INR)
- Patients unable to lie in the prone position
The transjugular kidney biopsy reduces the risk of bleeding and related complications. The method directs all blood from the puncture back into the patient’s veins.
When done correctly, transjugular kidney biopsies are significantly safer than percutaneous biopsies. But, mastering the technique is challenging.
Transjugular biopsies are less common because fewer clinicians can perform them well. Healthcare systems may find a great return if they invest in training nephrologists in this technique.
Open (Laparoscopic) Kidney Biopsy
The open laparoscopic kidney biopsy is not performed as frequently as other modes. It requires multiple surgical incisions. And, it bears a higher risk of bleeding and related complications.
That said, it may only seem riskier statistically. Nephrologists only order open laparoscopic biopsies for patients who cannot undergo percutaneous biopsies.
Typically, these patients can only undergo direct-vision guided biopsies (as opposed to imagine-guided procedures). Patients in this category include:
- Patients with chronic anticoagulation/coagulopathy
- Morbidly obese patients
- Patients who object to blood transfusions on religious grounds
Patients receive open laparoscopy under general anesthesia. Often, surgeons establish direct vision using ports. While these two factors make the procedure riskier, it remains the best option for some patients with contraindications.
Kidney Biopsy Tools
Technicians perform renal biopsies with a needle. Needles can be automated or manual. There are advantages and disadvantages to typical needle sizes.
Automated Biopsy Gun vs. Manual Sheathed Needle
Manual sheathed needles became the standard biopsy tools in 1961. But, many hospitals have replaced manual needles with spring-loaded, automated biopsy guns.
In comparison studies, both biopsy tools take samples effectively. But, automated biopsy guns demonstrate advantages over their manual counterparts:
- Lower incidence of post-biopsy hematoma
- No impact on patients’ hematocrit levels (vs. average -0.9% hematocrit level reduction)
- Reduced bleeding overall
- Lower incidence of severe bleeding
Automatic biopsy needles also have advantages for special patient populations. In pediatric cases, an automatic biopsy gun enabled clinicians to take a viable sample with an 18 gauge needle.
The narrower needle reduces the risk of bleeding and complications, which are elevated in children. And, the automated device reduces the time spent maneuvering the needle during the biopsy. This, too, reduces risk to the patient.
Automated Needle Gauge Size (14 vs. 16 vs. 18)
A needle’s gauge size tells you the diameter of its hole. During a biopsy, you take a sample of the kidney’s tissue through the needle’s hole, filling the needle’s hollow. The typical yield taken with 14 gauge and 16 gauge needles is the same (10-20 glomeruli).
Lower numbered gauges have larger holes. The industrial gauge standard took fractions of the French metric standard unit (since discontinued). Then, industries used the denominator of the fractional measurement of a gauge as its size.
Biopsies require larger needles than those used for IVs. There are three needle gauge sizes for biopsies:
- 14 gauge
- 16 gauge
- 18 gauge
As gauge diameter increases, so does the risk of complications. One comparison study determined that when clinicians perform a biopsy with 14 gauge needles, they see a greater incidence of post-biopsy hematomas.
Among 14G-needle biopsy patients, 41%developed hematomas. In contrast, only 17% of 16G-needle biopsy patients developed hematomas. Moreover, 14G-needles are associated with more frequent blood loss incidents requiring transfusion.
18G-needles reduce risks further. But, in some studies,18 gauge needles yield fewer glomeruli. Typically, 18G-needles are reserved for patients who already bear an elevated risk of complications.
Kidney Biopsy Analysis and Diagnosis
Assessment and diagnosis cannot happen in a vacuum. A kidney biopsy is a clue. Trained pathologists can interpret the information in a biopsy with a range of methods; you’ll read an overview of the most common in this section.
But a single clue is not enough to solve a mystery. It’s important to send contextual information along with the biopsy. The patient’s electronic health records, lab work results, and other relevant information will inform the pathologist’s diagnosis.
Staining
Staining makes it easier to identify distinct elements of your tissue sample under a microscope. Stains and dyes enhance contrast. For instance, staining a cell can clarify the distinction between organelles and the cytoplasm they rest in.
Technicians typically stain kidney biopsies with one of five methods:
- Von-Kossa staining
- Hematoxylin and Eosin (H&E)
- Periodic Acid–Schiff Reaction (PAS)
- Grocott-Gomori’s Methenamine Silver Stain (GMS)
- Picrosirius Red Staining
To learn the specific, step-by-step process of each method, follow the links in the list above.
Different methods advance different diagnostic aims. Picrosirius red staining makes analyzing samples with renal fibrosis easier. H&E staining clarifies glomerular morphology effectively.
If you know what the pathologist is looking for, that must inform your staining choice during sample preparation.
Evaluation Methods
There is no one-size-fits-all method to evaluating renal biopsies. The best methods for diagnosis differ from the best prognosis evaluations.
Moreover, innovators continually advance the art of biopsy analysis. In the future, functional MRI analysis or large-scale 3D tissue cytometry may be the new standard of kidney diagnostics. After all, some of the best practices five years ago are obsolete today.
At the present moment, there are five popular evaluation methods. If you’re in medicine or transplant services, it’s smart to be aware of:
- Immunofluorescence (IF)
- Immunohistochemistry (IHC)
- In-Situ Hybridization (ISH)
- Electron Microscopy (EM)
- Light Microscopy (LM)
Nephrologists use EM in diagnosis more frequently than any other method. Advances in whole-slide digital imaging made EM more affordable than some other methods while retaining its general accuracy.
Per one meta-analysis, EM played an “important or essential” role in 39% of kidney-disease diagnoses. EM is a more effective diagnostic tool than IF or LM.
IHC determines the tissue distribution of antigens. Specialists typically use IHC for cancer diagnoses. One recent comparison study determined that IHC enables immunoglobulin-detection more effectively than IF.
ISH enables analysts to localize DNA and RNA sequences. It also lets specialists determine the degree of gene expression. Nephrologists may use ISH to diagnose renal cell carcinoma or NPHP1 deletion–related nephronophthisis
Remote Biopsy Imaging and Diagnosis for Your Network
At Specialist Direct, we believe every patient deserves premium, data-driven care. We also know that rural communities, hospitals battling rising costs, and transplant organizations face unique challenges.
That’s why we’ve developed a suite of telemedicine solutions. Our digital pathology team can interpret kidney biopsies within an hour, no matter when you need them. Specialist Direct’s automated whole slide imaging microscope and scanner makes sending readable, digital slides easy.
We get healthcare groups accurate results, no matter where you are. Contact us for a free consultation today.