In veterinary medicine, renal biopsy is indicated in patients in which a histologic diagnosis is likely to influence the therapeutic management of the patient or provide significant prognostic information. Therefore, primary indications for kidney biopsy are substantial, unresponsive, or progressive proteinuria and unexplained acute or rapidly progressive kidney injury.^11,12 It is important to realize that these indications are not absolute and that in some cases, clinical and laboratory data may suggest a predictable histologic pattern and therefore kidney biopsy may not be required. Common indications and contraindications for renal biopsy are listed in Box 20-1.

Box 20-1 Indications and Contraindication for Renal Biopsy

In patients with chronic kidney disease (CKD), particularly those in stage 4, it is unlikely that renal biopsy will alter the diagnosis, prognosis, or therapy of the patient.¹³ Although comparative data are not available in veterinary medicine, in human medicine, patients with end-stage renal disease are more likely to have clinically significant complications associated with renal biopsy.¹⁴

In patients with severe acute kidney injury (AKI) or those with AKI not responding as expected to medical management, kidney biopsy may be helpful in determining the underlying etiology and thus in directing specific therapy. More commonly, kidney biopsies are obtained in cases of AKI for prognostic purposes. The overall appearance of the tissue; the integrity of the basement membrane; and the degree of regeneration, if present, may all help the clinician determine if the patient is able to recover from the injury. This information is very important to owners who are faced with continuing intensive and expensive therapies, such as hemodialysis, when supporting patients with AKI.

In veterinary medicine, renal biopsies are most commonly obtained percutaneously under ultrasound guidance. Possible reasons why a clinician might choose a laparoscopic approach over other percutaneous methods include failed ultrasound-guided biopsy (including procurement of samples that contain mainly medullary tissue), lack of ultrasound skills, unavailability of ultrasound, and severe obesity or patients with other anatomic anomalies that would make a percutaneous approach difficult or dangerous. Other potential reasons to consider laparoscopy over ultrasound-guided biopsy include coagulopathy (in which case absolute precision can be achieved with laparoscopy and hemostasis can be achieved under direct vision in a controlled fashion) and when other organs need to be sampled at the same time (in particular the liver, in which case needle biopsies are often inadequate for accurate interpretation). In one study in dogs, laparoscopy was shown to be superior to ultrasound-guided biopsy in terms of the number of glomeruli obtained and resulted in fewer complications.⁷ Despite those findings, there is strong institutional bias in the relative success of ultrasound-guided biopsy, usually related to the skills of the ultrasonographer. This is demonstrated by the results of another study in which renal biopsies obtained at other institutions had no difference in quality when comparing ultrasound-guided and laparoscopy-guided biopsies.¹⁰ In another study, 96% of samples obtained from 25 dogs undergoing laparoscopic renal biopsy were classified as excellent, with only minor complications.⁸

Before biopsy, the patient must be assessed thoroughly to identify factors that could increase the risk of complications of renal biopsy. One of the most important complications is postbiopsy hemorrhage, which can be life threatening in some cases. However, the best preprocedure predictor of renal hemorrhage is unclear. In one study of dogs and cats undergoing ultrasound-guided percutaneous renal and hepatic biopsy, patients with thrombocytopenia were at increased risk for major complications compared with patients with normal platelet numbers.¹⁵ In this study, 8.9% (15 of 168) of patients undergoing renal biopsy had major complications. This suggests that delaying the biopsy until the platelet numbers improve might be warranted, but often this is not clinically feasible. The clinician must therefore weigh the benefits of the information gained from the biopsy with the risk of major bleeding complications. Because coagulation status should be assessed, the minimum data base should include prothrombin time, activated partial thromboplastin time, and a platelet count. Other methods of coagulation assessment may be better predictors of hemorrhage, including assessing proteins induced by vitamin K antagonism (PIVKA) and thrombelastography. Although these methods may have advantages in other clinical situations (e.g., patients with hepatic disease, hypercoagulable patients, and other critically ill patients), they have not been described in patients before renal biopsy. If it is deemed necessary to obtain a biopsy in a patient with thrombocytopenia or a coagulopathy, the clinician should use the smallest needle and fewest numbers of samples necessary to obtain a diagnostic sample. Higher numbers of biopsies increases the risk of a drop in hematocrit, especially after the second sample.¹⁵ The clinician should also be prepared to monitor patients with coagulopathies or thrombocytopenia closely and have compatible blood products available if needed.

Another risk factor for hemorrhage is systemic hypertension, a common finding in patients with renal disease.¹⁶ Studies quantifying the risk of systemic arterial hypertension in patients undergoing renal biopsy are lacking in dogs and cats. However, it seems prudent to attempt to normalize arterial pressure before renal biopsy.

Patients undergoing renal biopsy must be placed under general anesthesia, and therefore every effort should be made to normalize any metabolic or cardiovascular abnormalities that may be present. The patient’s hydration status must be carefully assessed because patients with renal disease are commonly over- or underhydrated. In patients that are underhydrated, intravenous fluid support should be administered before general anesthesia, especially if they are hypotensive. In patients that are overhydrated, fluid therapy should be more judicious or discontinued, and if the patient is oliguric or anuric, stabilization with hemodialysis should be considered.

Before undergoing laparoscopy, the patient should have an ultrasound examination to evaluate the internal architecture of the kidney. Relative contraindications to laparoscopy-guided needle biopsy include renal cysts, ureteral obstruction, and hydronephrosis. These can be readily detected via ultrasonography. In addition, ultrasonography can detect focal renal lesions (e.g., masses, infiltrative areas) to allow selection of the proper kidney and region to be biopsied.