Renal biopsy (also kidney biopsy) is a medical procedure in which a small piece of kidney is removed from the body for examination, usually under a microscope. Microscopic examination of the tissue can provide information needed to diagnose, monitor or treat problems of the kidney. A renal biopsy can be targeted to a particular lesion, for example a tumour arising from the kidney (targeted renal biopsy). More commonly, however, the biopsy is non-targeted as medical conditions affecting the kidney typically involve all kidney tissue indiscriminately. In the latter situation, any sufficiently sized piece of kidney tissue can be used. A native renal biopsy is one in which the patient's own kidneys are biopsied. In a transplant renal biopsy, the kidney of another person that has been transplanted into the patient is biopsied. Transplant kidney biopsy can be performed when nothing is apparently wrong with the transplant kidney for the purposes of surveillance for hidden disease (protocol transplant biopsy). This is typically done at 0, 3 and 12 months post-transplant according to a transplant unit protocol. Biopsy of the transplanted kidney taken during the transplant operation is termed implantation transplant biopsy or post-perfusion transplant biopsy depending on the timing of the biopsy with respect to key stages of the operation. When the transplanted kidney is not working properly, biopsy may be undertaken to identify the cause of dysfunction. This is referred to as an indication transplant biopsy, because something has prompted the performance of the biopsy. Renal biopsy may be performed with the aid of "real-time" medical imaging to guide the positioning of biopsy equipment (imaging-guided renal biopsy). Alternatively, a biopsy may be performed without imaging-guidance using indirect assessments of position such as "needle-swing" to confirm appropriate placement of biopsy equipment (blind renal biopsy).
History Before 1951, the only way of obtaining kidney tissue from a live person was through an open operation. In 1951, Danish physicians Poul Iversen and Claus Brun described a method involving needle biopsy which has become the new standard. Recent widespread availability of real-time imaging guidance using ultrasound or CT scanning having improved perceived safety of the procedure.
Indications Kidney biopsy is performed on selected patients with kidney disease. It is most commonly used when less invasive tests are insufficient. The decision on whether or not to proceed to a kidney biopsy is usually made by a nephrologist. The following are examples of the most common reasons for native kidney biopsy:
Haematuria (or blood in the urine) can occur with a number of conditions that affect the kidneys and urinary tract. While renal biopsy is not indicated in all cases of haematuria, it may be performed in those with glomerular haematuria (blood that is thought to come from damage to the glomerulus) or when combined with features of progressive renal disease (e.g. increasing proteinuria, elevated blood pressure and kidney failure). One example is the nephritic syndrome. Proteinuria (or protein in the urine) occurs in many renal conditions. Renal biopsy is usually reserved for patients with high or increasing levels of proteinuria, or for patients who have proteinuria along with other signs of renal dysfunction. One example is the nephrotic syndrome. Kidney failure (or impaired kidney function due to kidney injury) can occur abruptly (acute kidney failure) or progress over a period of time (chronic kidney disease). The cause of acute kidney failure can usually be determined without kidney biopsy. Biopsy is performed in those instances where the cause is uncertain. Targeted kidney biopsy can be used to obtain tissue from a tumour arising from or adjacent the kidney. Transplant kidney biopsy is performed in the following circumstances:
For surveillance of hidden disease involving the transplant kidney, so-called protocol renal biopsy undertaken at fixed intervals post-transplantation. When the transplant kidney is not working as well as expected, or when there is a deterioration in function. In these instances, biopsy is performed to exclude rejection, BK nephropathy, drug-toxicity or recurrence of the disease that caused kidney failure in the first place.
Contraindications The safety of renal biopsy is affected by the following conditions:
Absolute bleeding diathesis uncontrolled severe high blood pressure uncooperative patient presence of a solitary native kidney
Relative azotemia or uraemia certain anatomical abnormalities of the kidney skin infection at the biopsy site medications that interfere with clotting (e.g. warfarin or heparin) pregnancy urinary tract infection obesity
Procedure
Before biopsy Like most invasive medical procedures, a renal biopsy is not without risk (see Complications). A nephrologist will have to satisfy themselves that a renal biopsy is of appropriate benefit to justify the risks of the procedure before proceeding. This will include careful consideration of patient characteristics and other clinical information obtained from history, examination and other less-invasive investigations. Blood testing may be done before the biopsy to ensure that there is no evidence of infection or a blood clotting abnormality. Further, an ultrasound or other imaging study of the kidney may be performed before biopsy to exclude structural problems of the kidney, which may theoretically increase the risk of the procedure. These include hydronephrosis, pre-existing arteriovenous fistula in the kidney, cystic kidney disease and small, shrunken kidneys. To decrease the risk of bleeding, patients are usually advised to avoid medicines that impair clotting for one to two weeks before the biopsy. These medications include aspirin, clopidogrel, heparin and warfarin. Desmopressin may be administered intravenously in the hope of reversing the clotting disturbance that accompanies kidney failure (uraemic coagulopathy). Strict control of blood pressure is also sought to reduce bleeding risk. Prior to the procedure, informed consent is usually taken. Arrangements will also be made to ensure that appropriate post-biopsy care and supervision is in place. Fasting is usually not required. However, this will depend on centre preference.
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