Ultrasound-guided kidney biopsy
Kidney biopsies are important in patients with persistent and refractory protein loss in the urine (proteinuria). The kidneys' main functions are to retain water and to filtrate the blood to remove toxins. The kidneys work like a 2-stage filter. The first stage is the glomerulus, which works to retain big structures like proteins within the bloodstream. Then, there is a finer filter called tubules. The tubules do the fine-tuning. When referring to proteinuria, one assumes that other sources of protein in the urine, such as the presence of a significant amount of blood, inflammation, and infection have been ruled out. In this case, we call it glomerular proteinuria. Cats, specifically, can also have significant amounts of tubular proteinuria.
"Holes" in the glomerulus lead to proteinuria and that proteinuria creates further damage to the tubules. If proteinuria is left untreated, chronic injury to the kidneys can lead to chronic kidney disease.
Proteinuria has typically been treated with high doses of omega 3 fatty acids (oftentimes 50-100 mg/kg per day of EPA as well as medications that cause vasodilation of the efferent arteriole (eg. enalapril, benazepril, telmisartan). This makes it easier for blood to leave the kidney, decreasing glomerular pressure and subsequently proteinuria. A kidney biopsy is recommended in patients that fail to respond to supportive care. Causes of proteinuria include chronic kidney disease, hypertension, infectious diseases, immune-mediated diseases, cancer, and amyloidosis, among others.
Besides kidney damage, proteinuria can lead to hypoalbuminemia and increase the chances for thromboembolism (increased chance of patient throwing clots) due to loss of antithrombin. Severe hypoalbuminemia and subtle increases in creatinine are strong indicators of considering a kidney biopsy prior to significant worsening of kidney function.
Ultrasound-guided kidney biopsy is non-invasive.
When collecting a kidney biopsy, it is important to make sure that there are enough glomeruli in the sample. This is done by evaluating the sample under magnification. It is also very important to submit the sample to a reference laboratory that will evaluate the sample via light microscopy, immunofluorescence, and electron microscopy. This is more expensive than the conventional light microscopy evaluation. However, it is essential in order to diagnose common glomerular diseases.
Focal segmental glomerulosclerosis
Bleeding, worsening azotemia and anesthetic complications are possible. We recommend placing the patient on IV fluids for a few hours prior to and after the procedure. We also recommend monitoring for bleeding post-biopsy.