Glomerulonephritis in cats: causes, symptoms and prevention

• older cats;
• cats with chronic infections;
• cats with autoimmune diseases;
• pets with prolonged inflammation.

Ageing increases the likelihood of many kidney diseases, but glomerular disease is not limited to older cats. Studies based on kidney tissue samples have also identified it in young adults. Little is known about independent risk factors in cats, and findings in selected research patients do not show how common the disease is across the whole cat population.

To confirm the diagnosis, investigations include:

• a urine sample to check protein, casts and specific gravity;
• blood biochemistry, including creatinine, urea and protein levels;
• blood pressure measurement;
• kidney ultrasound;
• a kidney biopsy, the gold standard for confirming the diagnosis;
• tests for viral and bacterial infections.

Proteinuria first needs to be shown to persist and its source located. Blood, pus cells or bacteria in urine may explain a protein finding without primary glomerular disease. Urinary cells and sediment are therefore examined and results compared with blood biochemistry. A single dipstick result does not confirm the diagnosis.

The amount of protein leakage is assessed using the urine protein-to-creatinine ratio, or UPC. Repeated measurements show the direction of change, but even a high value cannot, on its own, distinguish immune-mediated inflammation from other glomerular diseases. Kidney function, albumin and blood pressure are assessed at the same time. Blood pressure is measured in calm surroundings because anxiety can affect the reading.

Ultrasound helps assess kidney structure and other possible diseases, but cannot reliably show immune-complex deposits. In addition to ordinary microscopy, a tissue sample often needs electron microscopy and immunofluorescence to look for deposits of immune-system proteins. Sample handling and shipping are planned accordingly.

A biopsy is not taken automatically from every cat. Its benefits are weighed particularly in severe or progressive disease, or disease responding poorly to standard treatment for protein loss. The investigation must be able to affect a treatment decision. Untreated high blood pressure and clotting disorders increase bleeding risk and may prevent sampling.

Glomerulonephritis can be:

• acute, starting suddenly with rapid deterioration;
• chronic, developing slowly and potentially remaining unnoticed for a long time.

How quickly symptoms start does not, on its own, determine whether damage is reversible. A chronic disease can worsen suddenly because of dehydration or another illness, for example. Equally, a cat appearing well for a long time does not guarantee that protein leakage is controlled. Monitoring results are compared with previous findings.