A single urine protein to creatinine ratio of 0.6 in a cat does not prove glomerulonephritis. The ratio swings with hydration, stress, and how long the sample sat in the fridge, so the diagnosis needs 2 abnormal samples at least 7 days apart, a quiet urine sediment, and a reason for the protein to be leaking. Once confirmed, care is built on 3 rechecks: the ratio itself, kidney values, and blood pressure. Get those on a schedule and most cats are managed for years rather than weeks.
What the glomerulus is supposed to hold back
Each kidney holds roughly 200,000 nephrons, and every nephron starts with a filter that keeps albumin in the blood while letting water and small waste through. When immune complexes, amyloid, or chronic infection damage that filter, albumin leaks into the urine. The tubules try to reabsorb it and, over months, scar. That is why protein in the urine is a kidney problem even when creatinine is still 1.6 mg/dL and the cat looks fine. In cats the common drivers are feline infectious peritonitis, feline leukemia virus, feline immunodeficiency virus, chronic dental or skin infection, and tumors; a minority have familial amyloidosis, seen more often in Abyssinian and Siamese lines.
The UPC numbers and what each band means
The ratio compares protein and creatinine in the same urine sample, which cancels out how concentrated the urine happens to be. Under 0.2 is normal. From 0.2 to 0.4 is the grey band: repeat in 2 to 4 weeks before calling it anything, because a cat with a urinary tract infection, a fever, or 24 hours of not eating can sit at 0.3 and then drop to 0.1. Above 0.4 is proteinuria and needs a workup. Above 2.0 usually means glomerular disease rather than tubular leakage, and above 3.5 the cat is losing enough albumin to be at risk of clotting problems and body cavity fluid. One caveat: blood in the urine inflates the ratio, so check the sediment first and treat cystitis before you chase the number.
The 3 rechecks, in order
First recheck is the ratio, repeated at 7 to 14 days on a first-morning sample collected at home if the cat tolerates it, with a sediment exam each time. Three samples over 4 weeks is the practical standard, and the trend matters more than any single value. Second is kidney function: creatinine and symmetric dimethylarginine together, because creatinine stays normal until roughly two-thirds of nephron mass is gone, while SDMA rises earlier. Third is systolic blood pressure, measured before any other handling, since 1 in 3 proteinuric cats is hypertensive and pressure over 160 mmHg damages the retina and the filter at the same time. Albumin belongs in the same visit: a value under 1.5 g/dL is the point where fluid leaks into the abdomen and clots become a real risk.
Numbers to track, and how often
| Measure | Target or trigger | Recheck interval |
|---|---|---|
| UPC ratio | Under 0.2 normal; over 0.4 abnormal; aim for half of baseline | 14 days, then every 8 to 12 weeks |
| Creatinine | Under 1.6 mg/dL is stage 1; 1.6 to 2.8 is stage 2 | 30 days, then every 12 weeks |
| SDMA | Under 14 micrograms/dL is normal | 30 days, then every 12 weeks |
| Systolic blood pressure | Under 160 mmHg; treat at 160 or above | 14 days, then every 12 weeks |
| Albumin | 2.2 to 4.0 g/dL; under 1.5 means fluid risk | 30 days |
| Urine culture | No growth; any growth gets treated and rechecked | At every ratio sample |
Two rules keep the table honest. Measure blood pressure before the cat is restrained for blood draws, because 10 minutes of restraint can add 20 mmHg. And always run the culture, since a low-grade infection can hold the ratio above 0.4 for months no matter what else is done.
Where protein loss shows up outside the kidney
Cats hide the early stage well. The first owner-visible sign is often water: fluid under the skin of the limbs, a belly that looks full at 6 months after a normal weight, or labored breathing from fluid around the lungs. Weight gain of 300 g in 2 weeks with no change in appetite is more likely fluid than fat. Hypertension shows itself as sudden blindness from a detached retina, dilated pupils that do not react, or a seizure. A cat drinking more and urinating more should also be checked for a blocked bladder, which is a same-day emergency — the comparison is in urinary blockage signs.
What treatment is actually aiming at
The goal is not a normal ratio on paper. It is a ratio cut by half, stable creatinine, pressure under 160 mmHg, and albumin above 2.0 g/dL, held for 6 months or more. Most veterinary plans combine a kidney-support diet with restricted phosphorus, a prescription that lowers pressure inside the glomerulus, and treatment of whatever started the damage — dental infection, retrovirus management, or a tumor workup. Blood thinners are added when albumin sits under 1.5 g/dL. Feeding a renal diet early is easier than switching at stage 3, when appetite is already poor.
Five steps to start this week
- Collect a first-morning urine sample in clean litter beads, refrigerate it, and deliver within 6 hours.
- Ask for UPC, sediment, and culture on the same sample, not three separate visits.
- Book the blood pressure check before any blood draw, on the same day as the second ratio.
- Repeat the full panel at 14 days, then move to every 12 weeks once two ratios agree.
- Keep a weekly weight log and a daily water intake estimate, and bring both to each recheck.
Cost is the reason many owners stretch the schedule. A ratio, sediment, culture, and pressure check together cost far less than one emergency visit for fluid in the chest, which is where untreated cases end up — typical ranges are on the cost page. Skipping the 14-day repeat is the single most common way a treatable case is missed.
Terms mentioned in this article
Frequently asked
Does a UPC of 0.5 always mean glomerulonephritis?
No. A ratio between 0.2 and 0.4 is the grey band, and even 0.5 can come from cystitis, fever, or a cat that has not eaten for 24 hours. Diagnosis needs 2 samples above 0.4 taken at least 7 days apart, a sediment free of blood and bacteria, and a negative culture. A cat with all of that plus a rising SDMA is treated as glomerular disease.
How often should a proteinuric cat be rechecked?
Ratio at 7 to 14 days for the confirmation pair, then every 8 to 12 weeks. Creatinine and SDMA at 30 days, then every 12 weeks. Blood pressure at 14 days, then every 12 weeks, and always before blood draws. Albumin and urine culture travel with the ratio, since low albumin under 1.5 g/dL changes the plan immediately.
Can glomerulonephritis in cats be cured?
Rarely cured, often controlled. When the trigger is a treatable infection, the ratio can fall below 0.4 within 8 to 12 weeks. With amyloidosis or an inherited filter defect, the aim is half of baseline plus stable creatinine. Cats that hold a ratio under 1.0, pressure under 160 mmHg, and albumin above 2.0 g/dL often live 2 to 4 years after diagnosis.