UPC (urine protein : creatinine ratio) in cats and dogs

What it shows

The lab measures protein and creatinine in the same portion of urine and divides one by the other. Creatinine leaves the body at a fairly steady rate, so it works as a yardstick: the ratio corrects for how concentrated or dilute the urine is, and a spot sample gives about the same answer as a 24-hour collection.

A dipstick also shows protein, but only roughly: it gives false positives and false negatives and cannot say how much protein there is. UPC is the number vets use to confirm and measure protein loss. It matters twice: it helps find kidney disease, and in animals that already have chronic kidney disease (CKD) the amount of protein loss carries weight for the outlook, which is why IRIS substages CKD by UPC.

Higher than reference — what it may be a sign of

• Protein from the lower urinary tract (postrenal): bladder infection, stones, bleeding or inflammation, prostate disease in males, vaginitis in females, tumours. Blood and inflammatory cells add plasma protein to urine — this is not kidney damage, and it is why UPC is measured only when the urine sediment is inactive: no blood, white cells or bacteria.
• Leaky kidney filter (glomerular): glomerulonephritis, amyloidosis. Values of 2 and above fit glomerular protein loss; in amyloidosis UPC often goes above 10.
• Kidney tubules (tubular): the tubules fail to take back the small amount of filtered protein; this loss is usually milder.
• Chronic kidney disease of any cause: according to the ACVIM consensus, persistent protein loss of kidney origin usually indicates CKD.
• Overload (prerenal): small proteins flood the filter — hemoglobin, myoglobin, some tumour proteins.
• Short-lived: fever or heavy exercise can raise protein loss for a while.

Lower than reference

A low UPC means the kidneys are holding on to protein. No disease is defined by a low UPC. Small differences between two samples can be noise — results vary from day to day, and in cats the measurement itself can vary between runs by up to 16–18%. That is enough to move an animal across an IRIS substage line, so a series of tests is best done at the same lab.

Look at together with

• Full urinalysis with sediment — done first. Blood, white cells or bacteria in the sediment make the UPC unreliable; the test is repeated after that cause is resolved.
• Urine specific gravity — trace protein on a dipstick matters more in dilute urine than in concentrated urine.
• Urine culture — rules out infection as the source of protein.
• Creatinine and SDMA in blood — a high UPC with normal blood kidney values does not rule out kidney disease.
• Blood pressure — IRIS substages CKD by both protein loss and blood pressure.
• Albumin in blood — heavy glomerular protein loss can lower it; tubular loss usually does not.

Units and conversion

UPC is a ratio and has no unit: protein and creatinine are measured in the same units and divided, so the units cancel out. Forms may print it as UPC, UPCR, UP/C or “protein/creatinine”. The number reads the same across labs without conversion, but methods differ, so serial measurements are best compared within one laboratory.

Reference range and IRIS substages

The reference range is on your lab’s form, usually as a single upper limit. Protein loss is judged by persistence: IRIS suggests confirming it on two or more samples taken at least two weeks apart, and only after protein from the lower urinary tract has been excluded. One raised result is a reason to repeat the test, not a diagnosis.

When an animal has CKD, IRIS adds a substage by UPC. The cut-offs below are substaging thresholds, not a reference range; the IRIS guidelines remain the primary source.

Source: iris-kidney.com

Cats and dogs

Sources

1. eClinPath (Cornell University) — Urinalysis: chemical constituents (protein, UPC)
2. Van Vertloo L. Renal Dysfunction in Dogs and Cats. Merck Veterinary Manual
3. International Renal Interest Society — IRIS Staging System
4. Lees GE, Brown SA, et al. Assessment and Management of Proteinuria in Dogs and Cats: ACVIM Forum Consensus Statement (IVIS)
5. VCA Animal Hospitals — Urine Protein/Creatinine Ratio