Bilirubin and urobilinogen in urine in cats and dogs

What it shows

Bilirubin is a yellow pigment that forms when old red blood cells are broken down. The liver binds it to another molecule (this is called conjugated bilirubin) and sends it out with bile. Only the conjugated form passes from blood into urine, and the dipstick pad reacts to it; unconjugated bilirubin is not detected by the pad.

Urobilinogen is a second line on many strips. Bacteria in the intestine make it from the bilirubin that arrives with bile; most of it leaves with the faeces, a little returns to the liver and a small amount goes into urine. In animals the link between the urobilinogen pad and liver disease is poor, so vets put little weight on it.

Higher than reference — what it may be a sign of

• Problems with bile flow (cholestasis) — liver or bile duct disease. This is the main cause of bilirubin in urine; in cats a positive result points this way.
• Breakdown of red blood cells inside the blood vessels — can raise urine bilirubin, but this is very rare.
• Concentrated urine in a healthy dog — a small amount can be normal; see the dog section below.
• Urobilinogen above the usual level — in animals the link with liver disease is poor.
• False positive bilirubin — uncommon; medicines that colour urine red can disturb the reading.

Lower than reference

Negative is the expected bilirubin result in cats and a common one in dogs. A negative pad does not rule everything out: light breaks down conjugated bilirubin, bilirubin changes in urine that has stood too long, and a lot of vitamin C in urine can mask it. A fresh sample kept away from light gives the most reliable answer.

For urobilinogen a negative result means little: the strip cannot show true absence, and many healthy animals have no detectable urobilinogen because it is unstable while urine sits in the bladder.

Look at together with

• Total bilirubin in blood — a positive urine result in a cat is followed by a look at blood bilirubin.
• Urine specific gravity — in dogs a trace means more in dilute urine than in very concentrated urine.
• Liver enzymes ALP, GGT and ALT, and bile acids — liver function and bile flow.
• Hematocrit — anemia together with bilirubin in urine raises the question of red cell breakdown.
• Bilirubin crystals in the sediment — appear together with bilirubinuria; a few may be seen in healthy dogs, but in cats they are always abnormal.

Units and conversion

Bilirubin on the strip has no unit: it is a grade — negative, 1+, 2+ or 3+, and some forms also write “trace”. The pad starts to react at roughly 0.2–0.4 mg/dL of conjugated bilirubin, but the grade is a rough guide, not an exact amount. Urobilinogen is printed either as a word (“normal”) or as a number in Ehrlich units (EU/dL) or mg/dL. In the app each result keeps the wording or unit printed on the form.

Reference range

The reference range is on your lab’s form; for bilirubin it is usually “negative”. In dogs the expected result can be negative to 1+, with trace and 1+ found in more concentrated urine; rare 2+ results have been reported in very concentrated urine (specific gravity above 1.040). In cats any bilirubin in urine is significant. For urobilinogen, “normal” or up to about 1 on the strip is the usual finding.

Cats and dogs

Sources

1. eClinPath (Cornell University) — Urinalysis: chemical constituents
2. Whitbread TJ. Urinalysis. Merck Veterinary Manual
3. Merck Veterinary Manual — Miscellaneous serum biochemical measures in hepatic disease in small animals
4. IDEXX — Complete urinalysis panel: interpretation guide
5. Rizzi TE. Urinalysis in companion animals, part 2: evaluation of urine chemistry & sediment. Today’s Veterinary Practice, 2014