Protein in urine (dipstick, quantitative, microalbumin) in cats and dogs

What it shows

On a form this topic can appear in three different lines:

• Dipstick protein (PRO) — a pad on the test strip graded negative, trace, 1+ to 4+. It reacts mainly to albumin and much less to other proteins (eClinPath, Merck).
• Quantitative urine protein — protein concentration measured by a chemistry analyser. It is a real number, but it rises and falls with how concentrated the urine is. Divided by urine creatinine, which corrects for concentration, it becomes the UPC — the test vets use to measure protein loss (eClinPath).
• Microalbumin — a sensitive test for small amounts of albumin. Merck describes species-specific tests that detect about 1–30 mg/dL. IDEXX notes that it sees only albumin and is prone to false positives, so a positive result is followed up with a UPC.

Higher than reference — what it may be a sign of

• Blood, inflammation or infection in the urinary tract — they add protein to urine without kidney damage (eClinPath). That is why the sediment is checked first.
• Kidney disease — leakage through the kidney filter (glomeruli) or poor reabsorption by the tubules; the UPC article explains how vets tell them apart.
• Short-lived causes — fever, shock or intense exercise (IDEXX).
• Corticosteroid medicines at immunosuppressive levels can mildly raise the UPC in dogs (eClinPath).
• False positives on the strip — strongly alkaline urine (pH above 8, uncommon in practice), leaving the strip in urine too long, and detergents or disinfectants such as chlorhexidine in the sample (eClinPath).

Lower than reference

Negative is the expected result. A negative strip does not exclude every kind of protein loss: the pad reacts poorly to Bence-Jones proteins (free light chains made by some tumours), which a different test may pick up (eClinPath). For quantitative protein and microalbumin, a low value has no meaning of its own.

Look at together with

• Urine specific gravity — the same grade means more in dilute urine.
• Urine sediment — IDEXX calls a sediment active when it has many white cells or red cells, red or pink colour, or bacteria; protein is then not interpreted until the cause is resolved.
• Urine culture — if the sediment suggests infection.
• UPC — the next step when protein persists with an inactive sediment.
• Urine blood — bleeding adds protein to urine.
• Creatinine and albumin in blood — kidney function and whether heavy protein loss has lowered blood albumin.

Units and conversion

The dipstick result has no unit — it is a grade. Behind each grade lies an approximate concentration that depends on the strip: on the analyser at Cornell’s laboratory, 1+ is about 15 mg/dL, 2+ about 30, 3+ about 100 and 4+ 500 mg/dL or more (eClinPath). A strip is a guide, not an exact number. Quantitative urine protein is reported in g/L or mg/dL: 1 mg/dL equals 0.01 g/L, so 30 mg/dL is 0.3 g/L. Microalbumin is reported in mg/L or mg/dL: 1 mg/dL equals 10 mg/L. In the app each row keeps the unit printed on the form; the chart converts numbers to one unit.

Reference range

The reference range is on your lab’s form; for the dipstick it is usually “negative”. The grade is read against urine specific gravity. According to eClinPath, negative to trace is typical in concentrated urine (above 1.025); in dilute urine (below 1.015) even trace to 1+ is abnormal; more than 2+ (3+ or 4+) in any urine points to significant protein loss. A positive result leads to a look at the sediment and, once blood, inflammation and infection are excluded, to a UPC (IDEXX). Protein loss counts only if it persists on repeat tests.

Cats and dogs

Sources

1. eClinPath (Cornell University) — Urinalysis: chemical constituents
2. Whitbread TJ. Urinalysis. Merck Veterinary Manual
3. IDEXX — Proteinuria: diagnostic update
4. VCA Animal Hospitals — Urinalysis