Urine pH in cats and dogs

What it shows

pH is a scale from acidic to alkaline: 7 is neutral, lower numbers are acidic, higher ones alkaline. The dipstick pad changes colour across roughly pH 5 to 9 (eClinPath). Dogs and cats normally have acidic urine (Merck), except for a while after a meal, when urine turns more alkaline — the post-meal “alkaline tide” (eClinPath). VCA describes dog and cat urine as ranging from mildly acidic to mildly alkaline, and notes that diet can shift it.

The kidneys use urine to get rid of excess acid or base, but a single urine pH does not reflect the acid–base balance of the whole body; for that a vet needs a blood gas test (eClinPath).

Higher than reference — what it may be a sign of

• A recent meal — the post-meal alkaline tide.
• Urinary tract infection with bacteria that produce urease, an enzyme that turns urea into ammonia. eClinPath advises that persistently alkaline urine in a dog or cat is a reason to test for infection.
• An old sample — urine left standing loses carbon dioxide and its pH rises (eClinPath).
• Kidney tubule disorders such as distal renal tubular acidosis, and systemic acid–base disorders (eClinPath).
• Diet — food can shift urine pH (VCA).

Alkaline urine matters for the rest of the test: above pH 8, red and white cells and casts in the sediment tend to break down (eClinPath), and struvite crystals form in alkaline urine (Merck, eClinPath).

Lower than reference

Acidic urine is usual for cats and dogs, so a low pH on its own is rarely a finding. Systemic acid–base disorders can shift urine pH in either direction (eClinPath). Among crystals, Merck notes that cystine forms in acidic urine. VCA adds that values outside the usual range are more likely linked to infection or metabolic disease.

Look at together with

• Urine sediment — crystals, cells and bacteria are interpreted together with pH.
• Urine culture — if urine stays alkaline, to look for urease-producing bacteria.
• Urine specific gravity — the usual partner for reading every other line of the urinalysis.
• Urine protein — eClinPath lists strongly alkaline urine (pH above 8) as a possible, though uncommon, cause of a false-positive dipstick protein.
• Urine blood — in alkaline urine red cells can break down, so the dipstick may be positive with few cells visible.
• Bicarbonate in blood and blood gases — the actual acid–base status.

Units and conversion

pH has no unit; the number is read as it is and needs no conversion. Strips are not very precise: Merck puts the accuracy of the pH pad at about ±0.5 units and notes that portable pH meters are more accurate. eClinPath reports that observers agree least on pH of all dipstick pads — a true 7.5 can be read anywhere from 7 to 8 — and its laboratory analyser reports pH in whole steps from 5.0 to 9.0. So a half-unit difference between two forms usually means nothing.

Reference range

The reference range is on your lab’s form. Because pH depends on the last meal, the time of day and how fresh the sample is, a single value outside the range is weak evidence. It helps to tell the vet when the animal last ate and how long the urine stood before testing. Merck advises examining urine within 30 minutes or keeping it refrigerated for up to 24 hours; refrigeration does not change pH, although crystals may form in a chilled sample.

Cats and dogs

Sources

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