Potassium in cats and dogs

What it shows

According to the Merck Veterinary Manual, at least 95% of the body’s potassium is inside cells, most of it in skeletal muscle. The kidneys get rid of the excess under the control of the hormone aldosterone. eClinPath stresses that the blood value does not always reflect total body potassium: it is tightly regulated and can look normal despite a large deficit, and shifts between cells and blood (insulin, acid-base changes) move it without any loss or gain.

Serum and plasma give slightly different numbers. During clotting, platelets release potassium, so serum is higher: eClinPath cites differences of up to 0.7 mmol/L in dogs and up to 1.6 mmol/L in cats.

Higher than reference — what it may be a sign of

• Urine cannot leave or kidneys excrete too little: urinary tract obstruction or bladder rupture, acute kidney failure with little or no urine.
• Lack of aldosterone: Addison’s disease — Merck notes hyperkalemia frequently occurs in dogs with it.
• Shift out of cells: tissue damage, insulin deficiency, some types of acidosis.
• Artefacts (pseudohyperkalemia): hemolysis; Akitas and other Japanese or Asian breeds, whose red cells are rich in potassium; a high reticulocyte count in dogs; a very high platelet count; EDTA contamination (IDEXX lists falsely high potassium and low calcium); a sample drawn from a line carrying potassium-rich fluids.

Lower than reference

Low potassium comes from losses in urine — chronic kidney disease in cats, heavy urination, loop diuretics, excess aldosterone — and from the gut through vomiting or diarrhea. It also follows a shift into cells (insulin, alkalosis), poor food intake, potassium-poor diets in cats, large volumes of intravenous fluids and hyperthyroidism. Severe lipemia or very high globulins can lower the result slightly with some analyzers. Low potassium causes muscle weakness and can disturb heart rhythm.

Look at together with

• Sodium and the Na/K ratio — high potassium with low sodium raises the question of Addison’s disease.
• Creatinine and urea — kidney function and urine flow.
• Magnesium — eClinPath notes that low potassium may not correct until magnesium is corrected too.
• Bicarbonate — acid-base balance moves potassium between cells and blood.
• CK — in cats with low-potassium muscle weakness CK may be raised.
• Platelets, reticulocytes and calcium — to spot artefacts.

Units and conversion

Potassium is reported in mmol/L or mEq/L; for potassium the two are the same number. In the app each row keeps the unit printed on the form.

Reference range

The reference range is on your lab’s form. Because serum runs higher than plasma, compare results measured in the same sample type. The Merck Veterinary Manual advises measuring potassium in heparin plasma separated immediately after collection. A high potassium in an animal that looks well is often rechecked on a fresh, carefully handled sample before conclusions are drawn.

Cats and dogs

Sources

1. eClinPath (Cornell University) — Potassium
2. Overview of Disorders of Potassium Metabolism in Animals. Merck Veterinary Manual
3. Feline Hypokalemic Polymyopathy. Merck Veterinary Manual
4. VCA Animal Hospitals — Hypokalemia (Low Potassium Levels) in Cats
5. IDEXX Reference Laboratories — Specimen Collection Guidelines
6. Whitbread TJ. Clinical Biochemistry. Merck Veterinary Manual
7. Cornell Feline Health Center — Feline Lower Urinary Tract Disease