Copper, zinc and selenium in cats and dogs

What it shows

Copper, zinc and selenium are trace elements — the body needs them in very small amounts. They are not part of a routine panel; serum goes to a specialised laboratory.

A blood level does not always show body stores. Serum zinc is a fairly insensitive measure of zinc status. A mild copper shortage can exist while serum copper looks adequate, and copper that builds up in a diseased liver is measured in liver tissue. Serum selenium reflects selenium status well, and whole-blood selenium appears to be even better.

Collection matters. Ordinary rubber tube stoppers contain zinc and can falsely raise the result, so labs ask for tubes certified for trace-element testing (for example, royal-blue-top tubes), and serum is ideally separated from the clot within four hours.

Higher than reference — what it may be a sign of

• Zinc poisoning — after swallowing zinc-containing metal: US pennies minted since 1982 (97.5% zinc), galvanised nails, nuts and bolts, hardware, car parts. Zinc destroys red blood cells inside the vessels: anaemia, jaundice, red-brown urine; spherocytes and Heinz bodies on the blood smear. Zinc oxide ointment or lozenges are a low-risk exposure.
• Contamination of the sample — a rubber stopper or a tube not meant for trace elements can make zinc look high.
• Copper — copper-associated hepatitis in dogs is copper building up in the liver. Its diagnosis rests on a liver biopsy with copper measured in the tissue; serum copper on a blood test is a different measurement and does not replace it.

Lower than reference

Copper deficiency is rare in dogs and cats, except in animals fed almost entirely milk or vegetables; it can cause anaemia with small, pale red cells. Zinc deficiency can cause vomiting, eye surface inflammation, loss of coat colour, slow growth and weight loss; some Siberian Huskies and Alaskan Malamutes have an inherited defect in absorbing zinc from the gut, which shows as a skin condition (zinc-responsive dermatosis). A low serum zinc fits a shortage, but because the test is insensitive a value inside the range does not rule one out. For selenium in dogs and cats the sources give no separate clinical picture.

Look at together with

• Complete blood count, reticulocytes and red cell morphology — zinc causes a regenerative haemolytic anaemia with spherocytes and Heinz bodies.
• Lead — the other metal poisoning with anaemia; with lead the anaemia is usually non-regenerative, although nucleated red cells may be seen on the smear, while zinc gives a regenerative one.
• ALT and other liver tests — signal liver injury when copper hepatitis is suspected; the copper itself is then measured in a liver biopsy.

Units and conversion

Copper and zinc are reported in µmol/L or µg/dL. For copper 1 µg/dL equals 0.1574 µmol/L (100 µg/dL ≈ 15.7 µmol/L); for zinc 1 µg/dL equals 0.153 µmol/L (100 µg/dL ≈ 15.3 µmol/L). Selenium is reported in µg/L or µmol/L: 1 µmol/L equals 78.97 µg/L. Liver copper is reported per gram of dry liver tissue — that is a different measurement and cannot be compared with serum. In the app each row keeps the unit printed on the form; the chart converts to one unit so forms from different labs line up.

Reference range

The reference range is on your lab’s form. It depends on the laboratory, the species and the tube. A high zinc from a tube that was not certified for trace elements may be contamination, so the vet will check how the sample was taken. Liver copper thresholds, given in micrograms per gram of dry tissue (for example, above 1,000 µg/g in one toxicology reference), apply to biopsy tissue and are not a range for blood.

Cats and dogs

Sources

1. Carlino M. Zinc Toxicosis in Animals. Merck Veterinary Manual, professional version, full review May 2026.
2. Fritz S. Copper Toxicosis in Animals. Merck Veterinary Manual, professional version, full review April 2026.
3. Center SA. Canine Chronic Hepatitis. Merck Veterinary Manual, professional version, last updated September 2024.
4. Sanderson SL. Nutritional Requirements of Small Animals. Merck Veterinary Manual, professional version, full review November 2023.
5. Michigan State University Veterinary Diagnostic Laboratory. Mineral Diagnostics.
6. Michigan State University Veterinary Diagnostic Laboratory. Mineral and Vitamin Testing — Sample Collection and Handling.
7. Bostrum B, Cook AK. Canine copper-associated hepatopathies: diagnosis. dvm360, August 2008.