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THE PET HEALTH LIBRARY
By Wendy C. Brooks, DVM, DipABVP
Educational Director, VeterinaryPartner.com

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Zinc Poisoning in Dogs and Cats

Photo by MarVistaVet.com

Red Blood Cell Destruction

Most people have at least a passing familiarity with hemoglobin. Hemoglobin is the iron-containing protein that is responsibly for the red color of blood. It binds the oxygen we breathe in and carries it to our tissues, exchanging oxygen for carbon dioxide and carrying that to our lungs to be exhaled away. Our red blood cells have no nucleus and no DNA, and they do not participate in most normal cellular functions; they are simply bags of hemoglobin being conducted around our blood vessels.

A normal canine red blood cell lives approximately 120 days (60 days for feline red cells) and it dies when it either becomes too stiff to fold itself through tiny capillaries and bursts trying to do so or it simply cannot generate enough energy to keep itself alive.

The spleen is responsible for removing old red blood cells. The spleen possesses many tortuous, winding blood vessels where red blood cells may break if they are not supple enough to pass through. The spleen then collects the hemoglobin. Bilirubin, a pigment made from old hemoglobin, is a by-product of this process. Bilirubin is sent to the liver to be conjugated, a chemical process enabling the bilirubin to be excreted in bile, a digestive emulsifier secreted by the liver. Bilirubin is responsible for the brown color of feces.

What is Hemolysis?

Hemolysis is the destruction of red blood cells. Red blood cells may be destroyed by:

  • immune-mediated pathways (in which the immune system treats red blood cells as foreign cells to be destroyed) 
  • the spleen’s pathways described above 
  • parasites that live in or on on the red blood cell (such as Mycoplasma haemofelis). 
  • toxins such as zinc or copper 
  • infections or tumors.

When too many red blood cells are destroyed, the body’s mechanisms for processing hemoglobin are overwhelmed and bilirubin builds up. The patient may be obviously yellow (jaundiced or icteric) when the mucous membranes are examined. The serum may be yellow when checked in a blood sample. If the blood cells are being destroyed in the blood stream rather than in the spleen, the urine will turn red or rust colored. Hemoglobin is toxic to the kidneys and kidney failure is a strong possibility.

Zinc

Photo Credit: Jennie Marvelle, DVM, Boothbay Animal Hospital Boothbay, ME

In 1983, the U.S. government began minting pennies made of zinc wafers coated in copper rather than out of pure copper. As it is not uncommon for young animals to swallow pennies, zinc toxicity became recognized.

Other zinc sources include nuts, bolts, and zinc oxide-based skin creams, such as diaper rash cream and sun screen. You can see a penny or other radio dense object of about the right size on a radiograph or there may be a known history of penny eating. It is important to rule out immune-mediated hemolysis as this is a common condition requiring specific treatment.

Clinical Signs

The clinical signs of zinc toxicosis include:

  • vomiting
  • diarrhea
  • red urine
  • icterus (yellow mucous membranes)
  • liver failure
  • kidney failure
  • anemia

Vomiting and diarrhea generally precede the destruction of red blood cells. How zinc produces hemolysis is not known. With zinc-containing ointments, usually only stomach upset is seen after the ointment is licked but if the ointment is applied and licked regularly, full zinc toxicity can develop.

Treatment

If an object possibly made of zinc is seen on an X-ray, it should be removed promptly. This might involve surgery, endoscopy, or possibly inducing vomiting if the object does not have sharp edges. Support then becomes crucial. Fluid therapy is important to keep adequate circulation to the kidneys and help prevent failure. Transfusion may be necessary to combat anemia and anti-nausea therapy is warranted. Zinc is corrosive to the stomach so medication to protect the stomach will be needed. Antacids are helpful in reducing absorption of zinc, which is enhanced by stomach acid. Research is looking at methods for binding excess zinc in the circulation similar to the way lead poisoning is treated.

Once the zinc source is removed, most pets are able to recover within 48-72 hours with supportive care, but of course this depends on the severity of the poisoning.

 

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