Is zinc toxicosis on your radar? Overexposure to this essential mineral can result in a variety of clinical signs and laboratory findings including hallmarks such as hemolytic anemia, bilirubinemia, and pigmenturia. Thus, zinc toxicosis can be misdiagnosed as immune-mediated hemolytic anemia (IMHA), revealing the necessity for imaging in all suspected IMHA cases. Prompt recognition of possible zinc exposure and treatment will provide the best outcome for these patients.
ZINC AS A NECESSARY TRACE ELEMENT
Zinc is an essential trace element with many important functions. More than 200 metalloenzymes require zinc for normal carbohydrate, protein, lipid, and DNA metabolism. Some of these enzymes include carbonic anhydrase, alkaline phosphatase, and urea cycle enzymes.1-3 These metalloenzymes are involved in gene expression, cell membrane structure and function, cell signaling, modulation of the cell's redox state, and cellular respiration.3-5
About 25% of ingested zinc is absorbed by the intestine. Once absorbed, 60% of the zinc is bound to plasma albumin, 30% is bound to alpha2-macroglobulin, and 10% is bound to transferrin ceruloplasmin.6 About 90% of zinc in whole blood is found within red blood cells (RBCs) in the metalloenzymes carbonic anhydrase and copper-zinc superoxide dismutase.1
Ingestion of pennies minted after 1982 is a common source of zinc exposure in dogs.
Zinc is excreted from the body via biliary and pancreatic secretions. Small amounts are excreted by the kidneys into the urine, but most is excreted in the feces.7 Studies have demonstrated that the tissues that contain the highest zinc concentrations in healthy animals are the uveal tract, prostate, bone, skin, muscle, liver, pancreas, and kidney.8 However, extreme excesses of zinc have a deleterious effect on almost every organ system.
SOURCES OF ZINC
Dietary sources of zinc include meat, eggs, dairy products, nuts, seeds, legumes, and cereals. Additional sources of zinc for people can include vitamin and mineral supplements (e.g. multivitamins), cold remedy lozenges, zinc oxide creams and ointments, and acne medications. Zinc chloride-containing products (soldering flux), which are used in stained glass work and can also be found in old window frames, have been reported to cause toxicosis in the human literature.9
Common sources animals are exposed to include pennies minted after 1982, nuts and bolts (galvanized steel) from pet transport cages, zinc oxide creams and ointments, tacks, and clothing and luggage zippers, although any time a metallic foreign body is seen, zinc toxicosis must be a differential.