A penny is not a coin to a cat; it is a 2.5 g zinc tablet with a thin copper coat. Coins minted in the United States from 1982 onward are 97.5% zinc and 2.5% copper, so one swallowed penny carries about 2.44 g of zinc. For a 4 kg cat that is 610 mg per kg, several times the 50 to 100 mg per kg where zinc toxicosis starts. Stomach acid strips the copper within hours, zinc enters the blood, and red cells begin to burst. An abdominal radiograph today is worth more than a week of watching.
Two sources: coins and hardware
The first source is coinage. US pennies from 1982 to the present are 97.5% zinc, and a 1 cent coin weighs 2.5 g; pre-1982 pennies are 95% copper and far less dangerous. Many foreign coins are zinc-based too, and a coin that sticks to a magnet is usually steel, not zinc. The second source is zinc-plated hardware: nuts, bolts, washers, screws, galvanized cage clips, hinges, zipper pulls, cheap jewelry, and the metal base of some cat toys. A single zinc-plated nut can carry 1 to 3 g of coating, and a galvanized cage clip holds enough zinc to poison a cat that licks it for a few minutes. Pennies, washers, and clips all look like toys on a floor.
What zinc does to a cat's blood
Zinc is a direct oxidant for the red cell. It damages the cell membrane and denatures hemoglobin into Heinz bodies, which the spleen then removes, so the cat becomes anemic from the inside. Zinc also irritates the stomach lining, which is why vomiting appears first, often within 2 to 6 hours of ingestion. At the same time zinc blocks copper absorption and can trigger pancreatitis. The dangerous part is the timing: the coin sits in the stomach, dissolves slowly, and keeps releasing zinc for as long as it stays there, so a cat can look stable at hour 8 and be pale and weak at hour 30.
The 24-hour line
Hemolysis is not instant. Heinz bodies start forming within 6 to 12 hours, but the hemoglobin drop that shows on a blood count usually peaks between 24 and 72 hours, and that is the window where a cat can crash. The 24 hour mark is the first recheck: a packed cell volume that has fallen by more than 10% from baseline, or hemoglobin under 8 g/dL, means the cat needs hospital care now. Vomiting that starts within the first 24 hours is often blamed on the anesthesia or on an upset stomach, and the anemia gets missed on the second day. Any cat with a missing coin and vomiting at 24 hours needs a blood count, not a change of food.
Two tests that confirm it
The first test is a complete blood count with a Heinz body check and a reticulocyte count; Heinz bodies appear as small blue bumps on the red cells under a stained smear, and the reticulocyte count tells you whether the bone marrow is responding. The second test is serum zinc, taken in a trace-element tube, because zinc leaks out of ordinary tubes and a normal result from the wrong tube means nothing. A chemistry panel adds pancreatic and kidney values, and an abdominal radiograph or ultrasound finds the coin itself, which is the only finding that proves the exposure and the only one that leads to removal.
How much zinc is too much
| Object | Zinc content | Dose for a 4 kg cat | Expected effect |
|---|---|---|---|
| US penny, 1982 or later | 2.44 g | 610 mg/kg | Hemolysis within 24 to 72 hours |
| US penny, before 1982 | 0.12 g | 30 mg/kg | Usually passes, still needs an x-ray |
| Zinc-plated nut, 3 g coating | 2.5 g | 625 mg/kg | Vomiting, anemia, pancreatitis |
| Galvanized cage clip | 1.5 g | 375 mg/kg | Vomiting within 6 hours |
| Zinc oxide ointment, 40 g | 16 g | 4000 mg/kg | Severe, often fatal without care |
Signs, and what must send you out the door
Early signs are vomiting, drooling, loss of appetite, and abdominal pain when you touch the belly. Later signs are pale gums, weakness, fast breathing, dark urine from hemoglobin, jaundice, and collapse. Go to an emergency clinic immediately for pale or white gums, a heart rate above 240, labored breathing, or dark red urine, because those 4 signs mean the cat is bleeding red cells faster than the bone marrow can replace them. A cat that swallowed a penny and is still normal at 6 hours is not safe; it is early.
Hospital care for a cat passing hemoglobin includes fluids and often a urinary catheter, and the at-home part is covered in our catheter aftercare guide; to turn a washer or a coin into a dose, use the poison dose tool.Removal and treatment
A coin still in the stomach is usually pulled out with an endoscope or with surgery, and removal stops the zinc load at the source. Treatment after removal is supportive and prescription-based: intravenous fluids, an antiemetic, a gastroprotectant, and a blood transfusion if the packed cell volume falls below roughly 15%. Chelation is not the answer for zinc in the stomach, because the metal has to come out first. All drugs are given by veterinary prescription. Most cats that have the coin removed within 24 hours recover in 3 to 5 days; cats that keep the coin for a week often need a transfusion.
Keeping metal off the floor
- Count the coins in the coin jar and keep it in a drawer, not on a table or in an open bowl.
- Replace zinc-plated nuts and washers on cat furniture with stainless steel, and check cage clips every 3 months.
- Sweep under the sofa and the fridge once a week, where coins and screws collect.
- If a coin is missing and the cat is vomiting, go for an x-ray the same day rather than waiting for anemia.
- Ask for a Heinz body check by name; a routine blood count alone can miss it.
Frequently asked
How dangerous is one penny to a cat?
A US penny minted from 1982 on contains about 2.44 g of zinc, which is roughly 610 mg per kg for a 4 kg cat, several times the 50 to 100 mg per kg where zinc toxicosis begins. The coin must be found and removed; it keeps releasing zinc for as long as it sits in the stomach.
Why does the vet want to wait 24 hours before repeating blood work?
Heinz bodies form within 6 to 12 hours, but the hemoglobin drop that shows on a count usually bottoms out between 24 and 72 hours. A normal count at hour 6 does not mean the cat is safe, and a recheck at 24 hours is what catches the hemolysis before the cat collapses.
Can a zinc-plated nut cause the same poisoning as a coin?
Yes. A single zinc-plated nut or a galvanized cage clip can carry 1.5 to 3 g of zinc, which is in the same range as a penny for a small cat. Any missing hardware plus vomiting or pale gums deserves an x-ray and a blood count the same day.