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Pricey medical bills aren't limited to human members of the family. The American Pet Products Association estimates Americans shelled out more than $16.6 billion on veterinary care in 2017. (Pet insurance can help, but it doesn't always make sense.) Even something as seemingly minor as an upset stomach can set you back a few hundred dollars — an average $344 for cats and $292 for dogs, according to data from Nationwide. The pet insurance provider analyzed the data from its more than 650,000 insured pets to see which medical conditions were most likely to have pet owners visiting the vet, as well as the typical bill for treatment. Here are some of the most expensive yet common reasons you and your pet might have to take a trip to the vet.

Diabetes

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Although diabetes is the eighth most-common medical ailment to affect cats, it's the most expensive. Nationwide says cat owners whose pets suffer from diabetes spend an average $889 a year to treat the disease. Dr. Carol McConnell, Nationwide's vice president and chief veterinary officer, said diabetes is expensive to treat because it's a lifelong ailment. Owners must regularly bring their animals to the vet for rechecks and medical monitoring, as well as cover the costs of their cat's insulin. McConnell said if your cat is drinking a lot of water and has a high appetite, you may want to get its blood tested for the disease.

Chronic kidney disease

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Kidney disease is another lifelong disease. It ranks fourth on Nationwide's list of common ailments for cats and is the second-priciest condition, averaging $649 a year to treat. "Most cats, if they live long enough, they will end up with some degree of kidney compromise," McConnell said. When a cat has kidney disease, their kidneys are not properly filtering the blood. To treat this, owners must put their cat on a special diet and bring it for multiple checkups and blood tests to monitor the nitrogen levels in their blood. Warning signs to get your pet checked include lethargy, drinking a lot of water, frequent urination and taking a disinterest to food, McConnell said.

Gum disease

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Periodontitis, or gum disease, made Nationwide's lists for both dogs and cats. It's the second most-common ailment for cats, and costs $434 on average to treat. It's the eighth most common for dogs, with an average bill of $400. McConnell said gum disease is preventable by bringing your pet for wellness checkups. Periodontitis warning signs include yellow tartar on your pet's teeth, pink or red gums and extremely bad breath.

Upset stomach, vomiting

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Treating your cat or dog for a stomachache might give you indigestion: The average bill runs owners $344 for cats and $292 for dogs, according to Nationwide. (It ranks third and fifth, respectively, in terms of common conditions triggering a vet visit.) The high cost is because there are a number of reasons your pet may be vomiting, McConnell said. (For example, parasites, an infection, or a bad reaction from eating something he or she shouldn't.) Diagnostic testing to determine the cause can include blood work and X-rays.

Arthritis

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