I routinely encourage my clients to run lab work on their apparently healthy animals during their annual wellness checkups. Why? Because there are so many things that we can learn from blood work and urinalysis results that can help us to address problems, both pressing and potentially so, before they become serious.
This is especially important in cats, who seem to keep matters of their health as closely guarded as secrets of national security.
One of the most common abnormal lab results I encounter in apparently healthy cats is high serum calcium. “Hypercalcemia,” as it’s called, means abnormally high blood calcium levels. It’s important to find the cause for two reasons. One, the primary or inciting one can be a serious issue, such as cancer, and two, if the cause is not found and addressed the excess calcium in the blood isn’t easily excreted by the body. It starts looking for a place to deposit itself, and that usually means soft tissues like the kidneys and lungs, which have other very important jobs to do that are hindered by random deposits of calcium.
In vet school students like to make up mnemonic devices to help them remember at least some of the copious amounts of information that are taught. The one we use to remember the causes of hypercalcemia is “GOSHDARNIT” – cute, I know, but it works during those eight-hour national veterinary board exams.
Gimme a “G”!
“G” stands for granulomatous disease, which is a huge mouthful but is really just another name for the class of diseases caused by fungus. These types of diseases aren’t present in all areas – they tend to thrive in locations that get a lot of rainfall.
Most of the times cats with fungal diseases, aren’t normal, and they don’t feel well, but occasionally we find these diseases when we didn’t know anything was wrong. Remember, cats are very good at hiding disease from us, and that’s why it’s very helpful to do routine lab work periodically.
Gimme an “O”!
“O” stands for osteolysis, which means bone destruction. You can imagine that if bone is being destroyed, the components of bone such as calcium, would circulate at higher levels in the blood. Cats can have a form of cancer called multiple myeloma, which often results in destruction of bone.
Gimme an “S”!
Love this one. It stands for “spurious”, meaning the lab made an error. This one goes away when you check the calcium levels a second time. It’s not that common, so if we can’t find any other causes, we repeat the calcium levels to see if the elevation is persistent or not.
Gimme an “H”!
The “H” in this adorable game stands for hypoadrenocorticism, which is another name for Addison’s disease. Addison’s disease occurs when the adrenal glands, the tiny but important glands that sit on top of the kidneys, stop producing some very important hormones. Addison’s is almost solely a disease of dogs (and President Kennedy, interestingly enough), but it can occur in cats as well.
Vitamin D toxicity
Calcium and vitamin D are inextricably linked in the body. When there are high levels of vitamin D in the blood there are often high calcium levels as well. Sometimes owners will supplement their cat’s vitamin D intake excessively, and this will cause hypercalcemia. Commercially manufactured cat foods have appropriate vitamin D levels, so this isn’t a problem if the cat is eating a typical feline diet.
“A” is for Addison’s
Sorry, that one’s a repeat. No mnemonic is perfect!
“R” is for renal
Renal disease is a very common problem in older cats. The kidneys play a big role in the regulation of calcium and phosphorus in the body, and when the kidneys fail, there are often abnormally high levels of calcium in the blood, because the kidneys aren’t excreting it properly.
In addition, hypercalcemia causes kidney failure, so it’s kind of a chicken-and-the-egg thing. Did the kidney failure make the calcium go up, or did the high calcium make the kidneys fail? That has to be figured out.
“N” is for cancer
Right, I know “cancer” starts with a “c”, but doctors call cancer “neoplasia”. Several types of cancer can cause high calcium in the body, specifically lymphoma (cancer of the lymphatic system), parathyroid gland adenocarcinoma (cancer in the small glands in the neck that regulate calcium), anal sac adenocarcinoma (cancer in the glands around the anus), and multiple myeloma (another type of blood cell cancer). Lymphoma is by far the most common cancer that causes high calcium in cats.
“I” is for “I’m an idiot”
Not really. “I” stands for “idiopathic”, which means we’ve looked everywhere and we can’t find a cause. It turns out that idiopathic hypercalcemia is a very common cause of hypercalcemia in cats.
“T” stands for “toxin”, which is typically due to ingestion of a rat poison that causes wildly elevated vitamin D levels. Again, really, really uncommon in cats.
Let’s go back to idiopathic hypercalcemia, and what we do when we find hypercalcemia on the blood work of otherwise normal cats. We might be keen to chalk up the hypercalcemia we find to “idiopathic”, but doing so is dangerous, since we might be ignoring some very serious diseases.
Some things – like bone cancer (lack of pain), kidney disease (lack of elevated kidney values on blood work), and poison ingestion or dietary abnormalities (from the history the owner gives) – can be ruled out right away. Then the job becomes looking for cancer by taking chest x-rays, performing an abdominal ultrasound, carefully examining the anal glands, and running special blood tests on the parathyroid glands.
If a cause of hypercalcemia is found, the next step is to treat that cause, if possible, and by doing so the elevated calcium should come down. If all the tests are normal, and a recheck of the calcium proves that it’s still elevated, then we can call this “idiopathic hypercalcemia”. Unfortunately, although idiopathic hypercalcemia has been studied quite a bit, there’s not a lot of consensus about what works and what doesn’t work to bring calcium levels down. Typically we turn to diets that are relatively low in calcium and high in fiber. These help in some cases, but not in all cases.
If idiopathic hypercalcemia cannot be controlled with diet, it’s important to monitor organ function, to ensure that high calcium levels aren’t starting to affect them.