Have a Vet 101 Question? Send it to email@example.com with as much detail as possible and a photo.
Where Did All This Calcium Come From? By Dr. Letrisa Miller DVM
Just this week I had yet another cat come through my door with high blood calcium levels, or hypercalcemia. I’ve been seeing this much more in the last year and it has got me thinking about what might be causing the problem in these cats. I have actually seen more cases of hypercalcemia in the last year in my new practice in Connecticut than I saw in the entire 12 years I had my clinic in Oklahoma. Does the problem have a correlation with geographical location? My research shows no studies that address this possibility, so the veterinary community doesn’t seem to have looked at whether or not there could be a connection. The truth is, in most cases, we don’t know what the cause is, so it is very hard to get a handle on what the risk factors might be.
Why is it important if your cat has high calcium levels? The most important reason is that it makes them feel lousy. Just a little extra calcium can severely affect appetite and start causing kidney damage. If calcium levels get too high, the soft tissues of the body also start to calcify, or turn to bone. If a cat’s levels are very high, it will have to be hospitalized and given IV fluids to flush the calcium out of its body until a means of controlling the cause can be found. Hypercalcemia can be life threatening in the short or long term. In the short term it can cause heart arrhythmias and severe kidney damage as well as neurological dysfunction. In the long term it is very damaging to the kidneys and causes kidney calcification and stones as well as damage to many other organ systems.
How is hypercalcemia diagnosed? Routine blood tests are used to measure total calcium levels in blood. Many veterinarians can run this test in their hospital or clinic while you wait. When a high total calcium level is detected, a second test is usually run to confirm that a problem exists. This test is for ionized calcium. Your veterinarian won’t be able to run this test in house, so it has to be sent to a specialized lab and may take some time to get results. If the ionized calcium is high, then most doctors will ask for a parathyroid hormone level and parathyroid-like protein level as well.
If hypercalcemia is confirmed, a reason for the problem is looked for so that an appropriate treatment can be started. This leads to the question: How does hypercalcemia in cats happen?
Several control mechanisms are responsible for calcium blood levels, but I like to think of the problem in terms of the question “where is the calcium coming from?” Extra calcium can be coming from absorption of too much calcium, mobilization of the body’s calcium stores, or failure to remove excess calcium from the body through the kidneys.
The first of these possibilities, too much being absorbed, is most commonly caused by too much activated vitamin D (calcitriol), causing the intestines to absorb too much calcium. When this happens, phosphorus is usually high as well. Hypervitaminosis D has several causes, including exposure to prescription psoriasis cream (Dovonox) or one type of rodent poison. Too much vitamin A can also be a contributor.
Mobilization from calcium stores occurs when there is bone disease like infection, inflammation, or too much parathyroid hormone; it can also occur when cancerous tumors or benign granulomas (inflammatory masses) produce proteins that are similar enough to parathyroid hormone that they act in the same way as the real hormone. In cases with too much parathyroid hormone, phosphorus is usually low.
Failure to remove calcium through the kidneys happens when there is a specific failure of the kidney or a deficiency of mineralocorticoids (hypoadrenocorticism). Mineralocorticoids are made in the adrenal glands along with other hormones such as cortisol and adrenaline. Low sodium and high potassium are usually also found in hypoadrenocorticism cases.
In cats with kidney disease, it can be very difficult to determine if the kidney disease is causing the high calcium, or if the high calcium has caused kidney damage.
The causes of hypercalcemia can be complex and are hard to untangle in many cases. Because of the complexity and confusing nature of calcium controls in the body, I won’t go into the details of figuring out which cause is likely in individual cases.
- The most common cause of high calcium levels in cats is unknown—the medical term is “idiopathic,” and basically it means we’re too idiotic to figure out the cause! Thus, my frustration with hypercalcemia. How do you do anything other than put a bandage on a problem when you have no clue as to the cause?
- One of the recent thoughts about idiopathic hypercalcemia is that the cause might be related to diet, that we might be causing the hypercalcemia by feeding cats a diet that is not similar to what they naturally eat. Because of this, one approach to treatment has been to put cats on homemade high-protein, grain-free diets. Thus far, I have not found much success with this approach, but that may be because most people don’t have the time or inclination to cook for their cats. (That said, two packs of kangaroos are waiting in my kitchen for me to cook food for my multiply allergic cat, Monster. Who says you can’t make time to feed your cats homemade?) The jury is still out on dietary management of hypercalcemia, but it is certainly worth a try.
- Some cats that have granulomatous disease or inflammatory disease will respond to prednisolone therapy, but they tend to require high doses and often the therapy only works for a short time.
- Fosamax, a bis-phosphate that stops breakdown of bone by normal bone cells called osteoclasts is the last line of defense. I have had to resort to this drug in several patients. It is a difficult drug to give because it is caustic and must be given on a totally empty stomach to be effective. This means fasting for 12 hours before medicating and giving lots of water with the pill to make sure that it doesn’t stay in the esophagus and cause damage. Fosamax is not a great option, but it is the only choice we have for those cats that don’t respond to prednisolone or diet change. In human beings who take the drug for many years, one side-effect of Fosamax is brittle bones. Whether extended use of the drug will have the same effect in cats is not known.
- Hypercalcemia, the malfunctioning of the body’s calcium-regulation system, is a symptom of a number of diseases—this is what makes it so frustrating. Treating it successfully is difficult if the underlying cause can’t be found, and if left untreated it results in death in most cases. Idiopathic hypercalcemia is the most common form seen today and seems to be increasing in frequency; it is also by far the most difficult to treat because we can only treat the symptom if we don’t know the cause.
The good news is that hypercalcemia isn’t nearly as frustrating to cat owners as it is to veterinarians, because we do have some effective treatments to keep hypercalcemic cats feeling well for a long period of time. Hopefully our understanding of the reasons cats become hypercalcemic will improve in the near future so that we can better identify and treat it.
For more information and to visit her website, Dr. Letrisa Miller has a feline-only practice in Connecticut