IDIOPATHIC HYPERCALCEMIA
Disease Overview:
Idiopathic Hypercalcemia is a disease in cats of unknown cause that is characterized by increased ionized
calcium values. Often affected cats show no symptoms. Over time, symptoms may develop because the high
calcium levels can cause kidney damage, the formation of calcium containing urinary tract stones, and intestinal
problems including vomiting and constipation. It is recently becoming an increasingly common diagnosis in cats
of all ages.
CLINICAL SIGNS AND DIAGNOSTIC TESTING
Many affected cats have no symptoms; up to 46 % may not show any clinical signs. However, vomiting, weight
loss, painful urination, poor appetite, constipation, and inappropriate urination have been reported in some cats.
Bladder or kidney stones are found in some cats.
Serum ionized calcium should be measured in all cats with urinary tract stones, weight loss,
constipation, and vomiting.
Initial routine serum chemistry panels show an elevated total calcium level that is over 10.8 mg/dl, but
usually less than 13 mg/dl. Total calcium is only an estimate of ionized calcium. An elevated total calcium does
not confirm the condition, but raises the suspicion and indicates a need for recheck and further testing. The
Serum phosphorus level is usually normal unless chronic renal failure is already present. Kidney function blood
tests are usually normal initially, but chronic renal failure may develop in some cats, particularly if the calcium
stays elevated long term.
When a routine serum chemistry panel reveals increased total calcium levels, Ionized Calcium
measurements must then be done to confirm if significant and true Hypercalcemia is present. Ionized
Calcium tests require special handling and are more expensive so they are not included on routine blood
panels.
When the confirmatory Ionized Calcium test is run, it is also found to be increased. Sometimes the
increased ionized calcium levels are found to be out of proportion to the degree of increase in total serum
calcium (e.g. some cats may have a total serum calcium concentration within normal or just 0.1 mg/dl above
normal, yet have significant elevation in ionized calcium). A large study in cats demonstrated discordant findings
when total serum calcium was used to estimate serum ionized calcium. Checking the ionized calcium level is
important.
OTHER TESTS THAT SHOULD BE CONSIDERED TO CONFIRM IDIOPATHIC HYPERCALCEMIA
INCLUDE:
Serum Parathyroid Hormone (PTH) concentration is usually in the normal or low range. Idiopathic
Hypercalcemia is a parathyroid independent hypercalcemia. The Parathyroid gland should not involved.
Serum Parathyroid-related protein (PTHrp) concentration (which is a screening test for some cancers that
cause high blood calcium) should be checked and should be undectable or Zero in this condition.
Urine specific gravity or urine concentration tests of kidney function usually demonstrate well concentrated
urine unless kidney failure is already present.
Imaging via radiographs (x-rays) or ultrasound should be done to rule out obvious tumors and cancers that
can cause high ionized calcium. Imaging may also show kidney or bladder stones, presumably developing due
to the increased urinary calcium excretion.
Etiology or Cause: Idiopathic or unknown
Treatment/Management/Prevention:
1. Because the cause is unknown, an effective or specific treatment that works in every cat has not been
identified.
2. Dietary modifications may lower serum calcium concentrations in a small number of cats. These
modifications may include using a high fiber diet, or one that is less acidifying. High fiber diets may make less
dietary calcium available for intestinal absorption. Unfortunately dietary therapy is often unsuccessful.
3. Glucocorticoids (steroids) are often recommended for cases that don't respond to dietary change.
Glucocorticoids decrease intestinal calcium absorption, reduce bone resorption, and increase calcium excretion.
Prednisolone:
 Start with 5 mg/cat/day
 At one month, serum ionized calcium should be rechecked.
 If within normal limits, continue same dose for several months.
 If hypercalemia persists, or re-develops, the dose is increased to 10-20 mg/cat/day.
 Some cats may not benefit.
 Prednisolone has some side effects including increased risks of immunosuppression including urinary
tract infections, and Diabetes.
 Previous research raised concern that steroids reduce tubular re-absorption of calcium and enhance
calcium excretion into the urine potentially increasing the risk of calcium oxalate urinary tract stones to
form. However, more recent research using prednisolone in normal cats did not demonstrate this as an
adverse effect.
4. Bisphosphonates are a newer treatment showing some promise. They assist in lowering serum calcium by
reducing the number and action of osteoclast cells that release calcium from bone.
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Fosamax (alendronate):
10-30 mg once weekly by mouth per cat. The cat must be fasted for 12 hrs prior to giving, and for 2 hrs
after for optimal absorption.
In a pilot study conducted at The Ohio State University Veterinary Hospital, some cats required up to 30
mg weekly to achieve normal calcium levels.
Care should be taken to ensure that tablet medication does not stick in the esophagus, as this is a
known risk for erosive esophagitis in humans.
Giving Tap water orally via a syringe following pilling is recommended to help lessen this possibility.
Also recommended is "buttering" of the lips or paw top to encourage licking, salivation, swallowing, and
increased transit of pills into the stomach.
Blood levels should be rechecked after about 4 weeks of administration and periodically long term. In
many cats the dose needs to be increased or titrated upward from 10 mgs to 30 mgs to control the
calcium.