Hypocalcemia refers to abnormally low calcium levels in the blood serum (a lower concentration than normal levels) or more accurately, a lower than normal levels of ionized calcium in the blood.
As we noted while looking at calcium in cats sources, functions and deficiency, this mineral forms part of bone, teeth, and cartilage and as an electrolyte, it helps in muscle function, impulse transmission, cell signaling among many other functions.
You deserve to know that 99% of the calcium in a cat’s body is stored in bones while the remainder forms part of the extracellular fluid (found outside cells) such as plasma and interstitial fluids.
Of the total blood calcium, the ionized form (iCa) which is the active form accounts for about 55-55%, that bound to albumin protein (pCa) is about 40% while the remainder is found in compounded forms of phosphates, bicarbonate, lactate, citrate, and so on.
Signs and symptoms of feline hypocalcemia
Clinical presentation of hypocalcemia will depend on the severity of the deficiency. Mild cases may be asymptomatic while severe cases will have some symptoms.
At times, you will only notice the various signs once the level of total calcium goes below 6.7 mg/dL. Some of the symptoms that may be noted include:
- Neuromuscular symptoms such as irritability, confusion, disorientation, nervousness, muscle tremors and twitches (involuntary muscle movements including twitching whiskers), hypersensitivity to touch, depression, restlessness, among others.
- Lethargy or weakness
- Stiff gait (limbs extending while the cat is lying down or being stiff) or skeletal deformation characterized by lameness, plantigrade gait and an abnormal posture.
If the deficiency is not corrected, expect severe symptoms such as severe and uncontrollable spasms, seizures (convulsions) and ultimately death.
If you want to remember most of the symptoms, consider the hypocalcemia cats mnemonic that goes like “CATs go numb” that stands “convulsions, arrhythmias, tetany, and numbness in the hands and feet and around the mouth.”
However, some of the neuromuscular symptoms can be due to “primary brain disease, glycogen storage disorders, hepatic encephalopathy, toxins, musculoskeletal disorders,” notes Clinical Endocrinology of Companion Animals Chapter 32.
Animals including cats can regulate ionized cats (iCa) through the interaction of parathyroid hormone (PTH) from parathyroid glands and vitamin D3 or calcitriol.
“Calcitriol acts to enhance calcium absorption into the body from the intestine, promote its release from bone, and cause the kidney to avoid dumping” it, notes Veterinarypartner.vin.com
On the other hand, PHT mobilizes bone calcium (a condition that may lead to osteofibrosis) while still bound to phosphate, but later enhances the dumping of phosphate by kidney while it stops renal calcium removal.
For instance, when the iCa goes amount goes down, the parathyroid glands will detect secrete the parathyroid hormone (PTH) which will, in turn, activate vitamin D3 or calcitriol whose level begins going high.
However, to avoid very high levels of iCa, when vitamin D3 goes high, it shuts down PHT production whose level will begin falling again.
On the other hand, in case of high calcium in cat’s blood (hypercalcemia in cats), the thyroid glands will release calcitonin whose roles is to inhibit this mineral’s intestinal absorption, allow more to be excreted via urine and increase bone osteoblast (cells that cause more bone formation).
Therefore, low calcium in cats has everything to do with too little being provided or any other factor (disease or condition) that will impair its normal absorption, assimilation, resorption or regulation. Common causes include:-
This is characterized by low albumin protein due to kidney failure or any other cause and it results in a decrease in the concentration of ionized blood calcium.
However, this mainly results in asymptomatic hypocalcemia that accounts for about 50% of the cases.
2. Acute and chronic renal failure (CKF)
Under normal functioning, in case hyperphosphatemia (high phosphate in the blood), there will be an increase in reabsorption of calcium that has been filtered inside the kidney while more phosphate is excreted.
However, if kidneys fail, this won’t happen, and high phosphate will reduce iCa levels.
This refers to the absence, insufficient or abnormally low parathyroid hormone produced by parathyroid glands.
Parathyroid tumor, idiopathic hypoparathyroidism (unknown cause), malfunction or removal can be a result. This can result in bone mobilization of calcium, loss through urine, reduced absorption and so on, hence its level in the blood will also go down.
Surgical thyroid glands removal for hyperthyroid cats may result in secondary hypoparathyroidism (postoperative), i.e., have parathyroid glands damaged or accidentally removed during the procedure.
5. Postpartum eclampsia
Also known as feline milk fever, it occurs in nursing cats (or during pregnancy) due to underactive parathyroid gland, poor nutrition such as poor calcium to phosphate ratio, etc., that result in more calcium flowing out through milk while less is either absorbed or resorbed from bones.
6. Phosphate enemas
Designed to help severely dehydrated cats including due to constipation, phosphate in the phosphate enemas may be absorbed which will, in turn, reduce iCa levels.
7. Ingestion of antifreeze
It contains ethylene glycol whose metabolism forms calcium oxalate crystals and, hence low calcium levels in cats.
8. Digestive disorders and malabsorption
Any condition that affects digestion and absorption of calcium including pancreatitis, vitamin D (helps in its absorption inside the gastrointestinal gut) deficiency and rickets, intestinal lymphoma, among others.
This refers to low levels of blood magnesium. Magnesium helps in not only production but also the release of parathyroid hormone that regulates ionized calcium in the blood.
It occurs when body fluids become alkaline and this promotes binding of calcium to albumin. This will cause a low concentration of the ionized form.
11. Puerperal tetany
According to Pet MD, “a clinical neurological syndrome characterized by muscular twitching and cramps and seizures; associated with calcium deficiency (hypoparathyroidism) or vitamin D deficiency or alkalosis,”
12. Other causes
Other possible causes include translocation of calcium intracellularly, certain medications, oxalate or citrate toxicity, rapid chronic hypercalcemia reversal, and nutritional secondary hyperparathyroidism.
Also, chronic starvation, quick phosphate IVs, tumor lysis syndrome, blood transfusion where citrate anticoagulant is used, among others can use this condition.
Your vet will consider your cat’s history especially when symptoms were first noted, whether it is lactating, have had thyroid surgery recently or instances of renal disease, and so on.
After evaluating your cat’s overall physical health for all body systems, your vet may recommend urinalysis, complete blood count (CBC) and blood biochemistry profile to check calcium levels. Also, radiographs may be necessary.
Some of the deductions that may be made from the various tests include the following:
- Azotemia or Elevated BUN (Blood Urea Nitrogen) and creatinine may indicate renal failure, oxalate or ethylene glycol toxicity.
- Blood chemistry may reveal hyperphosphatemia or high phosphate levels in the blood while that of calcium will go low. This could indicate hypoparathyroidism, toxicities (ethylene glycol and oxalate), kidney problems or enema use if constipated.
- Urinalysis may indicate the presence of glucose or low volume of concentrated urine which will indicate kidney problems, oxalate or ethylene toxicity.
- High white blood cells will indicate infections or inflammation while high lipase and amylase may be a pointer to pancreatitis.
- Blood gas analysis may be done to check carbon dioxide levels. High levels indicate alkalosis.
- The biochemistry profile will reveal hypoalbuminemia whose effect we have already discussed.
- CBC will show anemia in case of chronic kidney failure, intestinal malabsorption or nutrition problems that are closely related to secondary hyperparathyroidism.
- Further blood tests for ionized calcium levels and to check for ethylene glycol in case of toxicity may be necessary. There shouldn’t be any of the ethylene glycols in blood.
- Bone and kidney radiographs – Smaller than normal kidney may indicate chronic kidney failure, enlarged acute kidney failure or toxicity especially glycol and oxalate.
- Finally, PTH blood level testing may confirm if your cat has primary hypoparathyroidism something that will need lifelong care. Also, magnesium blood levels may also help in telling if your cat has secondary hypoparathyroidism.
- Finally, there may be tests to evaluable parathyroid gland functions in case of hypoparathyroidism
Treating hypocalcemia in cats
Your feline friend will be stabilized before the underlying cause is treated. Depending on its severity, hospitalization may be recommended for intensive treatment and monitoring.
In case of an emergency, Cat World recommends a “slow intravenous administration of calcium gluconate and diazepam to manage seizures” as well as an electrocardiogram and heart rate monitoring. After this pet has been stabilized, the calcium gluconate can be added to IV fluids until normal serum concentration.
Additionally, your vet may recommend a short or long-term calcium supplementation both oral (such as calcium powders, solutions or powders at 0.5–1 g per day) or through injections. This may be coupled with vitamin D supplementation that could be tablets, capsules, powder or liquid. However, discontinue in case of hypercalcemia.
Finally, depending on the cause, phosphate binders may be recommended (in case of chronic kidney failure), surgery (for pancreatitis), treating poisoning, the use of anti-nausea, pain killers, and so on as well as a regular check of any cardiac problems with an echocardiogram.
Some underlying conditions may require lifelong care such as primary hypoparathyroidism, kidney failure, and so on.
Also, dietary changes may be recommended especially for home-based diets to ensure they have the correct amounts and ratios of calcium and phosphate. Consider sources including ground eggshell, calcium carbonate, calcium lactate, bone meal especially freeze-dried bones among other calcium supplements for cats.