Home > Symptoms > Phosphorus and Calcium imbalances
Overview
- Phosphorus and calcium are minerals essential to bodily function.
- Imbalances may arise in CKD cats and lead to a condition known as secondary hyperparathyroidism, which may make the CKD progress faster.
Hypercalcaemia (High Calcium Levels)
The symptoms of hypercalcaemia tend to be neurological or related to the kidneys or cardiovascular system. Hypercalcemia in cats (2001) Chew D Presentation to the World Small Animal Veterinary Association World Congress says “The most common clinical signs associated with hypercalcemia in cats are anorexia and lethargy (88%), followed by GI signs, polyuria/polydipsia [increased urination/drinking], urinary, and neurologic signs. Vomiting and polyuria/polydipsia are reported much less commonly in cats with hypercalcemia, as compared to dogs. The magnitude of hypercalcemia is not related to the clinical signs.”
Hypercalcemia in dogs and cats (2016) Peterson ME Merck Veterinary Manual says “Polydipsia, polyuria, anorexia, lethargy, and depression are the most common signs, but many animals with milder degrees of hypercalcemia may be asymptomatic. Constipation, weakness, shivering, twitching, vomiting, stiff gait, and facial swelling are less often reported.”
Seizures
Seizures may be a sign of calcium imbalances. Seizures may take a number of different forms. There may be the classic jerking and loss of consciousness, but being “spaced out” or mentally absent or staring into space may also be a type of seizure.
Seizures in CKD cats may also be caused by high potassium levels, high blood pressure, high levels of toxins, or metabolic acidosis. The use of Reglan (metoclopramide) for stomach problems or Advantage for fleas may lower the seizure threshold.
Other possible causes of seizures include epilepsy or a brain tumour, but the causes mentioned above are far more likely in a CKD cat and should therefore be considered first.
Audiogenic reflex seizures in cats (2016) Lowrie M, Bessant C, Harvey RJ, Sparkes A & Garosi L Journal of Feline Medicine & Surgery 18(4) pp328-336 reports on a particular kind of epilepsy called feline audiogenic reflex seizures (FARS) which was recently identified in cats. This is most often found in elderly (over 15) or Birman cats, and is triggered by high-pitched noises, such as crinkling a paper bag or touching keyboard keys. International Cat Care explains more about this condition. Although phenobarbital is usually used for epilepsy in cats, Levetiracetam in the management of feline audiogenic reflex seizures: a randomised, controlled, open-label study (2017) Lowrie M, Thomson S, Bessant C, Sparkes A, Harvey RJ & Garosi L Journal of Feline Medicine & Surgery 19(2) pp200-206 found that a medication called levetiracetam (Keppra) seems to work better for this condition.
Twitching, Trembling or Shaking
Twitching may be caused by calcium imbalances (especially head twitching). Other causes of twitching include high phosphorus levels, high or low potassium levels, high blood pressure, hyperthyroidism or vitamin B deficiency. Twitching may also be caused by toxin levels. If your cat only twitches while you are giving fluids, it is probably caused by either the type of fluid used or by giving cold (room temperature) fluids.
Pharaoh’s Shakes is a video showing a CKD cat twitching.
Pet MD mentions that twitching may be caused by kidney disease.
Weakness
Weakness may be seen. Another possible cause of weakness is high phosphorus levels leading to secondary hyperparathyroidism. If your cat seems to be clumsy or stumbling, please also read The Importance of Phosphorus Control.
Weakness in the back legs is often caused by low potassium levels or occasionally by low magnesium levels; while muscle wasting may be caused by metabolic acidosis. General weakness may be caused by anaemia. If your cat no longer jumps, this may be thought to be weakness when in fact it is an unwillingness to jump because of blindness caused by hypertension. An inability to jump or climb may also be caused by arthritis.
Eating Litter/Licking Concrete
This is normally associated with anaemia, but is occasionally seen when there are calcium imbalances.
Increased Urination (Polyuria)
This is a very common sign of CKD in cats, but may sometimes be a sign of hypercalcaemia.
Cats with chronic pyelonephritis (a kidney infection or inflammation) may exhibit polydipsia and polyuria.
The ins and outs of polyuria and polydipsia (2003) Osborne CA DVM360 Magazine discusses polyuria.
Increased Drinking (Polydipsia)
This is a very common sign of CKD in cats, but may sometimes be a sign of hypercalcaemia.
Cats with chronic pyelonephritis (a kidney infection or inflammation) may exhibit polydipsia and polyuria, as may cats with diabetes.
Increased drinking may also be a symptom of gastric hyperacidity. The cat may drink more because, according to A glass of water immediately increases gastric pH in healthy subjects (2008) Karamanolis G, Theofanidou I, Yiasemidou M, Giannoulis E, TriantafyllouK & Ladas SD Digestive Diseases and Sciences 53(12) pp3128-3132, drinking water may briefly (only for a few minutes) reduce levels of stomach acid.
The ins and outs of polyuria and polydipsia (2003) Osborne CA DVM360 Magazine discusses polydipsia.
Constipation
This may be caused by high calcium levels. It may also be caused by dehydration or low potassium levels.
Low Temperature
This may be seen when there are calcium imbalances. Other possible causes include anaemia and heart problems. A CKD cat’s temperature may also fall during The Final Hours.
Hypocalcaemia (Low Calcium Levels)
Some of the symptoms of hypocalcaemia are actually often similar to those seen with hypercalcaemia. VCA Animal Hospitals says “Early signs of hypocalcemia include restlessness, stiffness, weakness, irritability, muscle tremors and hypersensitivity (exaggerated responsiveness) to touch and sound. More profound signs include severe generalized muscle twitching, leading on to uncontrolled muscle spasms, seizures and ultimately death.’
Symptoms of Phosphorus Imbalances
Since phosphorus control is so important for CKD cats, there is an entire page devoted to the topic, which includes symptoms of imbalances. Briefly, they include:
- Loss of appetite
- Itching
- Lack of co-ordination in the limbs
- Plantigrade posture
- Teeth grinding
- “Knuckling”
- Weakness
- Weight loss
- Nausea
- Twitching, trembling or shaking
Treatment Options
It is possible to treat all of the above symptoms, in many cases effectively, and details can be found in the Treatments and Phosphorus Binders sections.
This page last updated: 04 May 2025
Links on this page last checked: 04 May 2025