Excess Phosphorus in the Blood in Cats

Excess phosphorus in the blood, or hyperphosphatemia, is most often a side-effect related to the malfunction of other bodily systems. Since the kidneys are responsible for regulating blood phosphorus levels, kidney disease is commonly suspected when a cat is presented with hyperphosphatemia. Other causes may include bone disease, cancer, hyperthyroidism, calcium deficiency or improper diet. Since hyperphosphatemia can only be treated effectively once the underlying cause is discovered, your veterinarian will need to perform appropriate diagnostic tests prior to initiating treatment.

Phosphorus is a mineral that is necessary in the regulation of many critical processes in the body. The majority of the phosphorus in a cat's body is bonded with calcium to form calcium phosphate, which is utilized in the creation and maintenance of healthy bones and teeth. The portion of phosphorus not contained in skeletal tissues circulates in the bloodstream to assist in metabolic processes such as normal muscle and nerve activities. Excess phosphorus in the blood does not often produce specific, dramatic symptoms that lead to a simple diagnosis, but it is generally noticed through poor appetite, weight loss, muscle weakness, and lethargy.

A cat experiencing elevated blood phosphorus levels, regardless of the underlying cause, will almost always act as though it feels generally unwell, even if specific symptoms are difficult to pin down. While your cat may not exhibit all of these symptoms, those most commonly reported include:

• Lack of appetite
• Nausea or vomiting
• Unexplained weight loss
• Weakness
• Depression or lethargy
• Excessive thirst
• Rubber jaw (weakening of the bones due to excess blood phosphorous, causing tooth loss and soft jaw bones)
• Muscle tremors
• Twitching

In a healthy body, calcium and Phosphorus levels are maintained by the kidneys at the proper ratio to support normal metabolic functions. Hyperphosphatemia occurs when there is too much phosphate or too little calcium available. The issue is frequently associated with chronic problems like kidney disease or diabetes, but sometimes the cause can be more acute, as in the onset of infection or the ingestion of poison. Common triggers include: 

• Kidney disease
• Kidney infection
• Hyperthyroidism
• Urinary tract blockage
• Bone cancer
• Osteoporosis
• Circulatory problems, typically from heart disease
• Diabetes
• Malfunctioning pituitary gland
• Excess vitamin D intake (dietary overdose or improper supplementation)
• Ingestion of toxic substance (rodent poison or antifreeze)
• Tissue trauma (massive injury, as in being struck by a car

Accurately diagnosing excess phosphate in your cat's blood will require a trip to the veterinarian. Your vet will begin the evaluation based on your cat's age and history. Older cats sometimes develop what are considered to be age-related issues such as kidney disease or thyroid problems that can lead to hyperphosphatemia. Young cats are less likely than older ones to suffer from chronic diseases, but may be more prone to have ingested a toxic substance. 

After taking into account your cat's age and environment, your veterinarian will ask you about your cat's symptoms, habits and diet. To accurately diagnose excess phosphate in the blood, as well as the potential underlying causes, your veterinarian will perform diagnostic tests, including:

• General physical exam
• Blood tests
• Urinalysis
• Bone X-rays
• Kidney X-rays

During the general exam, your veterinarian will be interested in information that you can provide about your cat such as changes in eating habits, increased or decreased thirst, diminished energy level, vomiting, tremors or twitching. Blood and urine samples will be checked not only for phosphate and calcium, but for evidence of thyroid malfunction and diabetes. Bone X-rays can show bone abnormalities such as cancer, tumors or osteoporosis, while kidney x-rays reveal the size and symmetry of the organs responsible for maintaining proper blood phosphate levels.

IV fluids may be administered immediately to bring electrolytes back into balance, with follow-up therapies prescribed based on the underlying cause of the hyperphosphatemia. 

• Kidney disease: While kidney disease cannot be cured, it can often be managed and its progression slowed with a prescription diet that contains high-quality protein and is low in phosphate. Supplements such as aluminum hydroxide or calcium citrate may be added to the diet. Such compounds bind to phosphorus so that it can be safely excreted by the bowels, and should only be given under the supervision of a veterinarian.
• Hyperthyroidism: Medications exist that help support proper thyroid function. Maintaining correct thyroid hormone levels reduces the likelihood of recurring hyperphosphatemia.
• Bone disease: Osteoporosis, bone tumors, bone cancers and other abnormalities causing calcium resorption must each be treated individually. Your veterinarian will prescribe the appropriate course of treatment based on your cat's diagnosis.

High blood phosphate levels stemming from toxins or trauma may disappear once the initial emergency is over. Chronic conditions, however, require long-term care and maintenance, usually including a strictly controlled diet accompanied by daily medications. A routine schedule of blood and urine tests will be necessary to monitor blood phosphorus levels, and medications adjusted as necessary.