Hyperphosphatemia in Dogs

Most phosphorous is stored in the bones, but a small percentage circulates in the blood-normally no greater than 6.0 mg/dL. Its role is in muscle contraction and nerve function, but levels of phosphorous are controlled by the kidneys under the parathyroid hormone (PTH). This hormone prevents levels from rising too high, so if the phosphorous levels are high in your dog, there is likely something wrong with their kidneys.

Hyperphosphatemia is always a marker of an underlying disease because elevated levels in the blood are considered a symptom itself. By itself, it will not cause any clinical symptoms. However, in chronic cases with high phosphorous levels, you may see:

• Excessive thirst
• Excessive urination
• Muscle tremors
• Muscle wasting
• Seizures
• Decreased bone density

Types

Hyperphosphatemia manifests as either an acute or a chronic case.

• It is rare for the acute cases to create long-standing problems as these are most commonly caused by adolescent growth spikes. However, if the cause was due to poisoning, parasites or trauma, it is vital to get your pet to a veterinarian for treatment of the underlying cause.
• In chronic conditions, symptoms will be manifesting over a long period and will give a better idea of the underlying cause, but will more severely affect their health and will present with more symptoms which may be alarming or dangerous in nature - as with muscle spasms and seizures.

The most common causes of this disease varies depending on the dogs age.

• In older dogs, it is most commonly caused by renal failure, intracellular malfunction, a malfunctioning thyroid gland resulting in a decreased production of the parathyroid hormone or overactivity of the gland which results in weight loss and muscle wasting. It may also be linked to diabetes.
• In adolescent dogs, it's often due to increased intestinal absorption and decreased renal absorption. It should be noted that phosphorous levels in young dogs - especially of large breeds will sometimes be greater than in adults because phosphorous is used to facilitate bone mineralization (hardening). This is normal.
• In all age groups, it can be caused by dehydration, parasites, trauma, or poisoning caused by raisins/grapes or an excess of vitamin D.

If your dog is displaying twitchy muscles, drinking an inordinate amount or is increasingly lethargic, it's important to get them to a veterinarian office. Be certain to give a thorough history of any symptoms to your veterinarian including duration of symptoms and additional diseases if applicable. Your veterinarian will then conduct a physical exam to determine what organs have been most affected.

In doing a diagnostic analysis, your veterinarian must first determine that your dog, in fact, has high phosphorous levels. This is typically done with a CBC or complete blood count, followed by a serum biochemistry panel and urinanalysis. It should be noted that an exacerbatory factor for hyperphosphatemia include problems with intracellular uptake of phosphorous. If a large number of blood cells die (hemolysis) during or after the blood sample is taken, these cells will release the mineral into the blood serum and therefore have the potential to give a false-positive high reading of phosphorous. For the pet owner, this means that more samples may be necessary to determine actual readings because hemolytic samples are not representative. The importance of this will matter most if your dogs readings are borderline.

High levels of phosphorous due to malfunction of the kidneys or a decrease in the volume of plasma won't necessarily be of clinical significance. Treatment will depend a great deal on the cause of the hyperphosphatemia. If your dog has decreased parathyroid hormone levels, your veterinarian will discuss thyroid hormone therapy.

If the problem stems from renal (kidney) problems, this will first be treated with aggressive fluid therapy followed by a low phosphorous diet to treat a dog with chronically high phosphorous levels. It's also possible your veterinarian will prescribe phosphate binders to link free-floating molecules. Phosphorous and calcium bind to create your dog's bones, so in a dog with high levels of phosphorous, it is possible they will also need to minimize calcium intake. This is especially true of chronic cases because calcium binding with phosphorous in extraskeletal tissue can result in tissue mineralization. This can be fatal.

Visit your veterinarian regularly for checkups to evaluate treatment efficacy. This will usually include taking additional blood samples. Give your dog plenty of quiet and time to recover from an episode of high phosphorous levels. If the underlying cause was an acute case of Vitamin D over supplementation or ingestion of grapes or raisins with minimal damage to their renal system, your dog is likely to recover quickly. If your dog has a chronic condition involving their thyroid gland, renal retention, diabetes or cancer, your veterinarian will discuss a long-term prognosis and management program with you.