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Hypophosphatemia in Cats

A low concentration of phosphorus in the blood serum can be caused by shifts of phosphorus from the extracellular fluid (the fluid outside of the cells) into the body cells, reduced intestinal absorption of phosphorus, or reduced renal (kidney) phosphorus reabsorption.

In patients that are being treated with insulin for diabetic ketoacidosis (a condition in which the body burns fatty acids and produces acidic ketone bodies in response to insulin shortage, or are undergoing refeeding with glycolysis (synthesized glucose) for treatment of starvation, a resulting rapid production of adenosine triphosphate (ATP, a nucleotide that transports chemical energy within cells) can lead to relocation of phosphorus into cells. If not diagnosed, it can further lead to acute extracellular hypophosphatemia (an electrolyte disturbance).

Because phosphorus is an important component of ATP, low serum phosphorus concentration can cause ATP depletion and affect cells with high ATP-energy demands, such as red blood cells, skeletal muscle cells, cardiac muscle cells, and brain cells. A state of hypophosphatemia can also lead to a reduction in erythrocyte 2,3-DPG, resulting in decreased oxygen delivery to tissues.

Symptoms

Symptoms are generally consistent with the primary disease that is responsible for the hypophosphatemia, rather than any that would be related to the phosphate concentration itself.

• Hemolytic anemia (breaking down of red blood cells) secondary to severe hypophosphatemia
• Red or dark-colored urine due to hemoglobinuria (protein hemoglobin is found in abnormally high concentrations in the urine) from hemolysis (breaking open of red blood cells)
• Tachypnea (slow heartbeat), dyspnea (shortness of breath), and anxiety secondary to hypoxia (shortage of oxygen in the body)
• Muscle weakness
• Mental depression
• Rapid, shallow respirations due to poor respiratory muscle function

Causes

• Maldistribution - enteral nutrition (tube in nose) or total intravenous nutrition
• Treatment of diabetes mellitus
• Carbohydrate loading with insulin administration
• Respiratory alkalosis (reducing hydrogen ion concentration of arterial blood plasma)
• Reduced intestinal absorption of phosphorus - phosphorus-poor diet
• Vitamin D deficiency
• Phosphate-binding agent
• Malabsorption syndromes – conditions which prevent absorption of nutrients
• Reduced renal (kidney) phosphate reabsorption
• Undiagnosed or poorly regulated diabetes mellitus
• Prolonged anorexia, starvation, or malnutrition
• Phosphate-poor diets or intravenous nutrition solutions

Diagnosis

Your veterinarian will perform a thorough physical exam on your cat, taking into account the background history of symptoms  that you have provided, and possible conditions that might have led to this condition. Because there are several possible causes for this condition, your veterinarian will most likely use differential diagnosis to determine the priority for treatment. This process is guided by deeper inspection of the apparent outward symptoms, ruling out each of the more common causes until the correct disorder is settled upon and can be treated appropriately. A complete blood profile will be conducted, including a chemical blood profile, a complete blood count, and a urinalysis.