L16b: Phosphate Pathogenesis and Lab Evaluation

Which form of phosphate is routinely measured in standard blood tests?

Inorganic phosphate (Pi).

Are organic phosphate forms like ATP and nucleic acids directly measured in routine blood assays?

No; organic phosphate is not directly measured.

What are the three physiological roles of inorganic phosphate mentioned?

Energy metabolism, bone mineralization, and cellular signaling.

PTH release is stimulated by…

1. low blood calcium

2. vitamin D levels change

what does PTH do?

causes bone to release phosphate and kidneys to excrete more phosphate

how does vitamin D affect phosphate?

enhances phosphate absorption from diet

what is a hormone that affects phosphate levels in cell and blood?

phosphate

which age of animal will have a mild increase in phosphate? (this is normal)

puppies and kittens

Where does activation of vitamin D occur to increase gut phosphate absorption?

In the kidneys (conversion to 1,25-dihydroxyvitamin D).

What is the net effect of PTH on phosphate handling in the body?

Bone releases phosphate into blood; kidneys excrete more phosphate by reducing reabsorption.

What gut process is enhanced by active vitamin D regarding phosphate?

Absorption of dietary phosphate from the gut.

What roles does bone play in phosphate homeostasis?

Bone acts as a major reservoir and releases phosphate into the blood when stimulated by PTH

Why might young growing animals have higher phosphate levels?

Bone growth increases phosphate turnover and release.

what does insulin do to phosphate?

drives phosphate into cells

What artifact can falsely elevate serum phosphate levels in a sample?

Hemolysis, causing an artefactual shift from ICF to ECF.

hyperphosphotemia causes

1. excess dietary intake or phosphate enemas

2. reduced renal excretion

3. hypoparathyroidism

4. hemolysis

hypophosphotemia causes

1. tube feeding cats

2. decreased intake

3. renal losses (hyperparathryoidism or pseudohyperparathyroidism)

4. insulin therapy

5. milk fever or eclampsia

hypoparathyroidism

decreased PTH leads to increased tubular reabsorption of phosphate

What is a reported reason some hyperthyroid cats have higher phosphate?

Increased renal tubular phosphate resorption.