15: Calcium and Phosphorus

Hormones that controls Ca⁺⁺ and P

PTH, Vit D, and Calcitonin

PTH action

Increased Ca⁺⁺ and decreased P

Vit D action

Increased Ca⁺⁺ and increased P

Calcitonin action

Decreased Ca⁺⁺ and decreased P

Which hormone is utilized by the rodenticide that mineralizes organs

Vit D (calcitriol)

Problems that happen when Ca⁺⁺ changes

AP derangements

Symptoms of hypocalcemia

Flaccid Paralysis

How is eclampsia different than normal hypocalcemia

Associated with parturition, stiff and tremoring instead of flaccid paralysis

Symptoms of hypercalcemia

• PU/PD: Ca⁺⁺ inhibits ADH

• Tissue mineralization: complexes with P

• Decreased tissue excitability

Where is most of the Ca⁺⁺ in the body

Bone

Most abundant form of Ca⁺⁺ in the blood

Bound to albumin

Secondary form of Ca⁺⁺ in the blood

Ionized Ca⁺⁺

Function of ionized Ca⁺⁺

Available for reactions and hormonal regulation

Ca⁺⁺ fraction measured in a chemistry panel

All of the blood Ca⁺⁺

Test used to measure the active/available Ca⁺⁺

I-stat ionized Ca⁺⁺

Affect of protein levels on Ca⁺⁺

If there is low albumin there is low Ca⁺⁺ → the loss in protein bound Ca⁺⁺ is not replaced by more ionized Ca⁺⁺

What should you do if you have a hypoalbuminemic patient with low Ca⁺⁺

Run an ionized Ca⁺⁺ to see if the patient actually has low Ca⁺⁺

Most common cause of hypocalcemia

Low albumin

Almost outdated equation to estimate if albumin is the cause of low Ca⁺⁺

Corrected Ca⁺⁺

Ca⁺⁺ concentration is most kidney disease cases

Low

Which species has high Ca⁺⁺ in kidney disease

Horses

Why does kidney disease result in low Ca⁺⁺

• Low Vit D production

• Increased P from renal disease complexes with Ca⁺⁺ further dropping the Ca⁺⁺

Pathogenesis of renal secondary hyperparathyroidism

Low Ca⁺⁺ from renal disease → PTH release to try to fix the problem → can’t be fixed without vit D → persistent PTH release

What would be the cause of renal failure in a horse that also displays low Ca⁺⁺

Blister Beetle (cantharidin)

Symptoms of cantharidin toxicity

• Acute renal failure (very sick)

• GI ulcers

• Marked hypocalcemia

Symptoms of ethylene glycol toxicity

• Marked hypocalcemia (Ca⁺⁺ gets bound up by metabolites)

• Calcium oxalate monohydrate crystals

Common handling/artifactual cause of VERY low Ca⁺⁺

K/EDTA tube for a chemistry profile

Most common cause of hypercalcemia

Hypercalcemia or malignancy

T/F: primary hyperparathyroidism is uncommon in dogs

True

Common cause of primary hyperparathyroidism

Benign adenoma

Primary finding associated with primary hyperparathyroidism

Marked increased Ca⁺⁺ and low P

Cause of hypercalcemia of malignancy

PTH related peptides (PTHrP) released from a non-parathyroid tumor

How to tell the difference between primary hyperparathyroidism and hypercalcemia of malignancy

Test for PTHrP

Primary causes of hypercalcemia of malignancy

Lymphoma and AGASACA

Which species has incidental calcium carbonate crystals and why

Horses; they excrete most of their Ca⁺⁺ in the urine instead of feces

Causes of hypervitaminosis D

Cholecalciferol rodenticides and psoriasis cream (random)

How does hypervitaminosis D cause hypercalcemia

It increases Ca⁺⁺ and increases P

How is cholecalciferol rodenticide different than vit K antagonist rodenticides

Cholecalciferol causes tissue mineralization, vit K antagonists cause bleeding