Calcium, Phosphorus, Magnesium Clinical Pathology

Front 1

When is parathyroid hormone released?

Back 1

In response to hypocalcemia and to some extent hypomagnesemia

Front 2

What are the overall results of parathyroid hormone?

Back 2

Increases calcium
Decreases phosphorus

Front 3

What are the 4 ways the parathyroid hormone acts to increase serum calcium and decrease serum phosphorus?

Back 3

1) Increased calcium release from bone
2) Decreases phosphorus resorption by kidneys, thus excreting more phosphorus
3) Increases activity of Vit D by accelerating formation of active form
4) Increased calcium absorption from gut and distal renal tubules

Front 4

What produces parathyroid-related protein (PTH-rP)? What does it do?

Back 4

Similar actions as PTH and is abnormally produced by some neoplastic cells

Front 5

What produces calcitonin and when is it produced?

Back 5

Thyroid parafollicular cells (C cells) in response to hypercalcemia

Front 6

What is the function of calcitonin?

Back 6

Acts to decrease calcium and phosphorus by inhibiting PTH-stimulated bone resorption and renal tubular resorption of calcium and phosphorus

Front 7

What are the 2 locations where Vitamin D is hydroxylated?

Back 7

Hydroxylation to the active form occurs first in the liver, then in the kidney under PTH influence

Front 8

What is the overall effect of metabolically active vitamin D? What are 2 ways vitamin D accomplishes this?

Back 8

Acts to increase serum calcium and phosphorus
1) Increases GI calcium and phosphorus absorption from the gut
2) May facilitate PTH action on bone

Front 9

How much of the total calcium is free ionized calcium? Protein bound?

Back 9

50%-free ionized calcium
45%-protein bound calcium

Front 10

What is the biologically active form of calcium?

Back 10

Free ionized calcium

Front 11

What are the 3 different fractions of calcium?

Back 11

1) Free ionized calcium
2) Protein bound calcium
3) Complexed calcium

Front 12

What fraction of calcium is hormonally regulated?

Back 12

Free ionized calcium

Front 13

What are the effects of hypercalcemia on free ionized calcium? Severe hypocalcemia?

Back 13

Hypercalcemia almost always increases free ionized calcium
Severe hypocalcemia (<6.5) almost always decreases free ionized calcium

Front 14

How does acidosis affect calcium levels?

Back 14

Acidosis increases free ionized calcium, alkalosis decreases it

Front 15

What are protein bound calcium bound to?

Back 15

Anionic proteins (primarily albumin)

Front 16

True or false. Decrease in albumin can decreases total protein.

Back 16

True

Front 17

What is the general cause of hypercalcemia?

Back 17

Results from imbalance of calcium release from bones, excreted by the kidney and absorbed from the GI tract.

Front 18

What is primary hyperparathyroidism?

Back 18

Increased PTH due to neoplasia or idiopathic

Front 19

How can you diagnose primary hyperparathyroidism?

Back 19

Measure PTH levels they will be increased
Increased calcium
Decreased phosphorus

Front 20

What lesions may develop from primary hyperparathyroidism?

Back 20

Soft-tissue mineralization
Bone lesions
Renal failure

Front 21

What is the most common cause of hypercalcemia?

Back 21

Hypercalcemia of malignancy

Front 22

What are 3 tumors that hypercalcemia of malignancy is usually associated with?

Back 22

1) Lymphoma
2) Apocrine adenocarcinomas of the anal sac
3) Multiple myeloma

Front 23

What will you see in blood work in a dog with hypercalcemia of malignancy?

Back 23

Low PTH
High PTHrp (can be measured in dogs)
High calcium levels
Phosphorus=low to normal (can become increased w/ renal disease)

Front 24

What are 5 common causes of hypercalcemia?

Back 24

1) Primary hyperparathyroidism
2) Pseudohyperparathyroidism
3) Renal failure (most common in horses)
4) Hypoadrenocorticism
5) Vitamin D toxicity

Front 25

What is the only cause of hypercalcemia that will have high PTH?

Back 25

Primary hyperparathyroidism

Front 26

What is one of the most common causes of hypercalcemia in equine?

Back 26

Renal failure

Front 27

True or false. Hypercalcemia is common in dogs and cats with renal failure.

Back 27

False, hypocalcemia is more common and hyperphosphatemia

Front 28

What is the most common cause of hypocalcemia?

Back 28

Hypoalbuminemia
-Ionized calcium will be in normal range

Front 29

What are 10 causes of hypocalcemia?

Back 29

1) Hypoalbuminemia
2) Chronic/acute renal failure and renal secondary hyperparathyroidism
3) Pregnancy, parturient, or lactational hypocalcemia
4) rimary hypoparathyroidism
5) Hypomagnesemic tetany
6) Nutritional secondary hyperparathyroidism
7) Uptake of calcium into tissues
8) Precipitation of calcium into calcium oxalate crystals w/ ethylene glycol toxicity
9) Decreased intake
10) Blister beetle toxicity

Front 30

Why does chronic/acute renal failure cause hypocalcemia?

Back 30

Because decreased GFR increases phosphorus resulting in decreased calcium bc of inverse relationship and decreased Vit D activation

Front 31

What is the pathogenesis of secondary renal hyperparathyroidism?

Back 31

Decreased GFR--> increased phosphorus---> decreasd calcium---> increased PTH but there's decreased Vit D activation and decreased responsiveness to PTH so calcium can't increase

Front 32

What is milk fever in cattle?

Back 32

Parturient hypocalcemia in cattle- demand is greater than intake/ability to respond
May also be hypophosphatemic

Front 33

How does hypomagnesemic tetany cause hypocalcemia?

Back 33

Results in decreased PTH activity leading to hypocalcemia

Front 34

What is the pathogenesis of nutritional secondary hyperparathyroidism?

Back 34

Dietary excess of phosphorus (all meat diets) and/or relative or absolute calcium deficiency leads to a low dietary calcium: phosphorus ratio---> increased PTH

Front 35

What are 2 causes of uptake of calcium in to tissues?

Back 35

1) Massive tissue degeneration/ acute tumor lysis
2) Acute pancreatitis

Front 36

What causes blister beetle toxicity?

Back 36

Blister beetles are bailed with hay and ingested by horses
-Also called cantharidiasis in horses

Front 37

How does insulin affect phosphorus levels?

Back 37

Insulin causes phosphorus to shift into the cells

Front 38

What is the most common cause of hyperphosphatemia?

Back 38

Decreased urinary excretion with decreased GFR (except in horses!!!)

Front 39

What are 6 causes of hyperphosphatemia?

Back 39

1) Decreased excretion
2) Hypoparathyroidism
3) Increased intestinal absorption
4) Phosphate release from cells
5) Osteolytic bone lesion
6) Young, growing animal if using ranges for adults

Front 40

What are 5 causes of hypophosphatemia (not that common)?

Back 40

1) Increased urinary loss
2) Decreased intestinal absorption
3) Intracellular phosphate shift
4) Postparturient paresis or eclampsia
5) Equine renal failure w/ hypercalcemia

Front 41

What is grass tetany?

Back 41

Cattle on lush, green pasture with high potassium and low magnesium content-K+ blocks normal magnesium absorption in rumen

Front 42

Why are calves commonly magnesium deficient?

Back 42

Milk is low in magnesium

Front 43

What are 3 causes of hypomagnesemia?

Back 43

1) Decreased intake (most common)
2) Increased loss
3) Hypoproteinemia

Front 44

What are 4 causes of hypermagnesemia?

Back 44

1) Decreased renal excretion
2) Hemolysis
3) Excess oral drugs (such as antacids) w/ Mg2+
4) Milk fever
-Increased PTH may lead to increased renal resorption of Mg2+