12.7.2: Calcium disorders Flashcards
Where is most calcium stored in the body?
In the bones
How is calcium obtained?
- Through the diet (or from bone reserves)
- Calcium is absorbed from the gut (or bone) with the help of vitamin D
- Vitamin D is metabolised first in the liver and second in the renal tubules
Which hormone is produced when there is low blood calcium? What effect does it have?
- Parathyroid hormone (PTH) is produced from the parathyroid glands
- This leads to decreased Ca clearance and increased calcitriol production from the kidneys
- There is also increased turnover/ release of Ca from bone
- There is also increased Ca absorption from the gut
PTH
What is another name for 1,25-DHCC?
Calcitriol
What are the 3 forms of calcium that exist in circulation? Which one is monitored by the parathyroid glands?
- Ionised calcium (most) - monitored by parathyroid glands
- Bound calcium
- Complexed calcium (least)
What effect might low albumin have on the bound calcium fraction?
- Albumin = the protein that calcium is bound to in the blood
- Hypoalbuminaemia = reduced bound calcium
If you contaminate your sample with ……….. , it will bind to calcium and produce a falsely low result.
EDTA
Explain how the animal could by physiologically low on calcium even though the total calcium is high.
- Elevated phosphate (e.g. with renal disease) increases the complexed fraction (it steals calcium from the ionised fraction)
- Therefore total calcium could be high but physiologically the animal is low
Which fraction of calcium is it best to test?
Ionised calcium
When calcium increases, it will complex with phosphate in the blood. Where else will this happen?
In the tissues
We see this because this tissue mineralisation stops kidneys, gastric mucosa etc. from working.
What are the differentials for hypercalcaemia and how will you remember?
HOGS IN YARD
* Hyperparathyroidism
* Osteolysis
* Granulomatous disease
* Spurious (e.g. affected by albumin)
* Idiopathic
* Neoplasia
* Young
* Addison’s disease
* Renal disease (total Ca, horses)
* Vitamin D toxicity
What are some differentials for total hypercalcaemia in dogs?
What are some differentials for total hypercalcaemia in cats?
Explain how granulomatous disease can lead to hypercalcaemia
- Macrophages have the ability to do the final oxidation step for Vitamin D
- More Vitamin D -> more calcium absorbed
Differentials for parathyroid-dependent hypercalcaemia
Differential for parathyroid-independent hypercalcaemia
What do we need to be mindful of after removing a parathyroid adenoma?
- Parathyroid adenoma will have been producing too much PTH leading to hypercalcaemia
- Negative feedback means the other parathyroid glands will have shrunk
- When we remove the tumour the animal with become hypocalcaemic
- Aim for subclinical hypoCa -> we want the parathyroid glands to react, but not so badly that the challenge kills the animal
Clinical signs of hypocalcaemia
- Twitching
- Collapse
- Seizures
Explain why each of the following clinical signs could occur in a hypercalcaemic animal
1
2
3
4
Treatment of hypercalcaemia
- Diuretic increases renal flow rate which means it is harder for calcium to be picked up
- Bisphosphates are osteoclasts poisons -> stop calcium being taken out of bone
- Glucocorticoids make neoplastic lymphocytes disappear for a while -> if you don’t have a diagnosis yet, be careful what you treat with!
Pathogenesis and clinical findings with secondary renal hyperparathyroidism
Acute therapy for hypocalcaemia
Long-term therapy for hypocalcaemia
Differentials for hypocalcaemia
