Calcium disorders in SA Flashcards
Use a diagram to illustrate calcium homeostasis?
Draw an in depth diagram of how calcium homeostasis is managed in the SA?
What forms of calcium are there in the body?
- total vs. ionised vs. bound vs. complexed
- Standard serum tube gives just a total calcium. The only form that is relevant is the ionised form as this is only bit that will change performance of the cells.
- The bound form tends to be related to albumin. If there are changes in total protein levels our bound level will change.
- Total calcium concentrations are affected by total protein concentrations.
How do we measure ionised calcium?
- Must be correct pH and temp and oxygen free when collected if possible
- Careful with heparin samples as it binds calcium.
- Ionised calcium is very labile so getting an accurate value is very hard. Needs to be in machine very quickly before it clots.
Create a diagram that shows distribution of calcium?
Total calcium measurements include?
- bound (to albumin; ~40%)
- complexes (~10%)
- free/ionised (~50%)
If albumin concentrations decrease, then total calcium decreases because?
Ionised calcium is in equilibrium with the interstitial fluid and is regulated by PTH.
What influences the measured calcium concentration?
If you get a hypercalcemia you didn’t expect probs due to the below:
- Lipaemia
- Haemolysis
- pH
- Albumin concentration
What is the impact of pH on the ionised calcium concentration?
- Alkalosis (not common in dogs, can happen in respiratory disease with hyperventilation) – tends to increase the binding of calcium and therefore tends to cause ionised hypocalcaemia
- Acidosis – tends to reduce the binding of calcium to albumin and therefore tends to cause ionised hypercalaemia
Why is the concentration of (ionised) calcium important in the body?
Action potentials. Things that influence resting and acting potential. Potassium and calcium change the threshold potential. Changes the point at which membrane potential needs to get to before it can fire off. Hypercalcaemia decreases threshold potential: ability to fire and AP has increased.
What are the clinical signs of hypercalcaemia?
- Renal: PU/PD*
- General: Muscle weakness, lethargy, depression, and tremors (neuromuscular)
- Gastrointestinal: Anorexia, vomiting, and constipation
- Cardiac (rare): Arrhythmias secondary to myocardial calcification
*Decreased sensitivity of the renal tubules to ADH and tubular changes secondary to mineralization of the basement membranes, degeneration, and interstitial fibrosis
What are the differentials for hypercalcaemia?
HOGS IN YARDL
Hyperparathyroidism
Ostolytic lesions
Granulomatous disease (monocyttil/ macrophage inflammatory based disease)
Spurious
Idiopathic
Neoplasia
Young
Addison’s
Renal failure
Vitamin (D) toxicity
(Lungworm angistrongylum)
The four major differential diagnoses for hypercalcaemia in the dog are?
- Hypercalcaemia of malignancy*
- most common: lymphosarcoma and anal sac adenocarcinoma. Palpate anal sacs of animal that come in hypercalcaemic and PU/PD.
- Hypoadrenocorticism (Addison’s disease; A)
- Primary hyperparathyroidism (H)
- Chronic kidney disease*
Most common in *
- *HHM – humoral hypercalcaemia of malignancy
How does cancer cause hypercalcaemia?
Note: not all cancers cause hypercalcaemia
By which mechanisms does cancer cause hypercalaemia?
- PTHrP (parathyroid hormone related protein) production (NB low PTH)
- Lymphoma
- Carcinomas
- Vitamin D production (lymphoma)
- Ectopic PTH secretion (humans mainly)
- IL-1 and TGF-b can both stimulate bone resorption
Why do you see hypercalcaemia associated with granulomatous disease?
- Autogenous production of active vitamin D (calcitriol) by macrophages.
- Similar action to 1α-hydroxylase in the kidney.
Show how pattern of phosphate and calcium gives you a strong suspicion of pathological cause?
