Nephro - Calcium - Online MedEd Flashcards
Pathophysiology of calcium…
Parathyroid glands behind the thyroid
- Have cells that have packaged parathyroid hormones in vesicles
- There is a calcium sensing receptor, which is inhibitory. If Calcium rises, then calcium turns OFF release of PTH
- Calcium level, PTH released
- PTH is primary way body manages Calcium
What are the effects of PTH?
3 different organ systems
1) Bone - cause resorption of bone (osteoclasts clear bone… release minerals) - elevation of Ca and Phos
2) Kidney - turns on 1,25-vitamin D –> turns on absorption of calcium in gut - resorption of calcium and excretion of phosphorus. There is also creation of vitamin D which goes to the gut
3) Gut (indirect) - activated by 1,25 vitamin D –> absorption of both calcium and phosphorus
* * If kidney is working, kidney always wins = so too much PTH –> calcium elevate, and phosphorus falls!
What is another system that can effect PTH?
1,25 vitamin D secreted from granulomas such as TB/sarcoid –> which can activate the same 3 organ systems
Most calcium is bound to what?
Albumin About 1% is free ionized calcium Normal albumin is 4 Normal calcium is 10 -If albumin changes by 1, then calcium changes by 0.8 in same direction. So Albumin of 3, means calcium of 9.2 -Albumin is typically low
Most calcium disorders can be determined by checking 3 things
Ca
Phos
PTH
Sometimes check vitamin D level
Hypocalcemia - presentation
Tetany
Perioral tingling
Trousseau sign - inflate BP cuff, induce latent tetany
Chvostek’s sign - tap facial nerve, side of face will contract
What should you do if you see hypocalcemia on labs?
Check albumin
- Corrects with albumin
- Not a deficiency of calcium
- Just a product of albumin
If hypocalcemia and albumin does not correct… need to check ionized calcium (this is in the absence of signs of hypocalcemia)
If ionized calcium is low
How to give calcium? IV calcium gluconate/carbonate
Management of hypocalcemia
Give IV calcium (gluconate/carbonate)
Hypercalcemia - presentation
Kidneys stones Psychic moans Abdominal moans Painful bones *Needs treatment!
Don’t have symptoms of hypercalcemia… what to do?
Recheck calcium
If recheck shows elevated calcium, then treat. If normal, then stop
Treatment of hypercalcemia
If asymptomatic –> diagnose
If symptomatic –> needs treatment first
Treatment used to be fluid and lasix. Lasix blocks the paracellular calcium absorption in ascending loop of henle –> calciuria
Loop diuretic/lasix actually has been found to drive the fluid out/drain and cause calcium to be concentrated
**So main treatment of hypercalcemia = VOLUME (lots of fluids). IV fluids!!
Treatment of hypercalcemia - 3 phases
1) Intermediate phase - calcitonin (IV - calcium “tone down”)
2) Long term phase - bisphosphonates (standard)**
3) Indeterminate phase - loop diuretics (only give when volume up)
* So most importantly is fluids and bisphosphonates
So persistent hypercalcemia but no symptoms… differential
1) Hyperparathyroidism
Hyperparathyroidism - 3 categories
1) Primary - autonomous secretion - from a single gland, generally noncancerous
2) Secondary - product of early renal failure, this is an appropriate response to relative hypocalcemia
3) Tertiary - also autonomous (multiple adenomas)
Hyperparathyroidism - presentation
Hypercalcemia
Pathologic fractures - decreased bone density
Brown tumours (not malignancy) that eat away bone
Dx of hyperparathyroidism
Elevated PTH, Elevated Ca, Low Phos
Inappropriate elevation of PTH –> kidney wins, so calcium goes up and phos goes down –> calcium does not turn off PTH
*Do not need vitamin D
Due to autonomous production of PTH from gland
How to differentiate primary, secondary, and tertiary?
Get sestamibi scan
There are 4 parathyroid glands. If primary –> will get 1 gland with adenoma making PTH regardless of Ca. Other parathyroid glands are atrophied/suppressed by elevated Ca
Tertiary hyperparathyroidism –> multiple areas/adenomas that secrete PTH
Tertiary hyperparathyroidism
Chronic low Ca due to inability to make vita D –> up regulate PTH appropriate –> constant stimulation of glands –> multiple areas that secrete PTH
Treatment of hyperparathyroidism
Is surgical resection
And hypoparathyroidism because the other glands have atrophied
Cinacalcet (calcium mimetic agent) is used in CKD to prevent tertiary hyperparathyroidism –> to prevent the amount of PTH made
Hypercalcemia associated with malignancy - pathophys
Cancer can either…
1) Mets - invades bone - causes a release of calcium and phosphorus –> this inhibits PTH release –> so PTH is low (kidney can’t win… no PTH to stimulate the kidney… so Phos will be high as well as calcium)
2) Paraneoplastic syndrome - secrete PTH-related peptide (PTHrP) this is in squamous cell carcinoma of the lungs
Tumour invasion/cancer leads to what values on labs?
Elevated calcium and phos
Low PTH
PTHrP with SCC lungs - what values on labs?
This is PTH So kidney is working and kidney wins Elevated Calcium, Low Phos Natural parathyroid glands are working --> so PTH is LOW -Now measure PTHrP on labs!
Difference between mets and PTHrP on labs
Phosphorus
