C - Calcium metabolism Flashcards
Calcium in serum exists in 3 forms - what are they and % of each?
- Free - ionised (50%)
- Albumin bound (40%)
- Complexed (10%) to citrate/phosphate
- Normal Ca range?
- Corrected Ca2+ calculation?
2.2 - 2.6 mM/L
Serum Ca + 0.02(40-serum albumin)
Why is corrected calcium important?
If a patient has low albumin (sepsis), then calcium levels will be measured as low - even if the levels of free (active) calcium are normal.
Corrected Ca is important such that patients with hypercalcemia and a low albumin do not appear to have ‘normal’ calcium levels
PTH - it is released in response to…?
4 roles of PTH?
Released upon low free Ca+ serum
1. GUT - Ca absorption
2. KIDNEY - Ca resorption + Pi excretion
3. stimulates 1-alpha-hydroxylase
4. BONE - Ca resorption by stimulating osteoclasts
what is 1-alpha hydroxylase?
converts 25(OH)D3 into 1,25(OH)2D3 = ACTIVE CALCITRIOL
Where does vitamin D3 activation occur?
Kidney
Another tissue which can release 1-alpha-hydroxylase?
Sarcoid tissue in lung –> hypercalcemia
Roles of Calcitriol?
GUT - Ca and Pi absorption
Causes of Vit D deficiency
Renal failure (low 1-a-hydroxylase)
Anticonvulsants
No sun exposure
Poor diet
Chappatis
4 Features of Rickets
Bowed legs
Costochondral swelling
Widened epiphyses at wrist
Myopathy
4 features of osteomalacia (including biochem)
Losers zones
Increased fracture risk
Low Ca, Pi but HIGH ALP
phosphate levels in:
2ndary HyperPTH from CKD
2ndary hyperPTH from vit D deficiency
PO4 levels are:
high in CKD (inability to secrete it)
low in vit D deficiency (due to PTH being so high)
Familial benign hypercalcemia
-Level of urine Ca
- Level of plasma Ca
- Level of PTH
defect in Ca sensing receptor in parathyroid gland + kidneys
urine Ca low
plasma Ca high
PTH high
pseudohypoparathyroidism
- PTH, Ca and PO4 levels?
PTH resistance
i.e. high levels of PTH, low Ca, high Phosphate
Steps in Vit D activation with locations
Vit D –> 25 hydroxy Vit D (liver)
–> 1,25 hydroxy Vit D (kidney)
3 presentation features of osteoporosis
Pathological fracture
Common in old age
Loss of bone mass
Biochem in osteoporosis?
NORMAL
Ix and threshold for osteoporosis
DEXA scan
< -2.5 T score
Causes of increased bone loss
Sedentary lifestyle
ETOH
Smoking
Low BMI or nutrition
Steroids
Genetics / chronic illness
Tx for osteoporosis
Weight bearing exercise
Vit D / Ca
Bisphosphonates
Teriparatide (PTH derivative)
HRT
In which condition do bones have more protein than Ca?
Osteomalacia
Sx of high Ca
Polyuria/dipsia
Constipation
Confusion / seziures
Cause of high Ca, high PTH
primary hyperPTH
Cause of high Ca, low PTH
cancer
(others = sarcoid, Vit D xs, thryrotoxicosis)
3 causes of cancer with high Ca
Bony mets
Cytokines in myeloma
Small cell lung Ca - PTHrP
Causes of primary hyperPTH
Parathyroid adenoma 80%
Hyperplasia (18%)
Carcinoma (2%)
Sx of primary hyperPTH
bones, stones, moans, groans
Tx for acute high Ca
FLUIDS IV - 4L daily
bisphosphonates if cancer is the cause
Sx of low Ca
Neuromuscular excitability…
Chvosteks
Troussouaes
Hypereflexia
Stridor
Causes of low Ca when high PTH
Low Vit D, CKD, pseudohyperPTH
Causes of low Ca when low PTH
Post thyroidectomy, AI hypoPTH, DiGeorge, low Mg
Features of Pagets (including biochem)
Focal pain
Warm, deformed bones
Fractures
HIGH ALP !!! otherwsie normal biochem
