Ca, Mg, P Flashcards
Name 3 hormones that regulate calcium homeostasis
• Parathyroid hormone PTH ( bone, kidney)
• vitamin D
. Calcitonin (minor) (from thyroid)
Name 6 causes hypercalcaemia
• Primary hyperparathyroidism: sporadic/familial (common)
• malignancy (common)
- humoral hypercalcaemia of malignancy (pthrp)!
-Widespread skeletal metastases ( commonly breast ca)
- haem malignancy: multiple myeloma, adult T cell leukemia/lymphoma
• Granulomatous disease: sarcoidosis, tb, histoplasmosis, leprosy
• vit D toxicity
• renal transplant: tertiary hyperparathyroidism
• thyrotoxicosis
Name 5 functions/ consequences of PTH
•Phosphaturia (phosphate exchanged for ca )
• Hypercalciuria (due to “overload”)
• mild acidosis (decreased bicarb reabsorption kidney)
• increased plasma calcium (bone release calcium, kidney reabsorb)
• phosphate also reabsorbed from gut with Ca
Name 2 effects vit D has on calcium levels
Calcitriol stimulates:
- gut to absorb Ca and P
- bone to stimulate osteoclasts, only in high concetrations
Name 3 effects of fibroblast growth factor FGF 23
Secreted by osteocytes when increased calcitriol and P
- hypophosphataemia
-phosphaturia
-decrease serum calcitriol
Name 5 causes hyperphosphataemia
- renal insufficiency (common), CKD
- tissue catabolism (common) eg tumour lysis syndrome
- hypoparathyroidism
- vit D intoxication
- acromegaly
Why is hyperphosphataemia clinically NB? (2)
- causes inhibition of 1 alpha hydroxylation of 25 hydroxycholecalciferol in kidneys to Calcitriol (vit D)
- may combine with Ca, causing metastatic calcium deposits in tissues and hypoCa
Name 3 broad causes and 3 specific causes within each of hypophosphataemia
Redistribution
-DKA recovery phase
- enteral/parenteral nutrition with inadequate phosphate; IV glucose
- resp alkalosis
Renal loss
-primary hyperparathyroidism
- renal tubular disease, diuretics
- hypoPhosphataemic rickets, tumour associated osteomalacia (FGF23)
Decrease intake/absorption
-dietary, malabsorption, vomiting
- P binding agents eg Mg, Ca salts
- vit D deficiency
- alcohol withdrawal
Define severe hypophosphataemia and it’s clinical effects (5)
<0,3 mmol/L
- myopathy, muscle weakness, rhabdomyolysis
-haemolysis
- decreased phagocytosis and chemotaxis
-thrombocytopenia
Name 2 symptoms of chronic hypophosphataemia
Rickets
Osteomalacia
Name 5 causes hypoMg
- prolonged diarrhoea, malabsorption most commonly
- refeeding syndrome
- alcoholism - chronic and withdrawal, liver cirrhosis: severe hypoalbuminameia
- PPIs
- renal tubular disease (but in advanced kidney disease, hyperMg)
Name 5 clinical features and consequences of of hypoMg
-tetany
- agitation, delirium
- ataxia, tremor, choreiform movements, convulsions
- muscle weakness, cardiac arrythmias
- hypocalcaemia (cause and worsen above symptoms)
How calculate adjusted plasma calcium?
If albumin <40
Ca + 0,02 x (40- albumin)
If albumin >45
Ca - 0,02 x ( albumin - 45)
Name 2 physiological factors that stimulate the kidney to form calcitriol by 1 alpha hydroxylation of 25-oh cholecalciferol
• Increase PTH
• decrease phosphate
Name 4 physiological factors that inhibit the kidney to form calcitriol by 1 alpha hydroxylation of 25-oh cholecalciferol
• Decrease PTH
• increase phosphate
• increase fgf-23
• calcitriol production by negative feedback
Most common cause primary hyperparathyroid?
Parathyroid adenoma
Treatment hyperparathyroid?
Surgery
How does malignancy affect calcium
Hypercalcaemia, even if not metastatic ( PTH related peptide secreted)
Define primary hyperparathyroidism
Parathyroid glands release too much PTH eg by parathyroid adenoma or hyperplasia
Pth and calcium increased
Define secondary hyperparathyroidism and 2 causes
Due to decreased synthesis calcitriol (need it for ptH to work on bone) → hypocalcaemia → increase PTH as physiolgical response but no increase in calcium
Due to:
• CKD.
• vitamin D deficiency
High PTH (no neg feedback from calcitriol + high P)
High P! (Excr by kidneys impaired)
Normal/low Ca
Low calcitriol (decr synth by kidneys -> low Ca)
Define tertiary hyperparathyroidism and 2 causes
Post renal transplant. Established kidney failure → develop autonomous PTH secretions
Sudden ability to metabolise vitamin D normally → hypercalcaemia.
If symptoms hypocalcaemia but calcium is normal, which diagnosis should be considered
Hypomagnesemia
What effect does ph have on calcium
Alkalosis = greater binding = free calcium decrease (symptoms hypo Ca)
Acidosis = less binding = free calcium increase
Name 9 indications for measuring ionised (free active) calcium
Not routinely done.
• CKD and dialysis
• transplantation
• extra corporeal transfusion
• massive transfusion
• critical illness
• hyper parathyroid
• post op period following parathyroïdectomy
•Severe pancreatitis
• hyper Ca of malignancy
Approach to hypo Ca ( low total plasma ca) (6)
•Plasma albumin and ionized calcium (if hypoalbumin, and or normal ionized/”corrected” calcium, no action needed)
. If ionized calcium low (true hypo ca), do clinical assessment (if positive investigate appropriately)
•If negative, do plasma creatinine (increased = renal impair)
• if normal, do magnesium (low = hypo mg)
.If normal, do plasma PTH
. If PTH low to normal →hypoparathyroid
. If PTH increased, measure phosphate
. If acute high phosphate → hyper p cell lysis; chronic → pseudohypoparathyroid
• if low phosphate, do 25 (oh)d (low =Vit D def)
. If normal/high 25(oh)d, do 1,25 (OH) 2 D
- low: vDDR type 1
- normal/high: osteoblastic metastasis, acute pancreatitis, multiple blood transfusions, inhibitors bone resorption, vDDR type 2
What is relationship between mg and Ca
Directly proportional
(Mg needed to produce pth)
Approach to hyper Ca (5)
Do albumin
- albumin high: do urea
→ high urea = dehydration
→ normal urea = cuffed specimen - albumin normal/low: do phosphate, urea, alkaline phosphatase alp
→ low/normal phosphate+ normal urea = primary/tertiary hyperparathyroid (high pth)
→ high/normal phosphate
> high alp (from increased bone turnover) = bone metastasis (also low chloride,, sarcoidosis, thyrotoxicosis
> normal alp = myeloma (high plasma protein), excess vitamin D, sarcoidosis, milk alkali syndrome if high HCO3 alkalosis)
