Ca, Mg, P

Question 1

Name 3 hormones that regulate calcium homeostasis

Answer 1

• Parathyroid hormone PTH ( bone, kidney)
• vitamin D
. Calcitonin (minor) (from thyroid)

Question 2

Name 6 causes hypercalcaemia

Answer 2

• 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

Question 3

Name 5 functions/ consequences of PTH

Answer 3

•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

Question 4

Name 2 effects vit D has on calcium levels

Answer 4

Calcitriol stimulates:
- gut to absorb Ca and P
- bone to stimulate osteoclasts, only in high concetrations

Question 5

Name 3 effects of fibroblast growth factor FGF 23

Answer 5

Secreted by osteocytes when increased calcitriol and P
- hypophosphataemia
-phosphaturia
-decrease serum calcitriol

Question 6

Name 5 causes hyperphosphataemia

Answer 6

• renal insufficiency (common), CKD
• tissue catabolism (common) eg tumour lysis syndrome
• hypoparathyroidism
• vit D intoxication
• acromegaly

Question 7

Why is hyperphosphataemia clinically NB? (2)

Answer 7

• 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

Question 8

Name 3 broad causes and 3 specific causes within each of hypophosphataemia

Answer 8

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

Question 9

Define severe hypophosphataemia and it’s clinical effects (5)

Answer 9

<0,3 mmol/L
- myopathy, muscle weakness, rhabdomyolysis
-haemolysis
- decreased phagocytosis and chemotaxis
-thrombocytopenia

Question 10

Name 2 symptoms of chronic hypophosphataemia

Answer 10

Rickets
Osteomalacia

Question 11

Name 5 causes hypoMg

Answer 11

• 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)

Question 12

Name 5 clinical features and consequences of of hypoMg

Answer 12

-tetany
- agitation, delirium
- ataxia, tremor, choreiform movements, convulsions
- muscle weakness, cardiac arrythmias
- hypocalcaemia (cause and worsen above symptoms)

Question 13

How calculate adjusted plasma calcium?

Answer 13

If albumin <40
Ca + 0,02 x (40- albumin)

If albumin >45
Ca - 0,02 x ( albumin - 45)

Question 14

Name 2 physiological factors that stimulate the kidney to form calcitriol by 1 alpha hydroxylation of 25-oh cholecalciferol

Answer 14

• Increase PTH
• decrease phosphate

Question 15

Name 4 physiological factors that inhibit the kidney to form calcitriol by 1 alpha hydroxylation of 25-oh cholecalciferol

Answer 15

• Decrease PTH
• increase phosphate
• increase fgf-23
• calcitriol production by negative feedback

Question 16

Most common cause primary hyperparathyroid?

Answer 16

Parathyroid adenoma

Question 17

Treatment hyperparathyroid?

Answer 17

Surgery

Question 18

How does malignancy affect calcium

Answer 18

Hypercalcaemia, even if not metastatic ( PTH related peptide secreted)

Question 19

Define primary hyperparathyroidism

Answer 19

Parathyroid glands release too much PTH eg by parathyroid adenoma or hyperplasia
Pth and calcium increased

Question 20

Define secondary hyperparathyroidism and 2 causes

Answer 20

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)

Question 21

Define tertiary hyperparathyroidism and 2 causes

Answer 21

Post renal transplant. Established kidney failure → develop autonomous PTH secretions
Sudden ability to metabolise vitamin D normally → hypercalcaemia.

Question 22

If symptoms hypocalcaemia but calcium is normal, which diagnosis should be considered

Answer 22

Hypomagnesemia

Question 23

What effect does ph have on calcium

Answer 23

Alkalosis = greater binding = free calcium decrease (symptoms hypo Ca)

Acidosis = less binding = free calcium increase

Question 24

Name 9 indications for measuring ionised (free active) calcium

Answer 24

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

Question 25

Approach to hypo Ca ( low total plasma ca) (6)

Answer 25

•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

Question 26

What is relationship between mg and Ca

Answer 26

Directly proportional
(Mg needed to produce pth)

Question 27

Approach to hyper Ca (5)

Answer 27

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)