Bone Profile Interpretation Flashcards
What does a bone profile involve?
1) Serum calcium
2) Serum phosphate
3) Serum albumin
4) ALP
What are the 3 main processes that determine serum calcium?
1) Intestinal absorption
2) Renal excretion
3) Bone turnover
Where is calcium absorbed?
Small intestine
What regulates the intestinal absorption of calcium?
Vitamin D
Vitamin D deficiency leads to decreased calcium absorption from the gut.
What regulates the renal excretion of calcium?
PTH
Increased PTH levels lead to decreased levels of renal calcium excretion.
Calcium is released from old bone and taken up by new bone.
What is this process regulated by/
PTH
Increased PTH levels lead to increased calcium resorption from the bone into the bloodstream.
What 3 ways does PTH increase serum calcium?
1) Decreases renal excretion of calcium
2) Increases calcium resorption from bone
3) Indirectly increases calcium levels by increasing Vitamin D activation in the kidney
Give some causes of hypercalcaemia
1) Excessive PTH:
- 1ary hyperparathyroidism
- 3ary hyperparathyroidism
- ectopic PTH secretion (rare)
2) Malignancy:
- myeloma
- bony metastases
- paraneoplastic syndromes
3) Excessive vitamin D:
- exogenous excess
- granulomatous disease (e.g. sarcoidosis)
4) Excessive calcium intake: ‘milk-alkali’ syndrome
5) Renal disease (severe AKI)
6) Drugs:
- thiazide diuretics
- lithium
What 2 drugs can notably cause hypercalcaemia?
1) lithium
2) thiazide diuretics
What are over 90% of cases of hypercalcaemia due to? (2)?
1) 1ary hyperparathyroidism
2) Malignancy
What is the key next step in assessing hypercalcaemia?
Request a PTH
PTH levels in malignancy vs 1ary hyperparathyroidism?
Malignancy –> suppressed due to negative feedback
1ary hyperparathyroidisim –> raised
What are some features of hypercalcaemia?
Bones: bone pain, pathological fractures
Renal stones: renal colic
Abdo groans: abdominal pain, vomiting, constipation, pancreatitis
Psychic moans: confusion, hallucination, lethargy, depression
What will an ECG classically show in hypercalcaemia?
Shortened QT interval –> can progress to cause complete AV nodal block and cardiac arrest.
What does the initial management of hypercalcaemia involve?
Aggressive IV fluid rehydration (saline)
What may be required for treatment of hypercalcemia refractory to rehydration?
Bisphosphonates
Give some causes of hypocalcaemia?
1) PTH deficiency:
- 1ary hypoparathyroidism (autoimmune)
- parathyroid damage (post thyroid/parathyroid surgery or post neck irradiation)
- severe hypomagnesemia (impairs PTH secretion)
2) Vit D deficiency
3) Acute pancreatitis
4) Drugs: bisphosphonates, calcitonin
What 2 drugs can notably cause hypocalcaemia?
1) Bisphosphonates
2) Calcitonin
Features of hypocalcaemia?
- Muscle weakness/cramps
- Muscle tetany/spasm
- Perioral paraesthesia
- Psychological disturbance
- Seizures
What are 2 pathognomonic clinical signs of hypocalcaemia related to muscle tetany?
1) Trosseau’s sign
2) Chvostek’s sign
What is Trosseau’s sign?
Occlusion of the brachial artery (e.g. with a BP cuff) leads to involuntary contraction of the hand/wrist.
What is Chvostek’s sign?
Tapping over the facial nerve causes contraction of facial nerves
What may ECG show in hypocalcaemia?
QT prolongation –> can progress to torsades de pointes and cardiac arrest.
Mx of hypocalcaemia?
Calcium replacement.
Mild/mod symptoms –> oral calcium (e.g. calcium carbonate)
Severe/ECG changes –> IV calcium gluconate
Impact of PTH on phosphate?
Increased PTH causes increases renal excretion of phosphate (i.e. lowers phosphate levels).
What are some causes of hyperphosphataemia?
1) Renal impairment
2) Acute phosphate load:
- tumour lysis syndrome
- rhabdomyolysis
- exogenous phosphate-containing laxatives
3) Excessive phosphate resorption:
- hypoparathyroidism
- drugs (e.g. bisphosphonates)
What is the most common cause of hyperphosphatemia?
CKD –> phosphate excretion markedly impaired as the eGFR falls below 25
Mx of acute hyperphosphatemia?
Acute hyperphosphatemia will generally self-resolve within 6-12 hours if renal function is normal and may need no specific treatment.
IV saline can be used to help accelerate phosphate excretion.
Mx of chronic hyperphosphatemia (e.g. due to CKD)?
Treatment is focused on decreasing phosphate intake (dietary modification) and absorption (phosphate-binding medications).
What are some causes of hypophosphataemia?
1) Decreased absorption:
- inadequate intake
- medications (e.g. antacids or phosphate binders)
- chronic diarrhoea
2) Increased urinary excretion:
- hyperparathyroidism
- vitamin D deficiency
3) Internal redistribution:
- refeeding syndrome (phosphate shifts intracellularly)
- hungry-bone syndrome (increased calcium and phosphate deposition in bone post parathyroidectomy)
3) Renal replacement therapy
Mx of hypophosphataemia?
oral phosphate replacement
What are the 2 key functions of albumin?
1) Maintaining plasma oncotic pressure.
2) Transporting various substances in the bloodstream, such as cations, fatty acids and exogenous drugs.
Give 2 causes of hypoalbuminaemia
1) Decreased albumin production:
- malnutrition
- severe liver disease
2) Increased albumin loss:
- protein-losing enteropathies
- nephrotic syndrome
Raised ALP is often suggestive of what 2 things?
1) Cholestasis
2) Bone disease
What is cholestasis?
an interruption in bile flow from hepatocytes to the gut
How can cholestasis and bone disease (in the context of a raised ALP) be differentiated?
Gamma-glutamyltransferase (GGT)
1) Rise in ALP + normal GGT –> increased bone turnover
2) Rise in ALP + GGT rise –> cholestasis
What are 4 causes of an isolated ALP rise (i.e. normal GGT)?
1) Paget’s disease of the bone
2) Bony metastases
3) Osteomalacia (Vitamin D deficiency)
4) Healing fractures
In what 2 situations is ALP physiologically raised?
1) children & adolescents
2) pregnancy (3rd trimester)
Calcium, phosphate, ALP and PTH levels in 1ary hyperparathyroidism?
Calcium –> raised
Phosphate –> low
ALP –> raised
PTH –> raised
Calcium, phosphate, ALP and PTH levels in bony mets?
Calcium –> raised
Phosphate –> normal
ALP –> raised
PTH –> low
Calcium, phosphate, ALP and PTH levels in Paget’s disease?
Calcium –> normal
Phosphate –> normal
ALP –> raised
PTH –> normal
Note –> Paget’s disease has an ISOLATED rise in ALP.
Calcium, phosphate, ALP and PTH levels in osteoporosis?
All NORMAL
Calcium, phosphate, ALP and PTH levels in osteomalacia?
Calcium –> normal/low
Phosphate –> normal/low
ALP –> raised
PTH –> normal/high
