Clinical Calcium Homeostasis Flashcards
What are some dietary sources of calcium?
- Milk, cheese and other dairy foods
- Green leafy vegetables such as broccoli
- Soya beans
- Tofu
- Nuts
- Bread and anything made from fortified flour
- Fish where you eat the bones
What are some functions of calcium?
- Bone formation
- Cell division and growth
- Muscle contraction
- Neurotransmitter release
What percentage of calcium is found where?
98.9% in bones
1% in cells
0.1% in ECF
What are the proportions of plasma calcium concentrations?
- 45% bound (mainly to albumin)
- 10% non-ionised or complexed to citrate
- 45% ionised (biologically important)
What is the normal range of calcium?
2.2 - 2.6mmol/L
How is free calcium calculated?
- Increased albumin decreases free calcium
- Decreased albumin increases free calcium
- Adjust calcium by 0.01mmol/L for each 5g/L reduction in albumin from 40g/L
How does increased albumin impact free calcium levels?
Decreases free calcium
How does decreased albumin impact free calcium levels?
Increases free calcium
When working out free calcium, how is calcium adjusted for reduction in albumin?
Adjust calcium by 0.01mmol/L for each 5g/L reduction in albumin from 40g/L
Does acidosis increase or decrease ionised calcium?
Increases
Since acidosis increases ionised calcium, what does it predispose?
Hypercalcaemia
If Mr Bloggs has calcium of 2.55mmol/L and his albumin is 30g/L, what is his corrected calcium?
- 27mmol/L
- remember the albumin reduction means more calcium is free
- Adjust calcium by 0.01mmol/L for each 5g/L reduction in albuymin from 40g/L
What foods is vitamin D found in?
- Oily fish such as salmon
- Eggs
- Fortified fat spreads
- Fortified breakfast cereals
- Some powdered milks
What are some groups at risk of vitamin D deficiency?
- Pregnancy
- Children
- Elderly
What part of parathyroid glands respond directly to changes in calcium concentrations and secrete parathyroid hormone?
Chief cells
How are alterations in ECF calcium levels transmitted into parathyroid cells?
Via calcium-sensing receptor (CaSR)
How does increases serum calcium impact secretion of parathyroid hormone?
How does decreased serum calcium impact secretion of parathyroid hormone?
What are the effects of parathyroid hormone (PTH)?
- Direct effects that promotes reabsorption of calcium from renal tubules and bones
- Lengthy exposure to inappropriate levels of PTH can lead to osteoporosis
- Mediates the conversion of vitamin D from its inactive to active form
- This conversion takes place in the liver
What does PTH stand for?
Parathyroid hormone
What can lengthy exposure to inappropriate levels of PTH lead to?
Osteoporosis due to the direct effects of PTH that promotes bone reabsorption of calcium from renal tubules and bones
Where does the conversion of vitamin D to its active form take place?
Kidneys
What enzyme is responsible for the conversion of vitamin D to its active form?
When does acute hypocalcaemia occur?
Serum calcium < 2.2mmol/L
What is the clinical presentation of acute hypocalcaemia?
What is the clinical presentation of chronic hypocalcaemia?
What are clinical signs of acute hypocalcaemia?
Trosseau’s sign and Chovstek’s sign
What is the aetiology of hypocalcaemia?
- Disruption of parathyroid gland due to total thyroidectomy
- Following selective parathyroidectomy
- Severe vitamin D deficiency
- Magnesium deficiency
- Cytotoxic drug induced hypocalcaemia
- Pancreatitis
What are the different classifications of hypocalcaemia cause?
Hypoparathyroidism (low PTH)
Secondary hyperthyroidism in reponse to hypocalcaemia (high PTH)
Drugs
What aspects of the history are particularly important for diagnosing hypocalcaemia?
- Symptoms
- Calcium and vitamin D intake
- Neck surgery
- Autoimmune disorders
- Medications
- Family history
What part of the examination is particularly important for diagnosing hypocalcaemia?
Neck scars
What investigations should be done for hypocalcaemia?
- ECG
- Serum calcium
- Albumin
- Phosphate
- PTH
- U and Es
- Vitamin D
- Magnesium
Explain the process of investigations for hypocalcaemia?
1) Confirm hypocalcaemia (adjusted for albumin)
2) Check PTH
- if PTH low or normal, check magnesium
- if PTH high check urea and creatinines
3) If magnesium is low it is magnesium deficiency, if its normal its hypoparathyroidism or calcium sensing receptor defect
4) If urea and creatine is high its renal failure, its its low check vitamin D
5) If vitamin D is low its vitamin D deficiency, if its normal its pseudohypoparathyroidism or calcium deficiency
What are the most common causes of hypocalcaemia?
Vitamin D deficiency
Hypoparathyroidism
What can cause hypoparathyroidism?
- Agenesis
- Such as DiGeorge syndrome
- Destruction
- Neck surgery, autoimmune disease
- Infiltration
- Such as haemochromotosis or Wilson’s disease
- Reduced secretion of PTH (neonatal hypocalcaemia, hypomagnesaemia)
- Resistance to PTH (known as pseudohypoparathyroidism)
- Presents in childhood
- Refers to group of disorders defined by target organ (kidney and bone) unresponsiveness to PTH
- Characterised by hypocalcaemia, hyperphosphatemia and elevated rather than reduced PTH concentrations
- Albright’s hereditary osteodystrophy (AHO): short stature, obesity, shortening of metacarpal bones can occur in these patients
What is agenesis?
Failure of an organ to develop during embryonic growth
What is haemochromotosis?
Condition where iron levels slowly build up in the body, which can damage many organs
What is pseudohypoparathyroidism?
Resistance to PTH
What is pseudoparathyroidism characterised by?
Hypocalcaemia
Hyperphosphatemia
Elevated rather than reduced PTH concentrations
What is a syndrome that that allows agenesis hypoparathyroidism?
DiGeorge syndrome
What can cause hypoparathyroidism due to destruction?
Neck surgery
Autoimmune disease
What can cause hypoparathyroidism due to infiltration?
Haemochromotosis
Wilson’s disease
What can cause hypoparathyroidism due to reduced secretion of PTH?
Neonatal hypocalcaemia
Hypomagnesaemia
What does treatment of hypocalcaemia depend on?
How severe the hypocalcaemia is
When is hypocalcaemia considered to be mild?
Asymptomatic, >1.9mmol/L
When is hypocalcaemia considered to be severe?
Symptomatic, <1.9mmol/L
What is the treatment for mild hypocalcaemia?
- Commence oral calcium tablets
- If post thyroidectomy repeat calcium 24 hours later
- If vitamin D deficient, start vitamin D
- If magnesium low, stop any precipitating drug and replace magnesium
What is the treatment for severe hypocalcaemia?
- Most tablets contain a combination of vitamin D and calcium
- Maintenance dose is about 400-1000 international units
- Higher loading dose required, such as 3200 units daily for 12 weeks
- Vitamin D requires hydroxylation by the kidney to its active form, therefore the hydroxylated derivatives alfacalcidol or calcitriol should be prescribed if patients with severe renal impairment require vitamin D therapy
What is severe hypocalcaemia considered to be?
A medical emergency
What does the Scottish government recommend in relation to vitamin D?
Everyone above the age of 5 should be taking a daily supplement of 10mg vitamin D, particularly during winter months of october to march
