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Endocrine System > Calcium Pathophysiology and Clinical Aspects - Hypocalcaemia > Flashcards

Calcium Pathophysiology and Clinical Aspects - Hypocalcaemia Flashcards

1
Q

Name dietary sources of calcium

A
  • Milk, cheese and other dairy foods
  • Green leafy vegetables - broccoli, cabbage and okra
  • Tofu
  • Soya beans
  • Nuts
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2
Q

Name four functions of calcium

A
  • Bone formation
  • Cell division and growth
  • Muscle contraction
  • Neurotransmitter release
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3
Q

Name four different pathways of calcium metabolism?

A
  • Secretion and absorption into gut lumen and excrete via faeces
  • Filtration and reabsorption by the kidneys
  • Absorption and deposition into bone (98% of calcium)
  • Diffusion into and out od cells
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4
Q

How is calcium stored in the bone?

A

Inactive form of calcium

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5
Q

What proportion of calcium is bound in plasma?

A
  • 45% bound (mainly to albumin)
  • 10% non-ionised or complexed to citrate, PO4 et
  • 45% ionised
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6
Q

What is most of the plasma calcium bound to?

A

Albumin

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7
Q

How much calcium is found in the plasma?

A

2.2-2.6mmol/l

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8
Q

How is free calcium calculated?

A
  • Increased albumin decreases free calcium

* Decreased albumin increases free calcium

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9
Q

How does acidosis affect Ca levels?

A

Increased ionised calcium thus predisposing hypercalcaemia

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10
Q

How do you work out corrected calcium?

A

Adjust Ca by 0.1mmol/l for each 5g/l reduction in albumin from 40g/l

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11
Q

Name sources of vitamin D

A

• Mostly from sunlight
• Small number of food:
- Oily fish (salmon, sardine and mackerel)
- Eggs
- Fortified fat spreads and breakfast cereals

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12
Q

Name the different groups at risk of vitamin D deficiency

A
  • Institutionalised patients and prisoners who don’t get outside much
  • Pregnancy requires extra vit D
  • Children
  • Darker skin absorbs less Vit D
  • Clothes covering large proportion of body
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13
Q

How is the release of parathyroid hormone stimulated?

A
  • Parathyroid chief cells secrete PTH
  • Chief cells respond directly changing to Ca concentrations
  • Alterations in ECF Ca levels are transmitted into the parathyroid cells via calcium-sensing receptor (CaSR)
  • PTH is secreted in response to a fall in calcium
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14
Q

What is the relationship between Ca levels and PTH levels?

A

↑ Ca –> ↓ PTH

↓ Ca –> ↑ PTH

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15
Q

What are the actions of parathyroid hormone?

A
  • PTH has direct effects that promote reabsorption of Ca from renal tubules and bone
  • PTH mediates the conversion of vitamin D from its inactive to active form in the kidneys
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16
Q

What bone problem is caused by lengthy exposures to inappropriate levels of PTH?

A

Osteoporosis

17
Q

Describe the step of vitamin D metabolism?

A
  1. Vitamin D from sun or food
  2. Liver produces inactive Vit D
  3. Kidney activates Vit D - this step has input from PTH
  4. Active Vit D helps absorb Ca from the gut
18
Q

What are the boundaries of hypocalcaemia?

A

Serum calcium < 2.2mmol/L

19
Q

What are the clinical features of acute hypocalcaemia?

A
  • Neuromuscular irritability (tetany)
  • Paresthesia
  • Muscle twitching
  • Carpopedal spasm
  • Trosseau’s sign
Cardiac:
• Hypotension 
• HF 
• Papilloedema
• Arrythmia
20
Q

What are the clinical features of chronic hypocalcaemia?

A
  • Parkinsonism
  • Dementia
  • Abnormal dentition
  • Dry skin
21
Q

When do symptoms of hypocalcaemia typically present?

A

Serum calcium falls below 1.9mmol/L

People usually in 2.2mmol/L usually asymptomatic

22
Q

Name different causes of hypocalcaemia

A
  • Hypoparathyroidism - disruption of parathyroid gland due to total thyroidectomy - may be temporary or permanent
  • Selective parathyroidectomy
  • Severe vit D deficiency
  • Mg deficiency
  • Cytotoxic drug-induced hypocalcaemia
  • Pancreatitis, rhabdomyolysis and large vol. blood transfusions
23
Q

What drug causes Mg deficiency?

A

Proton pump inhibitors

24
Q

What are the causes of hypocalcaemia which presents with hypoparathyroidism (low PTH)?

A
  • Genetic disorders
  • Post-surgical (thyroidectomy, parathyroidectomy)
  • Autoimmune
  • Infiltration of gland (iron overload, metastases)
  • Radiation destruction
  • HIV
25
Q

What are the causes of hypocalcaemia which presents with hyperparathyroidism (high PTH)?

A
  • Vit D
  • Pseudohypoparathyroidism
  • Hypomagnesia
  • Renal disease
  • Acute pancreatitis
26
Q

What drugs cause hypocalcaemia?

A
  • Inhibitors of bone resorption (bisphosphonates)

* Cinacalet

27
Q

What do you need to know in the history and examinations of hypocalcaemia?

A 
History:
• Symptoms 
• Ca and Vit D intake 
• Neck surgery 
• Autoimmune disorders (can be autoimmune destruction of parathyroid glands -> hypoparathyroidism)
• Medication 
• FH of hypoparathyroidism

Exam:
• Neck scars

28
Q

What are the investigations used for hypocalcaemia?

A
  • ECG
  • Serum calcium
  • Albumin
  • Phosphate
  • PTH
  • U+Es
  • Vitamin D
  • Magnesium
29
Q

What is the first investigation carried out when hypocalcaemia in confirmed?

A

Check PTH

• Different route of investigations depending on if PTH is high or low

30
Q

What is the investigation route for hypocalcaemia if PTH is low?

A

Check magnesium
• Low –> Mg deficiency
• Normal –> hypoparathyroidism or calcium sensing receptor defect (rare)

31
Q

What is the investigation route for hypocalcaemia if PTH is high?

A 
Check urea and creatinine 
1. High -> renal failure 
2. Normal --> check for Vitamin D 
• Low -> Vit D deficiency 
• Pseudohypoparathyroidism or calcium deficiency
32
Q

What does hypoparathyroidism result from?

A
  • Agenesis (e.g. DiGeorge syndrome)
  • Destruction (neck surgery, autoimmune disease)
  • Infiltration (e.g. haemochromatosis or Wilson’s disease)
  • Reduced secretion of PTH (neonatal hypocalcaemia, hypomagnesaemia)
  • Resistance to PTH
33
Q

What is pseudohypoparathyroidism?

A

Heterogeneous disorders defined by target organ (kidney and bone) unresponsiveness to PTH

Characterised by hypocalcemia, hyperphosphatemia and, in contrast to hypoparathyroidism, elevated rather than reduced PTH concentrations

34
Q

What are the features of pseudohypoparathyroidism?

A

Albright’s heriditary Osteodystrophy (AHO): Obesity, short stature, shortening of the metacarpal bones that can occur in some patients with Pseudohypoparathyroidism

35
Q

What is the treat of hypocalcaemia > 1.9mmol/L but < 2.2mmol/L?

A
  • Commence oral calcium tablets
  • If post thyroidectomy repeat calcium 24 hours later
  • If vit D deficient, start vitamin D
  • If low Mg, stop any precipitating drug and replace Mg
36
Q

What is the treatment of hypocalcaemia < 1.9mmol/L?

A
  • Medical emergency
  • IV calcium gluconate
  • Initial bolus (10% calcium gluconate in 5% dextrose IV over 10mins with ECG monitoring)
  • Calcium gluconate infusion
  • Treat the underlying cause
37
Q

What is given as Vitamin D replacement and when is it required?

A

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

Endocrine System (29 decks)

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