Clinical Calcium Homeostasis

Question 1

How do we calculate free calcium in clinical practice

Answer 1

• Increased albumin decreases free calcium
• Decreased albumin increases free calcium
• Adjust Ca²⁺ by 0.1mmol/L for each 5g/L reduction in albumin from 40g/L

Question 2

What groups are at risk of vitamin D deficiency?

Answer 2

• Infants and children aged < 5 years
• Older people aged > 65 years
• Pregnant and breastfeeding women, particularly
• Individuals with darker skin

Question 3

Descibe the role of parathyroid hormone in maintaining homeostasis

Answer 3

• Parathyroid hormone is key to calcium homeostasis
• In response to a fall in calcium, parathyroid chief cells respond directly by detecting caclium ECG levels via calcium-sensing receptor (CaSR)
• Increased parathyroid hormone is then secreted

Question 4

Apart from maintaining plasma levels of calcium, what else does parathyroid hormone do?

Answer 4

• Promotes reabsorption of calcium from renal tubules and bone
• Mediates the conversion of vitamin D from its inactive form to its active form

Question 5

Symptoms of hypocalcaemia typically develop when adjusted serum calcium levels fall below ____ mmol/L

Answer 5

1.9

(however this threshold does vary and is dependent on the rate of fall)

Question 6

What are some clinical features of hypocalcaemia?

Answer 6

Clinical features: (SPASMODIC)

• Spasms (carpopedal spasm)/Trousseau’s sign (tetany in response to a tightened BP cuff: the wrist and fingers flex and draw together)
• Paresthesia
• Anxiety
• Seizures
• Muscle twitching
• Orientation impaired (time, place and person) and confusion
• Dry skin
• Impetigo herpetiformis
• Chvostek’s sign (the corner of the mouth twitches when the facial nerve is tapped over the parotid)

Question 7

What are the causes of hypocalcaemia due to low parathyroid hormone?

Answer 7

• Genetic disorder
• Autoimmune
• Post-surgical: i.e. thyroidectomy, parathyroidectomy,

Question 8

What are the causes of hypocalcaemia due to high parathyroid hormone?

Answer 8

• Vitamin D deficiency
• Hypomagnesaemia
• Acute pancreatitis
• Acute respiratory alkalosis
• Renal disease

Question 9

State briefly the diagnostic approach to hypocalcaemia

Answer 9

• History
• Examination
• Investigations

Question 10

In the diagnostic appraoch to hypocalcaemia, what do we ask about in the history?

Answer 10

Ask about:

• Symptoms
• Autoimmune disorders
• Neck surgery
• Medication
• Family history
• Calcium and vitamin D intake

Question 11

In the diagnostic appraoch to hypocalcaemia, what do we look for on examination?

Answer 11

Look for:

• Neck scars

Question 12

In the diagnostic appraoch to hypocalcaemia, what investigations do we perform?

Answer 12

• ECG: prolonged QT interval
• Serum calcium
• Albumin
• Phosphate
• PTH
• U+Es
• Vitamin D
• Magnesium

Question 13

Look at this:

Question 14

What is the treatment for “mild” hypocalcaemia (asymptomatic, >1.9mmol/L)

Answer 14

• Oral calcium tablets (with daily plasma calcium levels)
• Vitamin D tablets if deficient
• Stop any precipitating drugs and replace Mg²⁺ if low

Question 15

What is the treatment for “severe” hypocalcaemia (symptomatic, <1.9mmol/L)

Answer 15

• 10-20ml 10% calcium gluconate in 50-100 ml of 5% dextrose IV over 10 minutes with ECG monitoring
• Treat the underlying cause