[7] Hypocalcaemia

Question 1

What is hypocalcaemia?

Answer 1

Low levels of calcium in the blood serum

Question 2

What is the normal range of serum calcium?

Answer 2

2.1-2.5mmolL

Question 3

What is hypocalcaemia defined as?

Answer 3

Less than 2.2mmol/L

Question 4

Where does calcium play a critical role?

Answer 4

In many cellular processes, including;

• Hormone secretion
• Muscle contraction
• Nerve conduction
• Exocytosis
• Activation and inactivation of many enzymes

Question 5

What is calcium homeostasis intimately linked with?

Answer 5

Phosphate homeostasis

Question 6

Why are calcium and phosphate homeostasis intimately linked?

Answer 6

• Because they are both components of hydroxyapatine crystals
• They are both controlled by PTH and calcitonin

Question 7

What are hydroxyapatite crystals?

Answer 7

The major constitutent of the mineral phase of bone

Question 8

Where is most calcium located?

Answer 8

In the bone

Question 9

How much calcium is located in the bone?

Answer 9

Approx 1kg

Question 10

How much calcium is found in the extracellular pool?

Answer 10

About 1g

Question 11

What organs govern calcium homeostasis?

Answer 11

• Intestines
• Bone
• Kidneys

Question 12

What is the typical dietary intake of calcium?

Answer 12

Approx 800mg to 1200mg

Question 13

What are the major dietary source of calcium?

Answer 13

Dairy products

Question 14

How are the intestines involved in calcium metabolism?

Answer 14

• They absorb approx half of the dietary calcium per day
• They secrete calcium for removal from the body

Question 15

What is the net intestinal uptake of calcium?

Answer 15

Approx 175mg/day

Question 16

How are the bones involved in calcium homeostasis?

Answer 16

There is calcium deposition of about 280mg/day, which is matched by an equal amount of calcium reabsorption in the steady state

Question 17

How are the kidneys involved in calcium homeostasis?

Answer 17

They filter about 10x the extracellular pool of calcium per day, but more than 98% is reabsorbed, and the net renal excretion of calcium is about 175mg/day

Question 18

What physiochemical forms does calcium exist in in plasma?

Answer 18

• Free ionised species
• Bound to anionic sites on serum proteins, especially albumin
• Complexed with low-molecular-weight organic anions, e.g. citrate and oxalate

Question 19

What is the total concentration of all 3 forms of calcium found in plasm?

Answer 19

Normally between 2.2 and 2.7mmol/L

Question 20

What % of calcium in the plasma is free?

Answer 20

Approx 45%

Question 21

What % of calcium in the plasma is bound to protein?

Answer 21

45%

Question 22

What % of calcium in the plasma is bound to small organic anions?

Answer 22

10%

Question 23

Why is the ionised form of calcium important?

Answer 23

• It is most important with regards to regulating the secretion of PTH
• It is involved in most of the biologcial actions of calcium

Question 24

What are the causes of hypocalcaemia with increased phosphate?

Answer 24

• Chronic kidney disease
• Hypoparathyroidism
• Pseudohypoparathyroidism
• Acute rhabdomyolysis
• Hypomagnesaemia

Question 25

What are the causes of hypocalcaemia with normal or decreased phosphate?

Answer 25

• Vitamin D deficiency
• Osteomalacia
• Acute pancreatitis
• Overhydration
• Respiratory alkalosis

Question 26

What are the symptoms of mild hypocalcaemia?

Answer 26

• Cramps
• Perioral numbness/parasthesia

Question 27

What are the symptoms of severe hypocalcaemia?

Answer 27

• Carpopedal spasm
• Trousseau’s sign
• Laryngospasm
• Seizures

Question 28

How is mild hypocalcaemia managed?

Answer 28

Giving calcium 5mmol/6h PO, with daily plasma calcium levels

Question 29

What may be required in the management of hypocalcaemia in CKD?

Answer 29

Alfacalcidol

Question 30

How is severe hypocalcaemia treated?

Answer 30

By giving 10mL of 10% calcium gluconate IV over 30 minutes, and repeating as necessary