[7] Hypocalcaemia Flashcards
What is hypocalcaemia?
Low levels of calcium in the blood serum
What is the normal range of serum calcium?
2.1-2.5mmolL
What is hypocalcaemia defined as?
Less than 2.2mmol/L
Where does calcium play a critical role?
In many cellular processes, including;
- Hormone secretion
- Muscle contraction
- Nerve conduction
- Exocytosis
- Activation and inactivation of many enzymes
What is calcium homeostasis intimately linked with?
Phosphate homeostasis
Why are calcium and phosphate homeostasis intimately linked?
- Because they are both components of hydroxyapatine crystals
- They are both controlled by PTH and calcitonin
What are hydroxyapatite crystals?
The major constitutent of the mineral phase of bone
Where is most calcium located?
In the bone
How much calcium is located in the bone?
Approx 1kg
How much calcium is found in the extracellular pool?
About 1g
What organs govern calcium homeostasis?
- Intestines
- Bone
- Kidneys
What is the typical dietary intake of calcium?
Approx 800mg to 1200mg
What are the major dietary source of calcium?
Dairy products
How are the intestines involved in calcium metabolism?
- They absorb approx half of the dietary calcium per day
- They secrete calcium for removal from the body
What is the net intestinal uptake of calcium?
Approx 175mg/day
How are the bones involved in calcium homeostasis?
There is calcium deposition of about 280mg/day, which is matched by an equal amount of calcium reabsorption in the steady state
How are the kidneys involved in calcium homeostasis?
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
What physiochemical forms does calcium exist in in plasma?
- Free ionised species
- Bound to anionic sites on serum proteins, especially albumin
- Complexed with low-molecular-weight organic anions, e.g. citrate and oxalate
What is the total concentration of all 3 forms of calcium found in plasm?
Normally between 2.2 and 2.7mmol/L
What % of calcium in the plasma is free?
Approx 45%
What % of calcium in the plasma is bound to protein?
45%
What % of calcium in the plasma is bound to small organic anions?
10%
Why is the ionised form of calcium important?
- It is most important with regards to regulating the secretion of PTH
- It is involved in most of the biologcial actions of calcium
What are the causes of hypocalcaemia with increased phosphate?
- Chronic kidney disease
- Hypoparathyroidism
- Pseudohypoparathyroidism
- Acute rhabdomyolysis
- Hypomagnesaemia
What are the causes of hypocalcaemia with normal or decreased phosphate?
- Vitamin D deficiency
- Osteomalacia
- Acute pancreatitis
- Overhydration
- Respiratory alkalosis
What are the symptoms of mild hypocalcaemia?
- Cramps
- Perioral numbness/parasthesia
What are the symptoms of severe hypocalcaemia?
- Carpopedal spasm
- Trousseau’s sign
- Laryngospasm
- Seizures
How is mild hypocalcaemia managed?
Giving calcium 5mmol/6h PO, with daily plasma calcium levels
What may be required in the management of hypocalcaemia in CKD?
Alfacalcidol
How is severe hypocalcaemia treated?
By giving 10mL of 10% calcium gluconate IV over 30 minutes, and repeating as necessary
