Hypocalcaemia Flashcards
What are causes of hypocalcaemia?
CKD
Severe vitamin D deficiency
Hypoparathyroidism
Bisphosphonates
Calcitonin
Acute pancreatitis
How does hypoparathyroidism cause hypocalcaemia?
Hypoparathyroidism means less PTH.
Less PTH means less osteoclast activity so less bone resorption so calcium not released.
Less PTH means less reabsorption of Ca in renal tubules so more calcium excreted in urine.
Less PTH means less active vitamin D, so less absorption of calcium from small intestine.
How does CKD cause hypocalcaemia?
Kidneys responsible for conversion of calcidiol to active calcitriol.
Calcitriol involved in enhancing calcium absorption from small intestine.
Impaired renal function means reduced calcitriol so less intestinal calcium absorption.
Also decrease in excretion of phosphate as renal function declines. So elevated phosphate which stimulates parathyroid to release more PTH to activate osteoclasts and increase calcium. However, overtime this eventually leads to bone resorption and hypocalcaemia.
How does severe vitamin D deficiency cause hypocalcaemia?
Vitamin D is essential for the absorption of dietary calcium in small intestine by increasing expression of calcium transport proteins in intestinal lining.
So impaired absorption of intestinal calcium.
Vitamin D also promotes calcium reabsorption in the renal tubules (particularly DCT) so deficiency means more urinary excretion of calcium.
How can bisphosphonates cause hypocalcaemia?
Bisphosphonates inhibit osteoclast activity so less bone resorption and less calcium released into blood stream.
What hormone does the opposite of PTH and inhibits bone resorption but promotes calcium deposition in bones?
Calcitonin
Where is calcitonin made?
C cells of thyroid gland
How does calcitonin cause hypocalcaemia?
Promotes calcium deposition in bones and inhibits calcium resorption by inhibiting osteoclasts.
Calcitonin can also inhibit the reabsorption of calcium in the renal tubules, increasing excretion of calcium.
How can acute pancreatitis cause hypocalcaemia?
Inflammation of pancreas causes pancreatic enzymes to become activated prematurely, including lipases.
Lipases hydrolyse triglycerides in pancreas leading to release of free fatty acids and glycerol.
Calcium released from damaged cells of pancreas react with the fatty acids (saponification) to make calcium salts.
This reduces the concentration of calcium.
How does hypocalcaemia affect an ECG?
Prolonged QT interval
Increases risk of arrhythmia and ventricular fibrillation
What are symptoms of hypocalcaemia?
Muscle cramps and spasms
Paraesthesia (numbness and tingling)
Twitching of facial muscles
Impaired co-ordination and balance
Seizures
Arrhythmias
Dry skin and brittle nails
Confusion
What are 2 signs that can be used to assess hypocalcaemia?
Chvostek’s sign and Trousseau’s sign
What is Chvostek’s sign?
Tapping or lightly stroking facial nerve just in font of ear.
Positive = facial muscle contraction
What is Trousseau’s sign
Inflating blood pressure cuff on arm to pressure higher than systolic blood pressure for a few minutes.
Positive = carpal spasm or flexion of wrist
