Hypocalcaemia
Last updated 1st April 2019 - Tom Heaton
This is another really good video from Osmosis on the topic:
https://www.youtube.com/watch?v=KWZrSYo7xuk
https://www.youtube.com/watch?v=KWZrSYo7xuk
Definition
This is defined as an total serum calcium level below the normal range (this will vary between labs, with 2.1-2.6 mmol/L a guide).
A low ionised calcium level may also be defined as this, given that this is the active state.
However, it is important to note that ‘pseudohypocalcemia’ may exist in states of low albumin.
This is because there is less calcium in the blood overall as nearly half is usually bound to albumin.
As it is the free ionised calcium which has the physiological effects, this is not true hypocalcaemia.
There is often a ‘corrected calcium’ level on blood results to take this into account.
A low ionised calcium level may also be defined as this, given that this is the active state.
However, it is important to note that ‘pseudohypocalcemia’ may exist in states of low albumin.
This is because there is less calcium in the blood overall as nearly half is usually bound to albumin.
As it is the free ionised calcium which has the physiological effects, this is not true hypocalcaemia.
There is often a ‘corrected calcium’ level on blood results to take this into account.
Pathophysiology
A good understanding of the normal physiology of calcium is important to understand the pathology. This is discussed elsewhere.
As calcium is such an important ion for many cellular processes, low levels start to lead to a failure of these.
The keys ones involve:
The reduction in levels therefore tends to lead to over excitability of these cells.
This results in the manifestation of tetany, seizures and cardiac conduction abnormalities which form part of the clinical picture.
As calcium is such an important ion for many cellular processes, low levels start to lead to a failure of these.
The keys ones involve:
- Excitable tissue
- Coagulation
The reduction in levels therefore tends to lead to over excitability of these cells.
This results in the manifestation of tetany, seizures and cardiac conduction abnormalities which form part of the clinical picture.
Aetiology
The causes of hypocalcaemia can be thought of as:
- Decreased entry to the blood
- Impaired absorption
- Impaired release
- Impaired absorption
- Increased loss from the blood
- Renal loss
- Redistribution/binding
- Renal loss
Decreased Entry into Blood
This is most commonly due to loss of parathyroid hormone (hypoparathyroidism):
- Surgical removal
- Gland destruction
- Autoimmune
- Radiotherapy
- Metastatic invasion
- Autoimmune
- Congenital disease e.g. DiGeorge’s syndrome
- Hypomagnesaemia
- Dietary deficiency
- Inadequate sunlight
- Malabsorption syndromes
- CKD
- Cirrhosis
- Vitamin D resistance
Increased Removal From Blood
Renal
- CKD
- Diuretics
Redistribution/binding
- Pancreatitis
- Rhabdomyolysis
- Burns
- Tumour lysis
- Massive blood transfusion
- Hyperventilation
Presentation
This may depend of the speed and severity of the decrease.
Rapid changes e.g. with hypoventilation, can produce more notable symptoms.
The history can provide a guide to the possible causes.
The features can be considered on a systems basis.
CNS
CVS
Resp
Rapid changes e.g. with hypoventilation, can produce more notable symptoms.
The history can provide a guide to the possible causes.
The features can be considered on a systems basis.
CNS
- Tetany
- Paraesthesias (especially perioral, and peripherally)
- Muscle cramps
- Seizures
- Chvostek’s sign - tapping of the facial nerve (just below the zygomatic arch) provokes facial twitching
- Trousseau’s sign - inflation of a BP cuff (over SBP) and left for a few minutes triggers spasm in the forearm/hand
CVS
- QT prolongation
- Progression to VT
Resp
- Laryngospasm
- Bronchospasm
Investigations
Bloods
ECG
Urinary calcium - may be persistently high in hypoparathyroidism
- U&Es
- FBC
- LFTs
- Bone profile
- Mg2+
- ABG/VBG - ionised calcium
- PTH/Vitamin D levels
ECG
Urinary calcium - may be persistently high in hypoparathyroidism
Management
This can be differentiated into:
- Replacing calcium
- Correcting cause
Replacing Calcium
Some patients will need IV replacement:
Oral replacement may be suitable in stable patients
- Calcium gluconate 10ml 10% = 2.3 mmol
- Calcium chloride 10ml 10% = 6.8 mmol
- Symptomatic
- Ionised Ca2+ < 0.8 mmol/L
- High CVS support
- Post bypass
- Major transfusion
- Calcium channel blocker overdose
Oral replacement may be suitable in stable patients
Correcting Cause
This may include:
- Correct magnesium
- Stop causative drugs
- Vitamin D - may need activated vitamin D in CKD
Links & References
- Hasudungan, A. Endocrinology - calcium and phosphate regulation. Youtube. 2015. https://www.youtube.com/watch?v=EEM0iRJNhU8
- Hogan, J. Goldfarb, S. Regulation of calcium and phosphate balance. UpToDate. 2018.
- McIndoe, A. Thyroid and parathyroid hormones and calcium homeostasis. e-LFH. 2014.
- Power I, Kam P. Principles of Physiology for the Anaesthetist (2nd ed). 2008. Hodder Arnold.
- Osmosis. Hypocalcemia - causes, symptoms, diagnosis, treatment, pathology. Youtube. 2017. https://www.youtube.com/watch?v=KWZrSYo7xuk
- Tidy, C. Hypocalcaemia. Patient.info. 2015. https://patient.info/doctor/hypocalcaemia
- Nickson, C. Hypocalcaemia. LITFL. 2013. https://lifeinthefastlane.com/ccc/hypocalcaemia/