Calcium stuff Flashcards
What is hypercalcaemia?
Hypercalcemia refers to a higher than normal calcium levels in the blood, generally over 10.5 mg/dL.
Aetiology of hypercalcaemia
Acidosis: promotes less binding between albumin and calcium. This causes less bound calcium and more free ionised calcium
- osteoclastic bone resorption due to:
- Hyperparathyroidism
- Malignant tumours
Excess vitamin D: increased calcium absorption from GI tract
- Medications
- Thiazide diuretics increases calcium reabsorption in the distal tubule of the kidney
- Lithium
Pathophysiology of hypercalcaemia
With high levels of extracellular calcium, voltage-gated sodium channels are less likely to open up, which makes it harder to reach depolarisation, and makes the neuron less excitable.
Causes:
- slower or absent reflexes
- The sluggish firing of neurons also leads to slower muscle contraction, which causes constipation and generalised muscle weakness.
- In the central nervous system, hypercalcaemia causes confusion, hallucinations, and stupor.
What is hypercalciuria?
Too much calcium in the blood
leads to a loss of excess fluid in the kidneys causing an individual to get dehydrated.
S+S of hypercalcaemia?
- Abdominal pain
- Vomiting
- Constipation
- Dehydration
- Polydipsia
- Polyuria
- Absent reflexes
- Muscle weakness
- Weight loss
- Depression
- Confusion
- Hallucinations
- Stupor
- Hypertension
- Pyrexia
Investigations for Hypercalcaemia?
-
Bloods: high calcium. Also check parathyroid hormone, vitamin D, albumin, phosphorus, and magnesium levels.
- In malignancy, there is low albumin, low chloride, alkalosis, low potassium, high phosphate, high ALP
- Hyperparathyroidism: high PTH
- 24 hr urinary Ca2+ excretion: raised
- Electrocardiogram: tachycardia, AV block, shortening of the QT interval, and sometimes in the precordial leads the appearance of an J wave
Imaging for Hypercalcaemia
- Chest X-ray
- Isotope bone scan
Differential diagnosis for hypercalcaemia
Hyperalbuminaemia (pseudohypocalcaemia): causes there to be a higher concentration of protein-bound calcium, while free ionised calcium concentrations stay the same. This can occur when individuals are dehydrated, concentrating albumin.
Management for hypercalcaemia
- Increase urinary calcium excretion
- Rehydration: increases filtering of Ca2+
- Loop diuretics: inhibit calcium reabsorption in the loop of Henle
- Decrease calcium absorption from GI tract
- Glucocorticoids
- Prevention of bone resorption
- Biphosphonates
- Calcitonin
- Chemotherapy may help in malignancy
Complications of hypercalcaemia
- Kidney stones: due to dehydration combined with hypercalciuria
- Renal failure
- Ectopic calcification e.g. cornea
- Cardiac arrest
What is hypocalcaemia?
Hypocalcemia refers to lower than normal calcium levels in the blood, generally less than 8.5 mg/dL.
Aetiology of hypocalcaemia with increased phosphate
- Chronic kidney disease: lack of reabsorption of Ca2+, lack of active vitamin D
- Hypoparathyroidism: e.g. due to removal of or autoimmune destruction PT glands, DiGeorge syndrome
- Pseudohypoparathyroidism
- Acute rhabdomyolysis: large numbers of cells die and release phosphate. The phosphate binds to the ionised calcium and forms calcium phosphate, making it insoluble and effectively decreasing the total amount in blood.
- Hypomagnesaemia: magnesium is needed for PTH secretion
Aetiology with normal or low phosphate for hypocalcaemia?
- Vitamin D deficiency: leads to less Ca2+ absorption from GI tract
- Osteomalacia
- Acute pancreatitis: free fatty acids end up binding to ionised calcium, which is insoluble and precipitates.
- Over-hydration
- Respiratory alkalosis: high pH (alkalosis) causes more binding between albumin and calcium, which results in less free ionised calcium
Pathophysiology of hypocalcaemia
Low levels of ionised calcium affect a variety of cellular processes e.g.
- With low levels of extracellular calcium, voltage-gated sodium channels are less stable and more likely to open up, which allows the cell to depolarise more easily, and makes the neurone more excitable. This can trigger tetany.
S+S of hypocalcaemia Pneumonic
SPASMODIC
