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Yr 4 - ACC > Electrolyte Abnormalities: Calcium & Phosphate > Flashcards

Electrolyte Abnormalities: Calcium & Phosphate Flashcards

1
Q

What is a bone profile?

A

A blood panel that includes:

1) serum calcium

2) serum phosphate

3) serum albumin

4) Alkaline phosphatase (ALP)

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2
Q

Relationship between calcium and albumin?

A

Around 40% of calcium is bound to albumin in the bloodstream, and in this form, it is physiologically inactive

The remaining 60% is known as ionised or ‘free’ calcium, which is physiologically active.

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3
Q

How can hypoalbuminaemia affect calcium?

A

In severe hypoalbuminaemia, the total calcium level may appear normal.

However, ionised (‘free’) calcium levels (which are physiologically active) can be markedly increased due to decreased albumin binding.

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4
Q

How can hyperalbuminaemia affect calcium?

A

If serum albumin levels are raised, the total calcium level may be high, but the serum ionised calcium level may be normal due to increased albumin binding.

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5
Q

What is a ‘corrected’ calcium?

A

Most laboratories report a ‘corrected calcium’ alongside total calcium, in which the serum calcium level is adjusted for the serum albumin level.

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6
Q

3 major roles of calcium?

A

1) bone formation and turnover

2) muscle contraction (including myocardial function)

3) blood coagulation

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7
Q

What are the 3 main processes that determine serum calcium level?

A

1) intestinal absorption

2) renal excretion

3) bone turnover

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8
Q

Where is calcium absorbed?

A

Calcium is absorbed from the small intestine

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9
Q

What is calcium absorption in the small intestine predominantly regulated by?

A

Vitamin D

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10
Q

How does vitamin D deficiency affect calcium?

A

Vitamin D deficiency leads to decreased calcium absorption from the gut.

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11
Q

How do the kidneys regulate calcium excretion?

A

The kidneys regulate the amount of calcium excreted in the urine by altering calcium reabsorption in the distal tubules.

This process is regulated by parathyroid hormone (PTH).

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12
Q

PTH increases calcium levels via what 3 processes?

A

1) Increased PTH leads to decreased levels of renal calcium excretion (i.e. increased calcium levels).

2) Increased PTH levels lead to increased calcium resorption from the bone into the bloodstream.

3) PTH increases vitamin D activation in the kidney (indirectly increases calcium)

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13
Q

What hormone regulates calcium released from bone turnover?

A

PTH

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14
Q

Where are the parathyroid glands found?

A

The parathyroid glands are found just posterior to the thyroid

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15
Q

Role of the parathyroid glands?

A

Act to secrete PTH in response to hypocalcaemia (or low vitamin D).

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16
Q

Define hypercalcaemia

A

> 2.6 mmol/L

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17
Q

Give some causes of hypercalcaemia

A

1) Excessive PTH:
- 1ary hyperparathyroidism
- 3ary hyperparathyroidism
- ectopic PTH secretion (rare)

2) Malignancy:
- myeloma
- bony mets
- paraneoplastic syndromes

3) Excessive Vitamin D:
- exogenous excess
- granulomatous disease (e.g. sarcoidosis)

4) Excess calcium intake:
- ‘milk-alkali’ syndrome

5) Drugs:
- thiazide diuretics
- lithium

6) Hereditary:
- familal hypocalciuric hypercalcaemia

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18
Q

What are over 90% of hypercalcaemia due to? (2 causes)

A

1) Malignancy

2) 1ary hyperparathyroidism

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19
Q

PTH level in hypercalcaemia caused by a) malignancy, b) 1ary hyperparathyroidism

A

a) supressed (due to the negative feedback mechanism)

b) raised

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20
Q

Symptoms of hypercalcaemia?

A

Can be asymptomatic:

  • bones: bone pain, pathological fractures
  • (psych) moans: confusion, hallucination, lethargy, confusion
  • (abdo) groans: abdo pain, vomiting, constipation, pancreatitis
  • (renal) stones: renal colic
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21
Q

Classical ECG finding in hypercalcaemia?

A

Shortened QT interval –> can progress to complete AV nodal block and cardiac arrest.

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22
Q

How does myeloma cause hypercalcaemia?

A

Due primarily to increased osteolastic bone resorption caused by local cytokines (e.g. IL-1, tumour necrosis factor) released by the myeloma cells.

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23
Q

What is the key investigation in patients with hypercalcaemia?

A

PTH levels

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24
Q

How can malignancy cause hypercalcaemia?

A

1) PTHrP from the tumour e.g. squamous cell lung cancer

2) bone mets

3) myeloma: due to increased osteoclastic bone resorption caused by local cytokines

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25
Q

Management of hypercalcaemia?

A

1) Aggressive IV fluid rehydration with normal saline; typically 3-4 litres/day.

2) Following rehydration –> can give bisphosphonates

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26
Q

What can sometimes be used in hypercalcaemia in patients who cannot tolerate aggressive fluid rehydration?

A

Loop diuretics e.g. furosemide

27
Q

Define hypocalcaemia

A

<2.2 mmol/L

28
Q

Give some causes of hypocalcaemia

A

1) PTH deficiency
- 1ary hypoparathyroidism (autoimmune)
- parathyroid damage (post thyroid/parathyroid surgery or post neck irradiation)
- severe hypomagnesaemia (impaired PTH secretion)

2) Vit D deficiency (osteomalacia)

3) Acute pancreatitis

4) Drugs:
- bisphosphonates
- calcitonin

5) CKD

29
Q

Clinical features of hypocalcaemia?

A

1) muscle weakness/cramps

2) muscle tetany/spasm

3) perioral paraesthesia

4) psychological disturbance e.g. depression (if chronic)

5) seizures

30
Q

What are the 2 pathognomonic clinical signs of hypocalcaemia related to muscle tetany?

A

1) Trosseau’s sign

2) Chvostek’s sign

31
Q

What is Chvostek’s sign?

A

Tapping over the facial nerve causes contraction of facial nerves.

32
Q

What is Trosseau’s sign?

A

Occlusion of the brachial artery (e.g. with a BP cuff) leads to involuntary contraction of the hand/wrist (carpal spasm).

Wrist flexion and fingers are drawn together.

33
Q

What may the ECG show in hypocalcaemia?

A

QT prolongation –> can progress to torsades de poines and cardiac arrest.

34
Q

What can give a falsely low calcium level?

A

Contamination of blood samples with EDTA.

35
Q

Management of mild/moderate hypocalcaemia?

A

oral calcium replacement e.g. calcium carbonate

36
Q

Management of severe hypocalcaemia (e.g. carpopedal spasm, tetany, seizures or prolonged QT interval)?

A

IV calcium gluconate (10ml of 10% solution over 10 minutes)

37
Q

Which cells of the parathyroid glands are responsible for the synthesis and secretion of PTH?

A

Chief cells of the parathyroid glands.

38
Q

Via what 3 ways does PTH increase calcium?

A

1) Bone: promotes bone resorption and thus release of calcium into the blood

2) Kidneys: stimulates calcium reabsorption in the distal convoluted tubule

3) Small intestine: indirectly increases absorption of calcium by stimulating 1α-hydroxylase, the enzyme that activates vitamin D in the kidneys

39
Q

How does increased PTH affect phosphate?

A

PTH inhibits phosphate reabsorption, decreasing serum phosphate.

40
Q

What are the 3 types of hyperparathyroidism?

A

1ary, 2ary and 3ary

41
Q

What is the most common type of hyperparathyroidism?

A

1ary

42
Q

What is 1ary hyperparathyroidism driven by?

A

Driven by a pathology of the glands –> one or more of the parathyroid glands is over-secreting PTH despite normal serum calcium, which over time leads to hypercalcaemia.

43
Q

What is the most common cause of 1ary hyperparathyoidism?

A

Adenoma (85%)

44
Q

Give 3 causes of 1ary hyperparathyroidism

A

1) adenoma (85%)

2) hyperplasia (14%, may be associated with other conditions such as multiple endocrine neoplasias)

3) carcinoma (<1%)

45
Q

What is 2ary hyperparathyroidism driven by?

A

A disorder in calcium-phosphate-bone metabolism.

46
Q

What happens in 2ary hyperparathyroidism?

A

In response to low serum calcium levels as a result of another condition, commonly CKD or vitamin D deficiency, the parathyroid glands secrete PTH.

This may or may not normalise serum calcium levels, depending on the underlying condition.

47
Q

What occurs in 3ary hyperparathyroidism?

A

May occur following a prolonged period of 2ary hyperparathyroidism.

In response to chronic PTH secretion, the glands may become hyperplastic and begin to secrete PTH autonomously.

This can lead to hypercalcaemia, especially if the underlying condition impairing calcium metabolism is treated.

48
Q

What history is typically seen in 1ary hyperparathyroidism?

A

Often asymptomatic, may have a family history if associated with a genetic condition like MEN

49
Q

What history is typically seen in 2ary hyperparathyroidism?

A

Conditions affecting calcium metabolism such as vitamin D deficiency, CKD or nutritional calcium deficiency.

50
Q

What history is typically seen in 3ary hyperparathyroidism?

A

As for secondary, often with evidence of recent treatment of the condition such as vitamin D replacement in deficiency.

51
Q

Hormone profile in a) 1ary, b) 2ary and c) 3ary hyperparathyroidism

A

a)
- raised PTH
- raised calcium
- low phosphate

b)
- raised PTH
- low/normal calcium
- raised phosphate
- vit D levels low

c)
- raised PTH
- normal/high calcium
- low/normal phosphate
- vit D normal/low
- raised ALP

52
Q

Do renal stones and bone pain suggest chronic or acute hypercalcaemia?

A

Chronic

53
Q

Management of 1ary hyperparathyroidism?

A

1) surgery: e.g. parathyroidectomy

2) Cinacalcet (in patients with primary hyperparathyroidism in whom surgery would not be appropriate)

54
Q

What is cinacalcet?

A

a calcium-sensing receptor agonist that reduces PTH secretion

55
Q

Complications of 1ary hyperparathyroidism?

A
  • osteoporosis
  • renal impairment & calculi
  • pseudogout
  • pancreatitis
  • CVS disease
56
Q

Causes of hypophosphataemia?

A

1) alcohol excess
2) acute liver failure
3) diabetic ketoacidosis
4) refeeding syndrome
5) primary hyperparathyroidism
6) osteomalacia

57
Q

Complications of hypophosphataemia

A

1) RBC haemolysis

2) WBC and platelet dysfunction

3) muscle weakness and rhabdomyolysis

4) CNS dysfunction

58
Q

Give some causes of a raised ALP

A

1) liver: cholestasis, hepatitis, fatty liver, neoplasia

2) Paget’s

3) osteomalacia

4) bone metastases

5) hyperparathyroidism

6) renal failure

7) physiological: pregnancy, growing children, healing fractures

59
Q

Give 2 causes of a raised ALP and raised calcium?

A

1) bone mets
2) hyperparathyroidism

60
Q

Give 2 causes of a raised ALP and low calcium

A

1) osteomalacia
2) renal failure

61
Q

Give some causes of hypomagnesaemia

A

1) drugs:
- diuretics
- PPIs

2) total parenteral nutrition

3) diarrhoea: acute or chronic

4) alcohol

5) hypokalaemia

6) hypercalcaemia:
- e.g. secondary to hyperparathyroidism
- calcium and magnesium functionally compete for transport in the thick ascending limb of the loop of Henle

62
Q

Features of hypomagnesaemia?

A

Similar to hypocalcaemia:

  • paraesthesia
  • tetany
  • seizures
  • arrhythmias
  • decreased PTH secretion –> hypocalcaemia
  • ECG features similar to those of hypokalaemia
  • exacerbates digoxin toxicity
63
Q
A

Yr 4 - ACC (73 decks)

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