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Clinical Pathology > Disorders of calcium, phosphate and magnesium. > Flashcards

Disorders of calcium, phosphate and magnesium. Flashcards

1
Q

What is the physiological importance of calcium?

A
  • Muscle contraction
  • Neuronal excitation
  • Enzyme activity (Na/K ATPase, hexokinase etc.)
  • Blood clotting
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2
Q

What is the structural importance of calcium?

A

Key component of hydroxyapatite Ca₁₀(PO₄)₆(OH)₂ - the predominant mineral in bone

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3
Q

What is the physiological importance of phosphate (PO4-)

A
  • The P in ATP – our fuel!
  • Intracellular signalling
  • Cellular metabolic processes e.g. glycolysis
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4
Q

What is the structural importance of phosphate?

A
  • Backbone of DNA
  • Component of hydroxyapatite Ca₁₀(PO₄)₆(OH)₂
  • Membrane phospholipids
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5
Q

What is the physiological importance of magnesium?

A
  • Cofactor for ATP
  • Neuromuscular excitability
  • Enzymatic function
  • Regulates ion channels
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6
Q

What is the normal range for calcium?

A

2.20 -2.60 mmol/L

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7
Q

What are the two key controlling factors for calcium?

A
  • PTH

- Vitamin D and metabolites

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8
Q

What processes is calcium related to/involved in?

A
  • GI uptake
  • Renal Clearance
  • Bone
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9
Q

What is plasma calcium?

A

Total Ca = Ionised Ca + Bound Ca + Complexed Ca

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10
Q

What is ionised calcium?

A

Physiologically active fraction

  • Calcium sensing receptor
  • Cellular Effects
  • Regulation of PTH
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11
Q

What is bound calcium?

A

Bound Calcium

  • Physiologically inactive
  • Albumin main binding protein (~50%)
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12
Q

What is complexed calcium?

A

Salts – calcium phosphate & calcium citrate

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13
Q

What can calcium values be corrected for?

A

Changes in albumin. Better diagnostic performance.

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14
Q

What effect does acidosis have on Ca-albumin?

A

Reduces Ca-albumin

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15
Q

What effect does alkalosis have on Ca-albumin?

A

Increases Ca-albumin

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16
Q

What can alkalosis precipitate?

A

Tetany

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17
Q

What are the endogenous factors related to Vit D absorption?

A
  • Skin colour

- Aging

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18
Q

What are the exogenous factors related to Vit D absorption?

A
  • Ozone
  • Sunscreens & clothing
  • Latitude and season
  • Time of day
  • Diet & supplements
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19
Q

What factors cause vitamin D to fail?

A
  • Age
  • Body fat
  • BMI
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20
Q

What is the role of parathyroid hormone (PTH)?

A

Acts on bone, GI and kidney to increase levels of ionic calcium. Increased ionic Ca acts upon the parathyroid glands to stop the release of PTH.

21
Q

What is the effect of PTH on the kidney?

A

Decreases Ca clearance but increases phosphate excretion.

22
Q

What is the effect of PTH on bone?

A

Increases Ca turnover with net resorption.

23
Q

What is the effect of PTH on the gut?

A

Stimulates the kidney to release vit D.

Vit D increases Ca absorption from the gut.

24
Q

What are the causes of hypocalcaemia?

A
  • Hypoproteinaemia
  • Vit D deficiency
  • Hypoparathyroidism
  • Inadequate intake of Ca
  • Pseudohypoparathyroidism
  • Artefactual causes
25
What are the causes of Vit D deficiency?
- Dietary / Malabsorption - Hepatic disease - Renal Disease - End organ Vitamin D resistance
26
What are the causes of hypoparathyroidism?
- Primary | - Secondary to Mg depletion
27
What is the cause of pseudohyoparathyroidism?
End organ PTH resistance.
28
What are the artefactual causes of hypocalcaemia?
- EDTA contamination | - Venestasis will cause low adjusted calcium (total calcium is unaffected)
29
How can you tell the difference between hypoparathyroidism and Vit D deficiency?
Vit D deficiency - High PTH, low Ca Hypoparathyroidism - rock bottom PTH, low Ca
30
What are the possible causes of hypercalcaemia?
Hyperparathyroidism Malignancy - Lytic lesions - Humoral eg PTHrp Drugs Vitamin D excess - 1a cholecalciferol - Sarcoidosis Bone disease + immobilisation
31
What is the most common cause of ludicrously serum high potassium.
EDTA comtamination
32
What are the differential diagnoses of hypercalcaemia?
- Consider Adjusted Ca: look at the albumin - Check drug history - Exclude excess vitamin D intake - Check for renal failure - Simultaneous measurement of Ca & PTH - Consider rarer causes & more complex investigations
33
How can you tell the difference between hyperparathyroidism and bone metastases?
Hyperparathyroidism - high PTH, high calcium Metastases - low PTH, high calcium
34
What are the causes of phosphate deficiency?
Hyperparathyroidism Excess losses - renal tubular damage - Gastro intestinal - diabetes (diuresis) Poor intake - malnutrition - inadequate IVN ECF / ICF redistribution - like potassium
35
What are the signs/symptoms of phosphate deficiency?
- Haemolysis, thrombocytopenia and poor granulocyte function - Severe muscle weakness, respiratory muscle failure and rhabdomyolysis - Confusion, irritability and coma may be due to a metabolic encephalopathy due to phosphate deficiency - Renal dysfunction
36
What is hypomagnesaemia associated with?
Hypokalaemia Hyponatraemia Hypophosataemia | Hypocalcaemia
37
What are the renal causes of magnesium depletion?
- Diuretic phase of Acute - Tubular Necrosis - Hypercalcaemic states - Drugs - - Antibiotics - gentamicin/carbenicillin - - Chemotherapy - cisplatin - - Diuretics - - FK506
38
What are the GI causes of magnesium depletion?
- Malnutrition - Intravenous nutrition - Diarrhoea - Malabsorption
39
What are the cellular effects of magnesium depletion?
- Reduced mitochondrial respiration & impaired phosphorylation - Defective Na-K ATPase activity - Impaired DNA synthesis
40
What are the biochemical effects of magnesium depletion?
- Hypocalcaemia - Hypophosphataemia - Hypokalaemia
41
What are the endocrine effects of magnesium depletion?
- Impaired PTH release | - PTH resistance in bone
42
What are the cardiovascular effects of magnesium depletion?
- Cardiac irritability | - Reduced contractility
43
What are the CNS effects of magnesium depletion?
- Hyper-reflexia - Tetany - Ataxia / Vertigo - Psychosis / Depression
44
What are the muscle effects of magnesium depletion.
- Weakness - Muscle fibrillation - Myopathic EMG
45
What is the relevance of serum magnesium?
- Poor correlation with Mg status | - Of value acutely
46
What is the relevance of erythrocyte Mg?
- Poor correlation with Mg status | - Affected by high reticulocyte count
47
What is the relevance of leukocyte Mg?
- Good correlation | - Good predictive value
48
What is the relevance of muscle Mg?
- 20% body mass - important physiologically - requires biopsy
49
When should magnesium screening be considered?
With combined hypokalaemia and hypocalcaemia

Clinical Pathology (65 decks)

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