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SBCP Biochemistry > Calcium, Magnesium and Phosphate > Flashcards

Calcium, Magnesium and Phosphate Flashcards

1
Q

What percentage of Ca is found in skeleton?

A

99%

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2
Q

How much serum Ca is bound to plasma proteins

A

50%

Remainder is Ionised Ca

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3
Q

How is calcium measurement linked to proteins?

A

Falls and rises with protein

Therefor take blood sample without tourniquet as this will increase the protein content

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4
Q

How is calcium level adjusted for protein content? (recognise equation)

A

Increase Ca by 0.02 mmol for every 1 g fall in albumin below 40g/L

(Decreased by 0.02 for every 1 g when albumin is ABOVE 40g/L)

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5
Q

How does PTH increase calcium?

A

Increased bone resorption
Increased gut resorption
Increased renal absorption
Increased activated D synthesis

EXCRETES MORE PHOSPHATE

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6
Q

Summarise Vit D metabolism

A

UV light converts cholesterol to vit D

Converted in liver to 25 Vit D in liver

Converted to activated 1,25 vit D in kidneys

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7
Q

Drug causes of hypercalcaemia

A

Thiazides

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8
Q

Endocrine causes of hypercalcaemia

A

PTH excess
Hyperthyroidism
Addisons
Familial hypocalciuric hypercalcaemia

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9
Q

Investigation of hypercalcaemia?

A

Take UNCUFFED, FASTING sample

Look at phosphate lvl (will be low)

ALP for bone disease

PTH and Vit D levels

CXR for sarcoid

Plasma protein electrophoresis (myeloma)

Urine calcium

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10
Q

Management of hypercalcaemia?

A 
Rehydration (4-6 L in 24 hours)
Monitor urine output
Loop diuretic
Monitor K+
Bisphosphonates to bind Ca
Hydrocortisone for myeloma or sarcoid
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11
Q

Causes of Hypocalcaemia

A 
Lack of Vit D
Renal failure (increased phosphate)

Vit D deficiency

BISPHOSPHONATES

Hypoparathyroidism

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12
Q

Clinical features of hypocalcaemia

A

Tetany
Chvosteks sign
Trousseaus sign
Prolonged QT interval

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13
Q

Management of (1) mild and (2) severe hypocalcaemia

A

Mild: oral calcium, vit D

Severe: IV calcium gluconate

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14
Q

Where is phosphate sotred in body?

A

85% in bone, mainly intracellular

Required for ATP, and DNA

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15
Q

Causes of hypophosphatemaia?

A 
Decreased intake
Decreased absorption(low vit D

Shift into cells:
RESPIRATORY ALKALOSIS
INSULIN

Increased urinary excretion:
HYPERPARATHYROIDISM
Renal tubular defects

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16
Q

What condition is hypophosphataemia most often linked to?

A

REFEEDING SYNDROME

Lots of glucose causes phosphate to quickly shift into the cells

Causes respiratory alkalosis

Also linked to alcohol abuse

17
Q

Adverse affects of hypophosphataemia eg in refeeding syndrome?

A

Rhabdomyolysis
Cardiomyopathy
ARDS
Erythrocyte and WC dysfunction

18
Q

Treatment of hypophosphataemia?

A

MILK/oral supplements

IV over 12 hours

EXCESS PHOSPHATE CAN CAUSE HYPOCALCAEMIA!!

19
Q

When is hyperphosphataemia seen? (1)

A

Renal failure

20
Q

Where is magnesium stored?

A

67% in bones
30% in cells

When dietary Mg is low, the loops of Henle are v efficient at retaining Mg

21
Q

Causes of hypomagnaesia?

A

Poor intake or malabsorption
Diarrhoea
REFEEDING SYNDROME
Alcohol withdrawal

22
Q

Features of hypomagnesia

A

Same as hypocalcaemia

23
Q

Treatment of hypomagnesia? (just recognise)

A

Oral or IV Mg

30mmol in first 24 hrs and the 20mmol per 24 hours

24
Q

Causes of raised ALP?

A

Childhood, pregnancy

Bone damage or malignancy

Liver disease

25
Q

Which bone disease? Normal Ca, Po4 and ALP

A

Osteoporosis

26
Q

Which bone disease? Low Ca and phosphate, increased ALP, low vit D

A

Osteomalacia due to defective bone mineralisation

27
Q

Which bone disease? Increased ALP ++, normal Ca and phosphate

A

Paget’s, increased bone remodelling

28
Q

Which bone disease? Increased Ca and ALP, PO4 normal or raised

A

?Bone metastases

29
Q

Which bone disease? Raised calcium, normal phosphate, ALP NORMAL

A

Myeloma

30
Q

Bone biochemistry in primary hyperparathyroidism

A

High Ca
Low phosphate
Normal ALP

SBCP Biochemistry (9 decks)

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