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Clinical Biochemistry > Calcium and Phosphate Metabolism > Flashcards

Calcium and Phosphate Metabolism Flashcards

1
Q
  1. Bone turnover/remodelling serves as a short term service of calcium and phosphate homeostasis, what is this also in conjunction with?
A
  • Parathyroid hormone (PTH)
  • Vitamin D (1,25-dihydroxy D3)
  • Calcitonin

FGF-23

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2
Q
  1. What % of body calcium is in the bone?

- Where is the remaining %

A

99%

Remaining 1% is mainly intracellular

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3
Q
  1. What percentage and amount of calcium is extracellular

- Is this bound (to albumin) or free?

A

Tiny (<0.1%) extracellular fraction
Plasma extracellular Ca is 2.2-2.6 mmol/L
Around half is free, half is bound

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4
Q
  1. What % of the bodies phosphorus is found in bone?

- What is the remainder of phosphorus?

A

85%

Remainder is mainly intracellular

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5
Q
  1. What levels fluctuate more, calcium and phosphate?
A

Phosphate

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6
Q
  1. What are the clinical features of hypercalcaemia?
A

Depression, fatigue, anorexia, nausea, vomiting,
Abdominal pain, constipation
Renal calcification (kidney stones)
Bone pain
“painful bones, renal stones, abdominal groans, and psychic moans,”

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7
Q
  1. What are some severe clinical features of hypercalcaemia?
A

cardiac arrhythmias, cardiac arrest

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8
Q
  1. What are the most common causes of hypercalcaemia?
A

In ambulatory patients: primary hyperparathyroidism

In hospitalised patients: malignancy

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9
Q
  1. What are the less common causes of hypercalcaemia?
A

Hyperthyroidism

Excessive intake of vitamin D

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10
Q
  1. What is Alkaline phosphatase?
A

. Enzyme found in liver, bone and many other tissues. In presence of bone disease may be elevated due to increased bone turnover.

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11
Q
  1. What should the levels of plasma:
    -Calcium
    -Phosphate
    -Alkaline phosphatase
    -Creatinine
    -PTH
    be in a normal situation (ie the serum biochemistry)
A
  • Serum calcium - modest to marked increase
  • Serum phosphate (decreased reabsorption, increased excretion by PTH) - low or low normal.
  • Serum alkaline phosphatase raised in ~ 20% of cases due to increased bone turnover etc.
  • Serum creatinine may be elevated in longstanding disease (kidney damage)
  • Serum PTH concentration should be interpreted in relation to calcium.
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12
Q
  1. If PTH is inappropriately normal and calcium levels are elevated –> What should you investigate for?
A

PTH inappropriately normal because they should be low if calcium is high
Investigate for hyperparathyroidism

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13
Q
  1. Case study:
    A 52 year old woman was investigated for
    suspected kidney stones.

Serum investigations:

Total calcium	2.82 mmol/L   (2.20 - 2.52)
Phosphate 0.69 mmol/L
(0.75 - 1.50)
Albumin 42 g/L  (35 - 48)
Alkaline phosphatase 135 U/L	 (30 - 100)
PTH	 7.3 pmol/L (1 - 6.9)
Creatinine 118 mol/L (60 - 110)

Explain these results

A

Hypercalcaemia (kidney stones) due to hyperparathyroidism.

Calcium HIGH
(PTH HIGH)
(Creatinine HIGH)

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14
Q
  1. What is the most common cause of hypercalcaemia in hospitalised patients
    (Hypercalcaemia of malignancy)
A

o Humoral, e.g., lung carcinoma secreting PTH related Peptide which acts on PTH receptors.

o Metastatic tumour (release cytokines that promote osteoclast differentiation for bone resorption).

o Haematological: myeloma (tumour originating in the haematopoietic stem cell lineage).

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15
Q

15.What is the most common cause of hypocalcaemia?

A

Vitamin D deficiency Renal failure

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16
Q
  1. What is a less common cause of hypocalcaemia?
A

Hypoparathyroidism

17
Q
  1. What is Rickets?
A

in children, failure of bone mineralisation of cartilaginous growth plates and disordered cartilage formation

18
Q
  1. What is osteomalacia?
A
  • in adults, impaired bone mineralisation of osteoid due to combination of low dietary intake and lack of sunlight exposure.
19
Q
  1. Who is most at risk of osteomalacia?
A

: elderly in nursing homes and not taking supplements or breast-fed babies who are kept out of sunlight.

20
Q
  1. What are some features of osteomalacia?
A

•Diffuse bone pain, waddling gait (way of walking caused by pelvic muscle weakness), muscle weakness, stress fractures (on x-rays).

21
Q
  1. What is the serum biochemistry of osteomalacia?
A

Low/normal calcium, Hypophosphataemia (should increase)

Raised alkaline phosphatase, Secondary hyperparathyroidism

22
Q
  1. What is osteoporosis?
A

health condition that weakens bones, making them fragile and more likely to break

23
Q
  1. What are some features of osteoporosis?
A

oLoss of bone mass: endocrine, malignancy, drug-induced, renal disease, nutritional.
o Loss of bone density
increased fracture risk, increase in bone resorption over formation.

24
Q
  1. Because osteoporosis is usually asymptomatic , how is one usually diagnosed with it?
A

a fragility (minor falls break bones) fracture in wrists/femur or vertebral fractures.

25
Q
  1. What are some endocrine associated causes of osteoporosis?
A
  • Hypogonadism: especially any cause of oestrogen deficiency

* Excess endogenous or exogenous glucocorticoids, Hyperparathyroidism or Hyperthyroidism.

26
Q
  1. What is the difference between a T and Z score?
A

The T-score is a comparison of a person’s bone density with that of a healthy 30-year-old of the same sex.
Its a number (SDs)

The Z-score is a comparison of a person’s bone density with that of an average person of the same age and sex

27
Q
  1. How do we diagnose osteoporosis?
A

Measurement of bone mineral density (BMD)

Dual-energy X-ray absorptiometry (DEXA or DXA scan)

28
Q
  1. In terms of T score, what would be seen in:
    -Normal
    -Osteopenia
    -Osteoporosis
    -Severe Osteoporosis
    ??
A

Normal = T-score of -1 or above

Osteopenia (naturally, with age) = T-score lower than -1 and greater than -2.5

Osteoporosis =T-score of -2.5 or lower

Severe osteoporosis= T-score of -2.5 or lower, and presence of at least one fragility fracture

29
Q
  1. When does bone density peak?
A

•Bone density peaks at 25-30 years old after which it declines, the decline is accelerated by menopause.

30
Q
  1. How is bone mass for men different to bone mass for women
A

higher peak of bone density due to larger mass and no accelerated decline due to no menopause.

31
Q
  1. Does the risk of osteoporosis increase with age?
A

Yes

32
Q
  1. What is the treatment for osteoporosis?
A
  1. Postmenopausal: HRT (hormone replacement therapy) – effects well established but safety of long term treatment has been questioned.
  2. Bisphosphonates e.g. risedronate, alendronate – inhibit function of osteoclasts.
  3. PTH analogues: intermittent dose and time-dependent favour remodelling.
  4. Denosumab – antibody against RANK ligand (reduced osteoclast differentiation so reduced resorption).
  5. Romosozumab (approved 2019, Japan, USA, EU). - antibody against sclerostin protein so increased osteoblast differentiation.
  6. Ensure adequate calcium and vit D intake, appropriate exercise.
33
Q
  1. What is the brief history of HRT?

* I dont know if we need to know this guys:) *

A
    1. US approves Premarin (conjugated equine oestrogen: PREgnant MAre’s urINe) treatment of hot flushes
    1. Feminine Forever by gynaecologist Robert Wilson promoting HRT as lifestyle choice
  • 1970s. Strong association between oestrogen therapy and endometrial cancer so HRT (oestrogen only) use declines.
  • 1980s. Combination HRT products (progestins added to counter proliferative effects of unopposed oestrogen on endometrium) use rises again (oestrogen-progesterone).
  • Preventative effect on BMD, osteoporosis and other claimed benefits: e.g., CV protection – evidence from experimental literature, but no large RCTs (randomised control trials).
  • HRT use peaks late 1990s (15 M women in USA)
34
Q

34 . Which randomised controlled trial took place for HRT?

A

o Women’s Health Initiative (WHI) in USA,, Million Women Study in UK, 2002 preliminary results from WHI published
o No CV protective effects (possibly the reverse).
o Claimed significantly increased breast cancer risk followed by years of controversy and debate

35
Q

35 . What were the Overall Effects from WHI: % of women per year (all ages):

A
  • Fracture risks reduced massively with hormone replacement therapy.
  • Cancer risk reduced with just oestrogen but increased with oestrogen-progesterone combined therapy.
36
Q
  1. What is relative risk versus absolute risk?
A

If something you do triples your risk, then your relative risk increases 300%. Absolute risk is the size of your own risk
(Media quotes only relative risk without absolute risk–> Can be misleading)

37
Q
  1. What were further analysis of the WHI results?

- How were the guidelines for HRT modified because of this

A

• The original WHI participants were older, post-menopausal women (mean age of 64 and 10 years post-menopause).
• Separate analysis of <10 or >10 yrs post-menopause suggested risks were reduced in earlier group.
• Guidelines for HRT modified:
o Short-term therapy (3-5 years) for treating vasomotor (blood pressure) symptoms.
o Lowest effective dose is to be used and long term use is not recommended.

38
Q

38 . What do the NICE guidelines for HRT in 2015 state?

A
  • > HRT is the most effective treatment for relief of vasomotor symptoms although other options, including non-pharmacological ones are available
  • > For most symptomatic. menopausal women, the benefits of HRT outweigh the risks
39
Q
  1. Give an overview of the signal networks in bone remodelling?
A
  • Osteocytes detect small/minor stress fractures and cause osteoclast recruitment, proliferation, differentiation.
  • Activated osteoclasts result in bone resorption (digestion and release of minerals) before they die by apoptosis.
  • Osteoblasts are recruited to the area of resorbed bone and they replace it with osteoid which is then mineralised.

Clinical Biochemistry (7 decks)

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