Diagnostic Biochemistry of Calcium and Bone Disorders

Question 1

Calcium Homeostasis

• Leak: TRPV5 and TRPV6 channels (also known as … - intestine and … - kidney, respectively)
• Pump: … calcium ATPase, PMCA1b, … calcium per ATP to ADP
  
  • OR: Basolateral …NA:…CA exhanger, NCX1 extruding calcium (secondarily active mechanism using Na gradient)
• Regulation: 1,25(OH)2D3 and PTH - what do these stand for?

Answer 1

• Leak: TRPV5 and TRPV6 channels (also known as ECaC2 - intestine and ECaC1 - kidney, respectively)
• Pump: Basolateral calcium ATPase, PMCA1b, one calcium per ATP to ADP
  
  • OR: Basolateral 3NA:1CA exhanger NCX1 extruding calcium (secondarily active mechanism using Na gradient)
• Regulation: 1,25(OH)2D3 and PTH - what do these stand for - activated vitamin D and parathyroid hormone

Question 2

• Animal models have demonstrated that ECaC expression is regulated by …
• Gene transcription upregulated by … …. .; phosphorylation of channels and the insertion of ECaC rich vesicles is also available
• 1 alpha hydroxylation of Vit D activated in the kidney by … …

Answer 2

• Animal models have demonstrated that ECaC expression is regulated by 1,25 Vit D (activated Vitamin D)
• Gene transcription upregulated by active vitamin D; phosphorylation of channels and the insertion of ECaC rich vesicles is also available
• 1 alpha hydroxylation of Vit D activated in the kidney by parathyroid hormone

Question 3

Calcium Homeostasis - Sites of exchange/control

• … - Filter v Reabsorption
• … - Absorption v Secretion
• … - Formation v Resorption

Answer 3

• Kidney - Filter v Reabsorption
• GI tract - Absorption v Secretion
• Bone - Formation v Resorption

Question 4

Threats to Calcium Homeostasis

• Disorders of …, … or …
• Disorders of … gland
• Abnormal …. metabolism : intake/synthesis/metabolism

Answer 4

• Disorders of gut, kidney or skeleton
• Disorders of parathyroid gland
• Abnormal vit D metabolism : intake/synthesis/metabolism

Question 5

Parathyroid Hormone

• Secreted as 84aa ‘…’ hormone
  
  • Active moiety
  • Key plasma measurement (not fragments)
• Half life approx … mins
• Low … inhibits release (mimicking ‘hypoparathyroidism’)
• Stimuli to release:
  
  • Fall in plasma ionised … (Acute)
  • Rise in plasma … (Chronic)

Answer 5

• Secreted as 84aa ‘intact’ hormone
  
  • Active moiety
  • Key plasma measurement (not fragments)
• Half life approx 4 mins
• Low magnesium inhibits release (mimicking ‘hypoparathyroidism’)
• Stimuli to release:
  
  • Fall in plasma ionised calcium (Acute)
  • Rise in plasma phosphate (Chronic)

Question 6

Parathyroid Hormone vs PTH related peptide

• Laboratory assay picks up … only, it DOES NOT detect …
• … secreted by a wide variety of tumours, contributes to the humeral hypercalcaemia of malignancy
• … acts as a calciotropic hormone in fetal life and in lactation
  
  • … stimulates the transport of calcium across the placenta
  • … probably contributes to the dramatic but largely reversible bone loss during lactation

Answer 6

• Laboratory assay picks up PTH only, it DOES NOT detect PTHrP
• PTHrP secreted by a wide variety of tumours, contributes to the humeral hypercalcaemia of malignancy
• PTHrP acts as a calciotropic hormone in fetal life and in lactation
  
  • PTHrP stimulates the transport of calcium across the placenta
  • PTHrP probably contributes to the dramatic but largely reversible bone loss during lactation

Question 7

Vitamin D

• D… and D… ( light) sources
• Activation of … via hepatic (25-hydroxylase*) & renal … (1a -hydroxylase) steps
• *constitutive & this is the measurand
• When exposed to … 7-dehydrocholesterol undergoes photochemical … forming vitamin D

Answer 7

• Dietary and Dermal ( light) sources
• Activation of cholecalciferol via hepatic (25-hydroxylase*) & renal hydroxylation (1a -hydroxylase) steps
• *constitutive & this is the measurand
• When exposed to UV light 7-dehydrocholesterol undergoes photochemical cleavage forming vitamin D

Question 8

Vitamin D nomenclature

• Vitamin D2 (Or …) refers to Vitamin D from … sources and Vitamin D3 (or …) from … sources
• Product of first hydroxylation (liver)
  
  • D2 - …-hydroxyvitamin D2 or ercalciferol
  • D3 - …-hydroxyvitamin D3 or calcidiol
• Product of second hydroxylation (kidney)
  
  • 1,25-Dihydroxyvitamin D2 or …
  • 1,25-Dihydroxyvitamin D3 or …

Answer 8

• Vitamin D2 (Or ergocalciferol) refers to Vitamin D from plant sources and Vitamin D3 (or cholecalciferol) from animal sources
• Product of first hydroxylation (liver)
  
  • D2 - 25-hydroxyvitamin D2 or ercalciferol
  • D3 - 25-hydroxyvitamin D3 or calcidiol
• Product of second hydroxylation (kidney)
  
  • 1,25-Dihydroxyvitamin D2 or ercalcitriol
  • 1,25-Dihydroxyvitamin D3 or calcitriol

Question 9

Calcitonin

• Main effect: to reduce bone … (direct and reversible effect on …)
• Role uncertain, thought to protect the skeleton during stressors such as in …
• Main use: tumour marker for medullary … of the …

Answer 9

• Main effect: to reduce bone resorption (direct and reversible effect on osteoclasts)
• Role uncertain, thought to protect the skeleton during stresses (growth and pregnancy)
• Main use: tumour marker for medullary carcinoma of the thyroid

Question 10

FGF-23

• Secreted by osteo…, osteo… and osteo… in response to raised serum …
• Reduces … reabsorption in the renal proximal tubule and inhibits 1-α …
• May be important in renal … disease

Answer 10

• Secreted by osteocytes, osteoblasts and osteoclasts in response to raised serum phosphate
• Reduces phosphate reabsorption in the renal proximal tubule and inhibits 1-α hydroxylase
• May be important in renal bone disease

Question 11

Total Plasma Calcium - Interpretation?

• Total plasma calcium is what is measured in the lab – a … method
• However …% ionised: physiologically active, regulated tightly, measured by blood gas machine
  
  • …% albumin bound
  • … % complexed
• Change in … changes the total calcium (lab method).
• We … therefore and present a range ‘if the albumin were 40 g/L’

Answer 11

• Total plasma calcium is what is measured in the lab – a dye method
• However 50% ionised: physiologically active, regulated tightly, measured by blood gas machine
  
  • 40% albumin bound
  • 10 % complexed
• Change in albumin changes the total calcium (lab method).
• We adjust therefore and present a range ‘if the albumin were 40 g/L’

Question 12

‘Adjustment’ of Plasma Calcium Results

• Method and population specific adjustment to make data fit the range: …-… mmol/L
  
  • Adjusted calcium = calcium +0.02 x (40-albumin)
• Consider 3 patients:
  
  1. Calcium 2.40 Albumin 40 Adjusted Calcium = ?
  2. Calcium 2.16 Albumin 30 Adjusted Calcium = ?
  3. Calcium 2.64 Albumin 50 Adjusted Calcium = ?

Answer 12

• Method and population specific adjustment to make data fit the range: 2.20-2.60 mmol/L
  
  • Adjusted calcium = calcium +0.02 x (40-albumin)
• Consider 3 patients:
  
  1. Calcium 2.40 Albumin 40 Adjusted Calcium = ?
  2. Calcium 2.16 Albumin 30 Adjusted Calcium = ? 2.36
  3. Calcium 2.64 Albumin 50 Adjusted Calcium = ? 2.44

Question 13

Hypercalcaemia + Suppressed PTH

• ?parathyroid cause
  
  • … (E.g. lung, breast or blood)
  • … excess (Activated)
  • Sar…

Answer 13

• Non-parathyroid cause
  
  • Malignancy (E.g. lung, breast or blood)
  • Vit D excess (Activated)
  • Sarcoidosis

Question 14

Hypercalcaemia + Raised (or detectable) PTH

• PTH mediated cause?
  
  • … hyperparathyroidism
  • … hyperparathyroidism
  • … hyperparathyroidism
  • (+ calcium … defects e.g. FHH)

Answer 14

• PTH mediated cause
  
  • Primary hyperparathyroidism
  • Secondary hyperparathyroidism
  • Tertiary hyperparathyroidism
  • (+ calcium receptor defects e.g. FHH)

Question 15

Hypocalcaemia + Increased PTH:

• ?parathyroid cause
• Vit D …, mal…
• … failure
• (PTH … defect e.g. pseudohypoparathyroidism)
• (Vit D … defect)

Answer 15

• Non-parathyroid cause
• Vit D deficiency, malabsorption
• Renal failure
• (PTH receptor defect e.g. pseudohypoparathyroidism)
• (Vit D receptor defect)

Question 16

Hypocalcaemia + Low/normal PTH:

• ?Parathyroid cause
  
  • Such as …
    
    • … e.g. DiGeorge
    • Post … or …
• … deficiency (<0.4 mmol/L)

Answer 16

• Parathyroid cause
• Hypoparathyroidism
• Congenital e.g. DiGeorge
• Post surgery or radiotherapy
• Mg deficiency (<0.4 mmol/L)

Question 17

Normocalcaemic Hyperparathyroidism

• Primary …
  
  • adenoma and hyperplasia
• … deficiency
  
  • sunlight or dietary deficiency or liver disease
• C…
  
  • low 1,25D, high PTH due to hyperphosphataemia, increased PTH fragments
• … illness
  
  • pancreatitis, septicaemia, toxic shock, rhabdomyolysis, ITU admission, adrenal crisis
• M…, / …
  
  • restrictive/exclusion diets, coeliac, chronic pancreatitis
• Drugs
  
  • anti…, bisphoshonates, denosumab, steroids, lithium, PPI, phosphate supplements

Answer 17

• Primary hyperparathyroidism
  
  • adenoma and hyperplasia
• Vit D deficiency
  
  • sunlight or dietary deficiency or liver disease
• CKD
  
  • low 1,25D, high PTH due to hyperphosphataemia, increased PTH fragments
• Acute illness
  
  • pancreatitis, septicaemia, toxic shock, rhabdomyolysis, ITU admission, adrenal crisis
• Malabsorption, dietary
  
  • restrictive/exclusion diets, coeliac, chronic pancreatitis
• Drugs
  
  • anticonvulsants, bisphoshonates, denosumab, steroids, lithium, PPI, phosphate supplements

Question 18

Case 1 - Biochemistry of Calcium and Bone disorders

• Diagnosis?

Answer 18

• Calcium very high - adjusted = 3.24 (for albumin levels 40)
• Phosphate is low
• Creatinine is slightly high - look for teritary parathyroidism? - ruled out not high enough
• PTH is high - driven by this
  
  • Diagnosis = primary hyperparathyroidism

Question 19

Causes of polyuria (5)

Answer 19

Diabetes insipidus, Diabetes Mellitus, CKD, High Ca, Low K

Question 20

Case 2 - Biochemistry of Calcium and Bone disorders

• Diagnosis?

Answer 20

• Calcium high
• Albumin low ish (adjusted calcium = 2.72)
• Creatinine high - kidney injury
• High ALP - hypoparathyroidism?
• Next steps - examine breast / prostate , repeat calcium with PTH, FBC, Elctrophoresis and light chains, PSA, ACE, calcium:creatinine clearance ratio, others: DEXA, skeletal surgery, bone marrow biopsy, h pylori
• Diagnosis - hypercalcaemia confirmed - other tests confirm hyperparathyroidism

Question 21

Case 3 - Biochemistry of Calcium and Bone disorders

• Diagnosis?

Answer 21

• Calcium low
• Albumin low (2.04 adjusted calcium)
• Phosphate high
• ALP high
• Creatinine very very high - renal failure
• PTH very very high - tertiary hyperparathyroidism - very high PTH seen (but secondary because calcium isnt high)
• Diagnosis - secondary hyperparathyroidism (eventually goes to tertiary - calcium back up - hypercalcaemic)

Question 22

Familial Hypocalciuria hypercalcaemia - LoF CaSR

• Uncommon condition where calcium ‘set point’ is higher due to insensitivity of the CaSR .
• Autosomal …, near 100% penetrance, PTH normal or slightly high .
• To exclude FHH, Ca:Cr ratio should be > …
  
  • Formula: Urine Calcium (mmol/l) x [Plasma Creatinine (umol/l) / 1000] DIVIDED BY Plasma Calcium (mmol/l) x Urine Creatinine (mmol/l)
• Condition is …/asymptomatic
• Identical biochemistry to … …
• (Ca 2.6-2.9 – only rarely >3.0)
• Do Not miss as removing parathyroids …
• … will always have been a bit high

Answer 22

• Uncommon condition where calcium ‘set point’ is higher due to insensitivity of the CaSR .
• Autosomal dominant, near 100% penetrance, PTH normal or slightly high .
• To exclude FHH, Ca:Cr ratio should be > 0.01
  
  • Formula: Urine Calcium (mmol/l) x [Plasma Creatinine (umol/l) / 1000] DIVIDED BY Plasma Calcium (mmol/l) x Urine Creatinine (mmol/l)
• Condition is benign/asymptomatic
• Identical biochemistry to primary hyperparathyroidism
• (Ca 2.6-2.9 – only rarely >3.0)
• Do Not miss as removing parathyroids won’t help
• Calcium will always have been a bit high

Question 23

Example of presentation of …

Answer 23

_Example of presentation of FHH (_Familial hypocalciuric hypercalcaemi)

Question 24

Primary hyperparathyroidism is commonest in … people. Unusual in ….

Answer 24

Primary hyperparathyroidism is commonest in older people. Unusual in younger.

Question 25

Calcitonin

• Can help to distinguish C cell … from medullary C cell ….
• There is cross over and therefore ‘pentagastrin-stimulated’ values can be used (more diagnostic).
• However the specific mutations and family history of age of medullary … are used to guide time of prophylactic …

Answer 25

• Can help to distinguish C cell hyperplasia from medullary C cell carcinoma.
• There is cross over and therefore ‘pentagastrin-stimulated’ values can be used (more diagnostic).
• However the specific mutations and family history of age of medullary C cell carcinoma are used to guide time of prophylactic thyroidectomy.

Question 26

Case 4 - Biochemistry of Calcium and Bone Disorders

• Diagnosis?

Answer 26

• Calcium - low
• Albumin normal (no adjustment)
• Phosphate high
• ALP low
• Creatinine normal
• PTH is normal (inappropriate)
  
  • Diagnosis = hypoparathyroidism

Question 27

Case 5 - Biochemistry of Calcium and Bone disorders

• Diagnosis?

Answer 27

• Adjusted calcium - bordeline low
• Phosphate - low
• Alkaline phosphatase - high
  
  • Vitamin deficiency

Question 28

Case 6 - Biochemistry of Calcium and Bone disorders

• Diagnosis?

Answer 28

• Calcium low
• Albumin high (adjusted calcium 1.81)
• Phosphate high
• PTH - quite high
  
  • diagnosis - pseudohypoparathyroidism

Question 29

Pseudohypoparathyrodism - Albright’s Hereditary Osteodystrophy

• The syndrome is associated with a specific clinical … (can be very subtle)
  
  • … stature
  • Shorted 4th +/- 5th … and/or …
  • … faces
  • O…
  • Sometimes .. mental …

Answer 29

• The syndrome is associated with a specific clinical phenotype (can be very subtle)
  
  • Short stature
  • Shorted 4th +/- 5th metacarpals and/or metatarsals
  • Round faces
  • Obesity
  • Sometimes mild mental retardation

Question 30

Psudohypoparathyroidism - or is it…

• It was found that some have the physical … but the … is normal. This is an example of genetic …
  
  • If mutant gene inherited from their mother then manifest pseudo (1a) – … and … features
  • If from father pseudopseudohypoparathyroidism – … features only.
• Predominantly the maternal gene is expressed in the … …

Answer 30

• It was found that some have the physical phenotype but the biochemistry is normal. This is an example of genetic imprinting.
  
  • If mutant gene inherited from their mother then manifest pseudo (1a) – biochemical and physical features
  • If from father pseudopseudohypoparathyroidism – physical features only.
• Predominantly the maternal gene is expressed in the renal tubule

Question 31

Case 6 - Biochemistry of Calcium and Bone disorders

• Diagnosis?

Answer 31

• Alkaline phosphatase really raised
  
  • Could be paget’s disease
  • Used to be common - rarely see it now
  • May be macro ALP

Question 32

Case 7 - Biochemistry of Calcium and Bone disorders

• 67y complains of several months of abdominal pain worse past week plus vomiting 1 to 4 times daily.

Hypertensive Rx Perindopril 4 mg OD, Atorvastatin 10 mg OD and ibuprofen.

Diagnosis?

Answer 32

• Creatinine upper limit of normal
• high calcium
• low potassium
• low magnesium
• low phosphate
• normal PTH
  
  • Gave bisphosphonate to reduce calcium - but then required urgent calcium, potassium, phosphate and magnesium - plus active Vit D - diet issue?
  • Calcium-alkali syndrome - patient used alka-seltzer and milk for dyspepsia - high dose - increasing frequency due to calcium carb for osteoporosis prevention

Question 33

Calcium-Alkali Syndrome

• Triad is…__​

Answer 33

1. Hypercalcaemia
2. Metabolic alkalosis
3. Renal insufficiency

Question 34

The third commonest cause of hypercalcaemia is …

Answer 34

calcium-alkali syndrome

Question 35

Case 8 - Biochemistry of Calcium and Bone disorders

• Diagnosis?

Answer 35

• Calcium high
• Albumin low (Adjusted calcium is 2.83)
• Phosphate high
• ALLP - high
• Creatinine - upper limit of normal
• PTH - low
  
  • likely diagnosis - cancer
  • Actually a sarcoid - not cancer - so why hypercalcaemia?
    
    • granulomas - ACE can be be produced by these - activate vit D - no feedback / not PTH controlled

Question 36

Case 9 - Biochemistry of Calcium and Bone disorders

• Diagnosis?

Answer 36