Fibrous Dysplasia -Pathology

Fibrous Dysplasia -Pathology

Question. Describe in detail the serum investigations done in bone disorders and give detailed account of fibrous dysplasia.

Answer. Serum investigations in bone disorders.
Following are the serum investigations done in bone disorders:

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Serum Calcium

• In circulation, the calcium is present in three forms namely ionized calcium (48–50%) protein-bound fraction (40%) and rest as complex calcium.
• The estimated normal value of calcium is around 9 to 10.6 mg/dL and because of diurnal variation it reaches its peak value in mid­day and lowest in early morning.
  It is essential to correct serum calcium values to serum albumin levels as per formula.

Free Serum Calcium

Serum calcium (mg/dL) + [4–serum albumin (g%) × 0.8].
It is advisable to avoid tourniquet while drawing blood for serum calcium estimation irrespective of fasting or non­fasting state.

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Ionized Calcium

• It comprises 48 to 50% of total serum calcium, and is primarily responsible for physiological functions like muscle contraction, coagulation and bone mineralization.
  The normal value of ionized calcium is around 4.5 to 5.2 mg/dL in fasting state (1.l2 to 1.3 micromoles/L) with maximum at 10:00 hours and minimum at 18:00 to 20:00 hours.
• Serum calcium decreases in osteomalacia, hypoparathyroidism, secondary hyperparathyroidism, and increases in primary hyperparathyroidism.

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Serum Phosphate

• Out of total phosphorus in plasma, Inorganic phosphate or phosphorus constitutes 1/3 fraction measurement of which is clinically useful for assessment of metabolic bone disorders.
• The normal range of inorganic phosphate is 2.5–4.5 mg/dL with higher values in elderly male and postmenopausal women.
  The inorganic phosphate is 20% protein bound and rest is free ionic form.
  The serum phosphorus level is higher in infants and children.
  Phosphate is essential to most biological systems.
  High levels are found in renal failure and hypoparathyroidism, while low levels are associated with primary hyperparathyroidism, hypophosphatemic rickets and osteomalacia.

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Serum Magnesium

Magnesium is present mostly in ionized form (55%), protein-bound (30%) and rest in complex form.

The normal value of serum magnesium is 1.7 to 2.6 mg/dL. The hypomagnesemia is observed in hypoparathyroidism.

Increase in serum magnesium level is seen in hemolysis.

Severe and prolonged hypomagnesemia inhibits parathyroid hormone (PTH) release and induces resistance to PTH action on bones.

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Serum 25-hydroxyvitamin D

Vitamin D status is best assessed using serum 25­(OH)D3, as 1,25(OH)D3 has a short half-life and does not accurately reflect true vitamin D status.

Levels are only measured if disorders of vitamin D metabolism are suspected. Whilst rickets and osteomalacia occur with vitamin D deficiency.

The deficiency is suspected at levels below <25 nmol/L (10 mg/mL), and insufficiency is suspected at <75 nmol/L (30 mg/mL).

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Serum Alkaline Phosphatase

The normal value in adults is 40–150 IU/L and in children, 11-306 IU/L. The bone-specific serum alkaline phosphatase (ALP), a marker of osteoblastic activity, is raised in Paget’s disease of bones, metastatic bone disease, osteomalacia, and osteoporosis.

However, it is important to exclude hepatobiliary disease where alkaline phosphatase level is also high, especially in patients with cholestasis.

The bone-specific alkaline phosphatase fraction has better predictive value in evaluating bone disorders.