Metabolic bone disease compared
- Topic
A side-by-side table of the common metabolic bone diseases: what is wrong, how the blood tests look and what the biopsy shows.
What it is
Metabolic bone diseases affect the whole skeleton or large parts of it and are told apart by their mechanism, their blood chemistry and, when needed, a bone biopsy. Osteoporosis is too little normal bone; osteomalacia is matrix that will not mineralize; hyperparathyroidism and renal osteodystrophy are disorders of remodelling driven by hormones; Paget disease is chaotic local remodelling. Students are asked to match the laboratory pattern to the disease.
Key facts
- Bone remodelling unit: osteoclasts resorb, then osteoblasts refill; RANKL from osteoblasts drives osteoclasts and OPG blocks it.
- Alkaline phosphatase reflects osteoblast activity; it rises whenever bone formation rises (healing fractures, Paget, osteomalacia, high-turnover bone, growth in children).
- Tetracycline double labelling on biopsy measures how fast osteoid mineralizes; slow mineralization defines osteomalacia.
- Bone densitometry cannot distinguish osteoporosis from osteomalacia: both look 'thin'.
Metabolic bone disease at a glance
| Disease | Main defect | Calcium / phosphate | PTH | Alkaline phosphatase | Biopsy |
|---|---|---|---|---|---|
| Osteoporosis | Too little bone, normally mineralized | Normal / normal | Normal | Normal | Thin, disconnected trabeculae |
| Osteomalacia and rickets (vitamin D lack) | Osteoid does not mineralize | Low or normal / low | High | High | Wide osteoid seams |
| Primary hyperparathyroidism | Excess PTH from the gland | High / low | High | Normal or high | Tunnelling resorption, fibrosis, brown tumours |
| Renal osteodystrophy | CKD: phosphate retention, low calcitriol | Low or normal / high | High | Often high | High or low turnover, osteomalacia |
| Paget disease | Chaotic local remodelling | Normal / normal | Normal | Very high | Mosaic cement lines |
| Osteopetrosis | Osteoclasts do not resorb | Normal / normal | Normal | Normal | Retained calcified cartilage cores |
Clinical notes
- An older woman with a vertebral fracture and normal labs: osteoporosis; with low phosphate and high alkaline phosphatase: think osteomalacia.
- A raised alkaline phosphatase also comes from the liver; GGT or bone-specific alkaline phosphatase tells the source.
Test yourself
Think of the answer, then tap the question to see it.
Which metabolic bone disease has completely normal calcium, phosphate, PTH and alkaline phosphatase?
Osteoporosis (and osteopetrosis).
How do primary hyperparathyroidism and renal osteodystrophy differ in phosphate?
Phosphate is low in primary hyperparathyroidism and high in renal osteodystrophy.
What laboratory finding is typical of Paget disease?
A high alkaline phosphatase with normal calcium and phosphate.
Why can a DXA scan not tell osteoporosis from osteomalacia?
Both lower the measured mineral density; only labs or a biopsy show unmineralized osteoid.
Elsewhere in DurgiPedia
Connections
Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Osteoporosis | MedlinePlus (MedlinePlus, US National Library of Medicine, 2025); Osteomalacia: MedlinePlus Medical Encyclopedia (MedlinePlus, US National Library of Medicine, 2025); Paget's Disease of Bone | MedlinePlus (MedlinePlus, US National Library of Medicine, 2025).
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Representative model, for educational purposes only.