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Related Subjects: |Osteoporosis | Calcium & Bone Metabolism |Dual X-ray absorptiometry (DEXA)
Note: Reference sources may vary 📚. Biochemical patterns depend on severity and chronicity of disease, but the table below shows the classic exam-friendly profiles ✅.
Think about the big four markers: Calcium, Phosphate, ALP, and PTH. Vitamin D status helps tie the picture together. 👉 Tip: In exams, look for a signature pattern rather than memorising numbers.
| 🦴 Bone disease | Ca²⁺ | PO₄³⁻ | ALP | PTH | Vit D | 📝 Key Clues |
|---|---|---|---|---|---|---|
| Osteoporosis | Normal | Normal | Normal | Normal | Normal | Structural weakness, not biochemical 🦴.
Diagnosis via DEXA scan. |
| Osteomalacia / Rickets | ↓ | ↓ | ↑ | ↑ / N | ↓ | Soft bones → fractures, Looser’s zones 📉. |
| Paget’s Disease | N | N | ⏫ Markedly ↑ | N | N | Isolated very high ALP 🔑. May have bone pain & deformity. |
| Myeloma | ↑ | N / ↑ | N (↑ if fracture) | N | N | Think CRAB 🦀: ↑Ca, Renal failure, Anaemia, Bone pain. |
| Bone Metastases | ↑ | N / ↑ | ↑ | N | N | Lytic = low ALP, Sclerotic = high ALP.
Prostate → sclerotic ⚙️. |
| Primary Hyperparathyroidism | ↑ | ↓ / N | N / ↑ | ↑ | N | “Stones, bones, groans, moans” 🪨🦴🤯. |
| Secondary Hyperparathyroidism | ↓ | ↑ | ↑ | ↑ | ↓ | Usually CKD or Vit D deficiency. Compensatory high PTH ♻️. |
| Hypoparathyroidism | ↓ | ↑ | N | ↓ | N | Post-thyroidectomy ⚠️. Watch for tetany, Chvostek & Trousseau signs. |
| Renal Osteodystrophy | ↓ / N | ↑ | N / ↑ | ↑ | N / ↓ | Part of CKD-MBD 🧩 (mineral bone disorder). |
| Vitamin D Deficiency | ↓ | ↓ | ↑ | ↑ | ↓ | Classic cause of rickets/osteomalacia ☀️. |
| Vitamin D Resistance (Rickets) | ↓ | ↓ | ↑ | ↑ | N | e.g. X-linked hypophosphataemic rickets 🧬. |
- Osteoporosis: structurally weak bone, biochemistry normal. - Osteomalacia: low Vit D → soft bone, high ALP. - Paget’s: ALP very high in isolation. - Myeloma/Metastases: hypercalcaemia clues, look for CRAB 🦀. - Parathyroid disorders: follow Ca–PO₄ balance (inverse). - Renal failure: phosphate retention, Vit D low, secondary hyperPTH. 👉 In exams: spotting the pattern in labs is the fastest route to the answer.