Stages of vitamin D deficiency rickets

Stage	Serum calcium (Ca)	Serum inorganic phosphorus (Pi)	Parathyroid hormone (PTH)	Mechanisms	Radiologic and clinical findings of rickets
1	Low or normal	Normal	Normal or elevated	Vitamin D deficiency causes impaired intestinal absorption of calcium	None, or osteopenia only
2	Normal	Low	Elevated	Elevated PTH mobilizes calcium from bone, retains calcium at the kidney, and promotes production of 1,25(OH)₂D	Clinically apparent rickets (radiographic and/or physical findings in the skeleton)
3	Low	Low	Very elevated	Serum calcium falls as hyperparathyroidism is unable to compensate for impaired intestinal calcium absorption. Hyperparathyroidism may also lead to aminoaciduria and hyperphosphaturia.*	Severe radiographic and physical signs of rickets

1,25(OH)₂D: 1,25 dihdroxyvitamin D.
* Urinary phosphate is inappropriately high relative to the low levels of phosphate in the blood (ie, the renal clearance of phosphate is elevated), but actual concentrations of phosphate in the urine may not be elevated.

Graphic 86780 Version 4.0

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Stages of vitamin D deficiency rickets