Biochemical findings in rickets

	Type	Calcium	Phosphorus	Alkaline phosphatase	PTH	25OHD	1,25(OH)₂D	Urine calcium
Calcipenic rickets	Vitamin D-deficient rickets	↓ or N	↓ or N	↑ or ↑↑	↑	↓	↑ or N or ↓	↓ or N
	1-alpha-hydroxylase deficiency*	↓	↓ or N	↑↑	↑	N	↓	↓
	25-hydroxylase deficiency (variable severity)	↓ or N	↓	↑↑	↑	↓	N	↓
	Increased vitamin D catabolism	↓	↓	↑↑	↑	↓	↓	Presumed ↓
	Hereditary resistance to vitamin D^¶	↓	↓ or N	↑↑	↑	N	↑↑	↓
Phosphopenic rickets	X-linked hypophosphatemia (and other FGF23-mediated hypophosphatemic disorders)	N	↓↓	↑	N or slightly ↑	N	N or ↓	↓
	Hereditary hypophosphatemic rickets with hypercalciuria	N	↓ or ↓↓	↑	N or ↓	N	↑	↑
	Nutritional phosphate deprivation	↑ or N	↓ or ↓↓	↑ or ↑↑	↓ or N	N	↑	↑ or N

Calcipenic rickets refers to disorders in which intestinal absorption of calcium is too low to match the calcium demands imposed by bone growth. The term "hypocalcemic" rickets is also used but can be misleading because calcipenic rickets is not always associated with low serum levels of calcium. Among the forms of phosphopenic rickets, nutritional phosphate deprivation can be distinguished by the finding of low urine phosphate (elevated renal TRP), whereas those due to renal phosphate losses usually manifest increased urine phosphate clearance (low TRP).

PTH: parathyroid hormone; 25OHD: 25-hydroxyvitamin D; 1,25(OH)₂D: 1,25-dihydroxyvitamin D; FGF23: fibroblast growth factor 23; TRP: tubular reabsorption of phosphorus; ↑: increased; ↓: decreased; N: normal.
* 1-alpha-hydroxylase deficiency was previously known as vitamin D-dependent rickets type I or pseudo-vitamin D deficiency rickets.
¶ Hereditary resistance to vitamin D was previously known as vitamin D-dependent rickets type II.

Modified with permission from: McMillan JA, DeAngelis CD, Feigin RD, Warshaw JB. Oski's Pediatrics: Principles and Practice, 3rd ed. Lippincott Williams and Wilkins, Philadelphia 1999. p.1619. Copyright © 1999 Lippincott Williams and Wilkins.

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Biochemical findings in rickets