In Rickets seen –
Serum markers of rickets 

Depending on the type of rickets following changes are seen in serum markers -
	1. Vit I deficiency or calcium deficiency


Vit D enhances absorption of Ca" from gut, So its deficiency results in decreased absorption.
Initially serum Vit D level is maintained because of increased activity of parathyroid gland in response to calcium deficit. After some times, even the compensatory increase in parathormone cannot sustain normal calcium level —>L calcium.
Paratholluone also enhances renal excretion of phosphate Posphaturia -3 serum phosphate.
Because of unavailability of calcium and phosphate, bone mineralization is decrease --> compensatory increase in osteoblastic activity --> Increase alkaline phosphatase.
So, there is

i) Normal to decreased calcium
ii)   Decreased phosphate (except in renal osteodystrophy, where phosphate level is increased because kidney is not able to excrete calcium).
iii) Increased parathormone
iv) Increased alkaline phosphatase 
2. Hypophosphatemic Rickets

This is due to deficiency of phosphate Decreased phosphate.
Calcium level is normal.
As there is no calcium deficiency, there is no compensatory hyperparathyroidism -> Normal paratlzornzone.
Due to unavailability of phosphate, mineralization of bone is decreased and there is increase in compensatory

osteoblastic activity    ->    Alkaline phosphatase
↑ALP
Hypo PO4-2 in blood
Hyperphosphaturia
All of these