Chronic renal insufficiency:

1) poor phosphate clearance --> high serum inorganic phosphorous

2) high serum phosphate --> complexes with divalent cation Ca --> Ca falls

3) Ca falls --> triggers PTH axis

4) kidney failure --> decreased activity of 1-hydroxylase at the kidney --> less calcitriol

Since she has celiac spruce --> fat vitamin malabsorption, thus Vit. D is decreased Low vit. D = low calcitriol, low absorption of phosphate from intestine, and low absorption of Ca2+ causing an increase PTH