orangeblossom

5+ Year Member
Jan 23, 2011
181
1
bay area
Status
Medical Student
Can somebody explain why ALP levels are increased in osteitis fibrosa cystica?

I thought there would be more osteoclastic activity, hence the subperiosteal thinning, fibrosis etc?
 
OP
orangeblossom

orangeblossom

5+ Year Member
Jan 23, 2011
181
1
bay area
Status
Medical Student
Osteoclasts get activated by osteoblasts. Or at least thats the way I always thought about it.
Gotcha.

Do you know why ALP is normal in hypervitaminosis D? I thought abnormally high vit D levels cause bone resorption, so if osteoclasts are activated, shouldn't ALP be elevated?
 

swollcat

5+ Year Member
Jan 18, 2014
305
101
in osteitis fibrosa cystica. Excess PTH -> osteoblast activation (increase in ALP) -> in order to activate osteoclasts to begin resorbing bone

in hypervitaminosis D, ALP is normal because excess vitamin D = elevated serum Ca++ and phosphate levels (due to more than adequate GI absorption of both ions) -> decrease/no need for PTH -> no osteoblast activation and thus no need to elevate ALP (hence why ALP levels are normal).

This is the point FIRST AID is trying to convey, even though this may be slightly off if one is trying to tell the story one factoid after another.