Why Citrate and not Phosphate?

[pbnj003]

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Came acrross a question about Ca stones. Question was which one of the following would most likely increase the threshold for crystal precipitation in a solution of Ca Phosphate and Oxalat salts?

Ionized Ca, phosphate concentration, decreased free water, acidification of the urine, saturation of urine, or Citrate.

Citrate was the answer!

I thought that Phosphate would also be able to prevent Ca stones since it binds to free Ca.

Im guessing its because the question is asking about all 3 the best answer would be Citrate?

In the explanation it says increasing the Ca and Phosphate concentrations will increase the precipitation. I can understand why increasing Ca would but not sure about phosphate.

ANyone with an explanation to this?

 

[jfgavina]

yeah, citrate increases the threshold. why? I don't have any idea LOL

 

[norealname]

I am guessing it has something to do with citrate being a weak acid and phosphate being a stronger acid, but I could be wrong.

 

[notarealname]

Ya, also look at the structure of citrate anion, it has 3 negative charges, thus good at grabbing onto calcium, my guess is that it will cause calcium to come together and even precipitate faster, it is also used as an anticoagulant. See wiki: http://en.wikipedia.org/wiki/Citrate