Changes in Calcium in plasma

[Singh]

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Hello.
Discussed physiologi with a couple of nurses at work yesterday; we analysed a blood-gas test from a patient who had low potassium, low pH, and high ionised calcium. The nurses believed that the increased calcium was due to the low potassium, whereas I said that the low pH increased the calcium in plasma since low pH makes plasma-proteins more +ve and they therefore bind less ca2+. Hence an increase in free ca2+.

Any comments on this folks?

 

[Kalel]

From emedicine.com:

"At a plasma pH of 7.4, each gram of albumin binds 0.8 mg/dL of calcium. This bond is dependent on the carboxyl groups of albumin and is highly dependent on pH. Acute acidemia decreases calcium binding to albumin, whereas alkalemia increases binding, which decreases ionized calcium. Clinical signs and symptoms are observed only with decreases in ionized calcium concentration (normally 4.5-5.5 mg/dL)."

 

[Goofyone]

Yup. H+ ions compete for--and displace--the Ca2+ ions from albumin, so you have higher ionized calcium with low pH even though the total hasn't changed.


Interesting that the K+ was low; high H+ actually falsely raises K+ by displacing it out of cells

 

[souljah1]

agreed,

acidemia can result in hypercalcemia just as alkalemia can result in hypocalcemia (as seen in persistent respiratory alkalosis when many experience a tingling sensation around their lips or in their extremities). changing the plasma pH substantially effects albumin's affinity for cations.