Pam,

Thank you for your response in the below post. This is what you posted:

If a person has a high pH (>7.45) with a low CO2 and a high HCO3, they have a primary metabolic alkalosis with respiratory compensation. If they have a low pH (< 7.35) with a high CO2, and a low HCO3, they have a primary respiratory acidosis with metabolic compensation. CO2 is acid and HCO3 is base or alkaline.

Now my question. The equation from a link on measuring anion gaps posed this equation.

Na - (Cl + HCO3) = anion gap

None of my tests showed bicarbonate (HCO3) results, so I worked my result out by using what I did know; (Na, Cl, and anion gap). This, I thought, gave me the answer to what my HCO3 levels were, but this number also matched exactly to my results of CO2 levels on every test. So, do I need to get a separate testing to know what my HCO3 levels really are, seeing as the hospital seems to be using my CO2 levels for this measurement? I know Hans has recommended this test, and I plan on getting it, but in the meantime, I was trying to see if I could figure these results out based on past testings.

Thank you, Pam,
Richard

Richard:
I don't think you need a separate test. Anion Gap in my opinion should be called Cation/Anion Gap as this is more descriptive of what the measurement actually reveals, as Na+ and K+ are cations and Cl and CO2 are Anions. Cations - Anions equals anion gap. Here's a better description than I can give. I'm sure more accurate as well.

The anion gap (AG) calculation is the sum of routinely measured cations minus routinely measured anions: (Na++K+) - (Cl-+HCO3-). However, because K+ is a small value numerically, it is usually omitted from the AG equation so that, as most commonly used,

AG = Na+ - (Cl- + HCO3-).

Although this is the equation most often published in articles and textbooks, for reasons discussed above the equation incorporates not the calculated arterial HCO3- but the measured venous CO2. To add to the confusion, some labs report the measured venous value as "HCO3-" and other labs as "CO2". Whatever the label for the reported venous value, that is the one you should use in calculating AG, since normal values are based on the venous electrolyte measurements. Throughout this book the anion gap will be calculated as

AG = Na+ - (Cl- + CO2).

OR - go to this link. It's very helpful also. Also talks about venous samples vs. arterial samples and arterial blood gas annalysis.

[www.mtsinai.org]

So, you see, you get the same gap without calculated HCO3.

Pam

Pam,

Thank you very much for the link and the explanation. Hope you're feeling better.

Richard