acid base...correcting Anion Gap for hypoalbumin

[bulldog]

I'm a little confused about correcting AG for hypoalbumin. In the blue book, it says take Na-HCO3-Cl = AG.

Corrected AG = calculated AG - (4-albumin)*2.5. So how do you interpret this?

Say Na 135, Cl 105, CO3 15. Albumin 2, pH 7.35
AG = 135-120 = 15.

Corrected AG = 15-(4-2)*2.5 = 10.

So this this mean this person doesn't have an AG adcidosis, as normal AG is 12?

When you calculated delta AG, is it based on corrected AG or serum AG?

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[BADMD]

I'm a little confused about correcting AG for hypoalbumin. In the blue book, it says take Na-HCO3-Cl = AG.

Corrected AG = calculated AG - (4-albumin)*2.5. So how do you interpret this?

Say Na 135, Cl 105, CO3 15. Albumin 2, pH 7.35
AG = 135-120 = 15.

Corrected AG = 15-(4-2)*2.5 = 10.

So this this mean this person doesn't have an AG adcidosis, as normal AG is 12?

When you calculated delta AG, is it based on corrected AG or serum AG?

I think you are backwards. The anion gap is approximately 3 times the albumin (although it is more complex than that and also includes the phosphorous). In this patient, you expect that anion gap to be around 6. To correct for the albumin difference, you want to add the correction factor to your calculated gap and not subtract. So, yes, this patient has an anion gap acidosis.

When you calculate the delta gap, you want to use the corrected (or expected AG). If I were doing this problem, I'd use an expected anion gap of 6 (although your assumptions may vary).

Delta AG is 15 - 6 or 9. CO2 is 15, so 9 + 15 is 24 and thus the delta gap is equal to 24 (assumed normal bicarb). Depending on what you take as your range (I'll assume no range), the patient has only an anion gap acidosis without a secondary acid base disorder.

You may have a different way of calculating delta gap, albeit a ratio or calculating a delta-delta gap.

 

[bulldog]

I think you are backwards. The anion gap is approximately 3 times the albumin (although it is more complex than that and also includes the phosphorous). In this patient, you expect that anion gap to be around 6. To correct for the albumin difference, you want to add the correction factor to your calculated gap and not subtract. So, yes, this patient has an anion gap acidosis.

When you calculate the delta gap, you want to use the corrected (or expected AG). If I were doing this problem, I'd use an expected anion gap of 6 (although your assumptions may vary).

Delta AG is 15 - 6 or 11. CO2 is 15, so 11 + 15 is 26 and thus the delta gap greater than 24 (assumed normal bicarb). Depending on what you take as your range (I'll assume no range), the patient has metabolic alkalosis on top of the anion gap acidosis.

You may have a different way of calculating delta gap, albeit a ratio or calculating a delta-delta gap.

check out this article: http://www.ncbi.nlm.nih.gov/sites/e...ez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSum

Seems like expected AG = AG + 2.5(4-albumin). In above example, it'd be 15+(4-2)*2.5 = 20. Giving you an anion gap (normal is up to 15 depending on institution).

To calculate the delta gap, if u're using the corrected value, it's:

dAG = 20-15 = 5. dHCO3 = 24-15 =9. Since dAG<dHCO3, giving u a non anion gap metabolic acidosis.

Edit: just corrected some math.

 

[BADMD]

Actually, I noticed I had a math error and th AG I calculated is 9, which yields no Delta gap.

You also have an error and should add 5 to your corrected AG and not 4.

Other than that, the differences in calculations are based on assumptions. You use a "normal" AG as being 15, I use 12 and I have difficuly applying an expanded range for a patient where I know the albumin, since normal includes hyperalbuminemic patients. Your correction factor corrects the patients normal AG to 7, whereas I'm using 6.

Of course there is far more than all that. AG is based mainly on albumin and phosphate. The valence of both change with the patient's pH. With the same concentrations, an alkylotic patient will have a wider AG than an acidotic patient. The delta gap calculation is very sensative to one's assumptions, thus you have to decide what is meaningful and what is not. I've seen some people say 6 is meaningful, but it is an ROC curve, so who knows.

I'm going to fix my math error above.

 

[bulldog]

Actually, I noticed I had a math error and th AG I calculated is 9, which yields no Delta gap.

You also have an error and should add 5 to your corrected AG and not 4.

Other than that, the differences in calculations are based on assumptions. You use a "normal" AG as being 15, I use 12 and I have difficuly applying an expanded range for a patient where I know the albumin, since normal includes hyperalbuminemic patients. Your correction factor corrects the patients normal AG to 7, whereas I'm using 6.

Of course there is far more than all that. AG is based mainly on albumin and phosphate. The valence of both change with the patient's pH. With the same concentrations, an alkylotic patient will have a wider AG than an acidotic patient. The delta gap calculation is very sensative to one's assumptions, thus you have to decide what is meaningful and what is not. I've seen some people say 6 is meaningful, but it is an ROC curve, so who knows.

I'm going to fix my math error above.

well, i think difference is i'm adding the corrected factor while u're subtracting the corrected factor. Say that the "normal" AG is 12...

dAG = 20-12 = 8. dHCO3 = 24-15 =9. Since dAG<dHCO3, giving u a non anion gap metabolic acidosis.

 

[BADMD]

well, i think difference is i'm adding the corrected factor while u're subtracting the corrected factor. Say that the "normal" AG is 12...

dAG = 20-12 = 8. dHCO3 = 24-15 =9. Since dAG<dHCO3, giving u a non anion gap metabolic acidosis.

If you look at what I'm doing, it is essentially the same. You are correcting your calculated anion gap to what you think it would be if the patient had a normal albumin, all other things being equal. I'm correcting what I think the patient's normal anion gap should be based on the albumin. The difference of 1 is what we assume the correction should be.