can anyone explain anion gap?

[coconut lime]

what exactly is anion gap? what does it represent clinically, like if it's high or low? how is it used in ddx? thanks!

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[eurotrash]

anion gap = (Na) - (HCO3 + CL)

represents unmeasured anions present in plasma

changes in anion gap represent acid base disturbances, the amount of the change represents the severity of the disturbance, if anion gap increases by the same amount that bicarb has decreased that means there is a single acid base disturbance (i.e. just metabolic acidosic), if change in anion gap not equal to change in bicarb you have a complex acid base disturbance where you may have a combination of acidosis and alkalosis. in such a case pH can remain in the normal range despite the presence of a serious problem.

actually i'm just messing with ya, i have no idea what an anion gap is

 

[omarsaleh66]

anion gap can be used to determine what type of acid/base disturbance u have; if there is one u can narrow down the choices to come up w a diagnosis. There are some acid/base problems that are nonanion gap. So i guess knowing the gap can help u narrow the diseases down and find the responsible acid base disturbance. and the above poster said most of it.


peace

Omar

 

[exmike]

Euro trash's equation was right.



You normally expect the Anion Gap to be about 10 mEq/L

You use the anion gap to determine if there is a base loss or acid load during acidosis.

Increased Anion Gap w/ Acidosis = acid load
This is because added acid will combine with HCO3-, eliminating the HCO3- and increasing the Gap

Normal Anion Gap w/ Acidosis = base loss (Na+ and HCO3- lost together as base loss, so gap remains the same)

 

[coconut lime]

thanks for the replies, they were very helpful.

 

[Kalel]

I agree with most of the previous posters. I just wanted to add that I find it helpful to remember that an anion gap is not a true "anion gap", it just means that there is some anion present in the blood that is not being measured (ie Cl, and bicarbonate). People are always isoelectric, that is total anions always equals total cations. There is always a "normal" anion gap because that "unmeasured" anion that is always present is albumin and other negatively charged proteins in our blood, and there is even a formula that some use to correct the anion gap for low albumin states. And finally, a neat mneumonic to help you remember the differential for an anion gap acidosis is MUD PILES.
M - Methanol
U - Uremia
D - Diabetic ketoacidosis
P - Paraldehyde (this drug is no longer used, but is known to keep the mneumonic going)
I - Iron, isoniazide
L - Lactic acidosis
E - Ethylene glycol intoxication
S - Salicylate intoxication

 

[Harrie]

Small or negative anion gap, think multiple myeloma, Waldenstrom's macroglobulinemia, etc.

 

[Fermi]

MUD PILES.
M - Methanol
U - Uremia
D - Diabetic ketoacidosis
P - Paraldehyde (this drug is no longer used, but is known to keep the mneumonic going)
I - Iron, isoniazide
L - Lactic acidosis
E - Ethylene glycol intoxication
S - Salicylate intoxication

I love MUDPILES. I believe you can also use Starvation Ketoacidosis for the "S."