Anion gap: Difference between revisions
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==Background== | ==Background== | ||
AG = Na - (Cl + HCO3) | A normal gap is 12 +/- 4 (i.e. 8 to 16). The anion gap is the difference between measured cations and measured anions in serum. This difference does not reflect a true disparity between positive and negative charges, given that serum actually | ||
is electrically neutral when all serum cations and anions are measured. Rather, the anion gap is a measurement artifact resulting | |||
Normal Anion Gap = 12+/-4 (8-16) | from the fact that only certain cations and anions are routinely measured. Anion gap metabolic acidosis is secondary to the addition of endogenous or exogenous acid | ||
*AG = Na - (Cl + HCO3) | |||
*Normal Anion Gap = 12+/-4 (8-16) | |||
*12-20 mEq/L when including K+ | |||
Cutoffs for "normal" Anion Gap are laboratory and equipment specific. Newer technology and equipment have been shown to measure "low" AG in otherwise normal, healthy people.<ref>Jurado RL, del Rio C, Nassar G, Navarette J, Pimentel JL Jr. "Low anion gap." South Med J. 1998;91(7):624</ref><ref>Winter SD, Pearson JR, Gabow PA, Schultz AL, Lepoff RB. "The fall of the serum anion gap." Arch Intern Med. 1990;150(2):311</ref> | Cutoffs for "normal" Anion Gap are laboratory and equipment specific. Newer technology and equipment have been shown to measure "low" AG in otherwise normal, healthy people.<ref>Jurado RL, del Rio C, Nassar G, Navarette J, Pimentel JL Jr. "Low anion gap." South Med J. 1998;91(7):624</ref><ref>Winter SD, Pearson JR, Gabow PA, Schultz AL, Lepoff RB. "The fall of the serum anion gap." Arch Intern Med. 1990;150(2):311</ref> | ||
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===Differential Diagnosis=== | ===Differential Diagnosis=== | ||
MUDPILES | MUDPILES | ||
*M - [[Methanol]] | *M - [[Methanol]], [[metformin]] | ||
*U - [[Uremia]] | *U - [[Uremia]] | ||
*D - [[Diabetic Ketoacidosis (DKA)|DKA]] | *D - [[Diabetic Ketoacidosis (DKA)|DKA]] | ||
*P - Paraldehyde | *P - Paraldehyde, phenformin | ||
*I - [[Iron Toxicity|Iron]], INH | *I - [[Iron Toxicity|Iron]], INH, [[ibuprofen]] (large ingestions) | ||
*L - [[Lactic acidosis]] | *L - [[Lactic acidosis]] | ||
*E - [[Ethylene glycol]] | *E - [[Ethylene glycol]] | ||
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Also: | Also: | ||
*Starvation/[[Alcoholic ketoacidosis|ETOH ketoacidosis]] | *Starvation/[[Alcoholic ketoacidosis|ETOH ketoacidosis]] | ||
*[[Carbon monoxide toxicity| Carbon Monoxide (CO)]], [[Cyanide|CN poisoning]] (increased [[lactate]]) | *[[Carbon monoxide toxicity| Carbon Monoxide (CO)]], [[Cyanide|CN poisoning]] (increased [[lactate]]), [[colchicine]] | ||
*Toluene | *Toluene | ||
*Chronic [[acetaminophen]] use | *Chronic [[acetaminophen]] use | ||
KILR | |||
*K – [[Ketoacidosis]] - ([[Diabetic ketoacidosis (DKA)|diabetic]], [[Alcoholic ketoacidosis|Alcohol]], Starvation) | |||
*I – [[Toxicology (Main)|Ingestion]] - ([[Aspirin (Salicylate) Toxicity|Salicylates]], [[Acetaminophen]], [[Methanol]], [[Ethylene glycol]], [[Carbon monoxide toxicity|CO]], [[Cyanide|CN]], [[Iron toxicity|Iron]], [[INH toxicity|INH]]) | |||
*L – [[Lactic acidosis]] - (infection, hemorrhage, hypoperfusion, [[Alcohol]], [[Metformin]]) | |||
*R – Renal - ([[Uremia]]) | |||
==Low Anion Gap== | ==Low Anion Gap== | ||
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*Lab error | *Lab error | ||
*Decreased "unmeasured" anions | *Decreased "unmeasured" anions | ||
**Hypoalbuminemia | **[[Hypoalbuminemia]] | ||
*Increased "unmeasured" cations | *Increased "unmeasured" cations | ||
**[[Hyperkalemia]] | **[[Hyperkalemia]] | ||
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**[[Lithium Toxicity]] | **[[Lithium Toxicity]] | ||
*Increased cationic paraprotein | *Increased cationic paraprotein | ||
*Multiple myeloma | *[[Multiple myeloma]] | ||
**Polyclonal IgG gammopathy | **Polyclonal IgG gammopathy | ||
*Pseudo | *Pseudo | ||
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**Marked hyperlipidemia | **Marked hyperlipidemia | ||
***Leads to overestimation of plasma Cl conc) | ***Leads to overestimation of plasma Cl conc) | ||
**Bromide | **[[Bromide toxicity]] (e.g. for [[myasthenia gravis]] and some herbal medications) | ||
*** | ***Assay mistakenly reads Br as Cl | ||
***May have negative anion gap | |||
**Elevated serum iodide | |||
*AG falls by 2.5 meq/L for every 1 g/dL reduction in albumin concentration | *AG falls by 2.5 meq/L for every 1 g/dL reduction in albumin concentration | ||
==See Also== | ==See Also== | ||
[[Anion Gap and Osmolar Gap (High)]] | *[[Anion Gap and Osmolar Gap (High)]] | ||
*[[Anion Gap (High)]] | |||
*[[Osmolal or Osmolar Gap]] | |||
*[[Toxidromes]] | |||
*[[Acidosis]] | |||
==External Links== | |||
*[http://www.mdcalc.com/serum-osmolality-osmolarity/ MDCalc - Serum Osmolality/Osmolarity] | |||
*[http://www.mdcalc.com/anion-gap/ MDCalc - Anion Gap] | |||
== | ==References== | ||
<references/> | <references/> | ||
[[Category:FEN]] | [[Category:FEN]] | ||
[[Category: | [[Category:Toxicology]] | ||
[[Category:Critical Care]] | |||
Latest revision as of 03:02, 21 February 2021
Background
A normal gap is 12 +/- 4 (i.e. 8 to 16). The anion gap is the difference between measured cations and measured anions in serum. This difference does not reflect a true disparity between positive and negative charges, given that serum actually is electrically neutral when all serum cations and anions are measured. Rather, the anion gap is a measurement artifact resulting from the fact that only certain cations and anions are routinely measured. Anion gap metabolic acidosis is secondary to the addition of endogenous or exogenous acid
- AG = Na - (Cl + HCO3)
- Normal Anion Gap = 12+/-4 (8-16)
- 12-20 mEq/L when including K+
Cutoffs for "normal" Anion Gap are laboratory and equipment specific. Newer technology and equipment have been shown to measure "low" AG in otherwise normal, healthy people.[1][2]
Elevated Anion Gap
Differential Diagnosis
MUDPILES
- M - Methanol, metformin
- U - Uremia
- D - DKA
- P - Paraldehyde, phenformin
- I - Iron, INH, ibuprofen (large ingestions)
- L - Lactic acidosis
- E - Ethylene glycol
- S - Salicylates
Also:
- Starvation/ETOH ketoacidosis
- Carbon Monoxide (CO), CN poisoning (increased lactate), colchicine
- Toluene
- Chronic acetaminophen use
KILR
- K – Ketoacidosis - (diabetic, Alcohol, Starvation)
- I – Ingestion - (Salicylates, Acetaminophen, Methanol, Ethylene glycol, CO, CN, Iron, INH)
- L – Lactic acidosis - (infection, hemorrhage, hypoperfusion, Alcohol, Metformin)
- R – Renal - (Uremia)
Low Anion Gap
Differential Diagnosis
- Lab error
- Decreased "unmeasured" anions
- Increased "unmeasured" cations
- Increased cationic paraprotein
- Multiple myeloma
- Polyclonal IgG gammopathy
- Pseudo
- Severe Hypernatremia (>170 meq/L)
- True conc of Na is underestimated
- Marked hyperlipidemia
- Leads to overestimation of plasma Cl conc)
- Bromide toxicity (e.g. for myasthenia gravis and some herbal medications)
- Assay mistakenly reads Br as Cl
- May have negative anion gap
- Elevated serum iodide
- Severe Hypernatremia (>170 meq/L)
- AG falls by 2.5 meq/L for every 1 g/dL reduction in albumin concentration