Anion gap: Difference between revisions
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*Decreased "unmeasured" anions | *Decreased "unmeasured" anions | ||
**Hypoalbuminemia | **Hypoalbuminemia | ||
*Increased "unmeasured" cations | *Increased "unmeasured" cations | ||
**[[Hyperkalemia]] | **[[Hyperkalemia]] | ||
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**Marked hyperlipidemia | **Marked hyperlipidemia | ||
***Leads to overestimation of plasma Cl conc) | ***Leads to overestimation of plasma Cl conc) | ||
** | **[[Bromide toxicity]] (e.g. for [[myasthenia gravis]] and some herbal medications) | ||
***Assay mistakenly reads Br as Cl | ***Assay mistakenly reads Br as Cl | ||
***May have negative anion gap | |||
**Elevated serum iodide | **Elevated serum iodide | ||
Revision as of 22:37, 18 February 2016
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
- U - Uremia
- D - DKA
- P - Paraldehyde
- I - Iron, INH
- L - Lactic acidosis
- E - Ethylene glycol
- S - Salicylates
Also:
- Starvation/ETOH ketoacidosis
- Carbon Monoxide (CO), CN poisoning (increased lactate)
- 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
- Hypoalbuminemia
- 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
See Also
Anion Gap and Osmolar Gap (High)