Anion gap
Background
AG = Na - (Cl + HCO3)
Normal Anion Gap = 12+/-4 (8-16)
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
DDx
MUDPILES
- M - Methanol
- U - Uremia
- D - DKA
- P - Paraldehyde
- I - Iron, INH
- L - Lactic acidosis
- E - Ethylene glycol
- S - Salicylates
Also:
- Starvation/ETOH ketoacidosis
- CO, CN poisoning (incr. lactate)
- toluene
Low Anion Gap
DDX
- 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 intoxication (e.g. for myasthenia gravis and some herbal medications)
- Machine mistakenly reads Br as Cl
- 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)