Anion Gap (Low)

Background

• < 7 meq/L

DDX

• Lab error
• Decreased "unmeasured" anions
  • hypoalbuminemia
• Increased "unmeasured" cations
  • hyperkalemia
  • hypercalcemia
  • hypermagnesemia
  • lithium intoxication
• 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)

• AG falls by 2.5 meq/L for every 1 g/dL reduction in albumin concentration

Source

Kaji Questions