Anion Gap (Low)

Background

< 7 meq/L

DDX

1) Lab error

2) Decreased "unmeasured" anions

    a) hypoalbuminemia*

3) Increased "unmeasured" cations

    a) hyperkalemia

    b) hypercalcemia

    c) hypermagnesemia

    d) lithium intoxication

4) increased cationic paraprotein

    a) multiple myeloma (do a serum protein electrophoresis to w/o)

    b) polyclonal IgG gammopathy.

5) Pseudo

    a) severe hypernatremia (>170 meq/L)

         -true concentration of sodium is underestimated

    b) marked hyperlipidemia (marked overestimation of the plasma chloride concentration)

    c) bromide intoxication (e.g. for myasthenia gravis and some herbal medications)

• AG falls by about 2.5 meq/L for every 1 g/dL (10 g/L) reduction in the plasma albumin concentration

Source

Kaji Questions