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Nephrology

Serum Anion Gap (with albumin correction)

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Formula

AG = Na - (Cl + HCO3). Albumin-corrected AG = AG + 2.5 x (4.4 - albumin g/dL). Potassium is not included.

Limitations

  • The reference range is analyser- and laboratory-specific; 12 mmol/L is a conventional upper limit for Na - Cl - HCO3.
  • The albumin correction (0.25 mmol/L per g/L, that is 2.5 per g/dL, relative to a normal albumin of 44 g/L = 4.4 g/dL) follows Figge 1998; some sources use other factors or reference values.
  • Unmeasured paraproteins, severe hyperlipidaemia, and bromide or lithium interfere with the result.

References

  1. Clinical use of the anion gap. Emmett M, Narins RG. Medicine (Baltimore). 1977;56(1):38-54. PMID 401925
  2. Anion gap and hypoalbuminemia. Figge J, Jabor A, Kazda A, Fencl V. Crit Care Med. 1998;26(11):1807-1810. PMID 9824071