Estimating unmeasured anions in critically ill patients: Anion-gap, base-deficit, and strong-ion-gap

D. A. Story, S. Poustie, R. Bellomo

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We used 100 routine blood samples from critically ill patients to establish whether correcting the anion-gap and base-deficit for decreased plasma albumin improves agreement with the strong-ion-gap for estimating unmeasured anions and whether the modifications increase the proportion of samples with levels of anion-gap or base-deficit above the reference ranges. We used Bland-Altman analyses to compare the methods of estimating unmeasured ions. Compared with the strong-ion-gap, modification reduced the limits of agreement for both the anion-gap and the base-deficit. The bias for the base-deficit was also reduced but the bias for the anion-gap was increased. The proportion of samples with an anion-gap > 22 meq.1-1 increased from 4 to 29% (p < 0.001), and the proportion with a base-deficit > 5 meq.1-1 increased from 8 to 42% (p < 0.001). Consequently, metabolic acidosis from unmeasured ions in critically ill patients maybe more frequent than often recognised.

Original languageEnglish
Pages (from-to)1109-1114
Number of pages6
Issue number11
Publication statusPublished - 1 Nov 2002
Externally publishedYes


  • Acid-base measurement

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