An Update on the Clinical Usefulness of Anion Gap in a Selected Category of Patients

Abstract

Anion gap is an important parameter used in the interpretation of acid base disorders. This study is undertaken to update the recent understanding of the clinical usefulness of Anion gap in a selected category of patients in our Hospital. Anion Gap and 95 % confidence limits were calculated using the results for Na, Cl and HCO3 of 200 non hospitalized out patients, 300 MICU hospitalized patients, 110 neonatal hospitalized patients and 51 normal male blood donors. Standard procedure was used to collect random blood samples. Beckman coulter AU400 analyzer which employs ISE direct principle was used to measure Na / K / Cl and enzymatic method for HCO3. Appropriate assayed accuracy controls from Bio-Rad were used to validate the accuracy of the results obtained. As this study was to update the usefulness of anion gap, selection of patients with respect to inclusion or exclusion criteria were not followed. The mean + 2 SD limits obtained for blood donors were Na: 131-143, K: 3.4-4.6 Cl: 97-107, HCO3: 21-29 and AG 6-14, (all in mmol / L) all of which agree well with the normal values used in this laboratory. While AG range for blood donors was 6 to 14, for out patients it was 4 to 16, for MICU group it was 3 to 19 and for neonates 1-23 suggesting that MICU and Neonates group patients may have different types of Acid base disorders. MICU patients AG were more or less close to normal blood donors. The AG range for neonates was the widest ranging from 1 to 23. This study gives some awareness on the usefulness of AG in interpreting acid base disorders.