Definitions and abbreviationsa
| AG = ([Na+] + [K+]) − ([Cl−] + [HCO3−]) (normal range 14 to 16) or: |
| AG = [Na+] − ([Cl−] + [HCO3−]) (normal range 8 to 12) |
| AGc = observed AG + 2.5 × ([normal albumin] − [observed albumin]) = observed AG + 2.5 × (4.4 − [observed albumin]), where albumin concentration is in g/dl |
| A− = Primarily albumin and phosphate (in plasma) as well as hemoglobin (in whole blood) |
| ATOT = Total A− and its weak acid ([A−] + [HA]) |
| Buffer base = ([Na+] + [K+] + [Ca2+] + [Mg2+]) − ([Cl−]) = [HCO3−] + [A−] |
| BE or BD = Amount of acid or alkali that must be added to 1 L of whole blood to restore pH to 7.40 at Pco2 of 40 |
| SBE or SBD = BE or BD corrected for hemoglobin and size of interstitial fluid compartment; this can be calculated by dividing BE by 3 or calculating BE using hemoglobin of 5 g/dl |
| BEua = BE corrected for changes in free water, chloride, albumin, and Pco2 (used as a surrogate for SIG) |
| SID = ([Na+] + [K+] + [Ca2+] + [Mg2+]) − ([Cl−]) = [HCO3−] + [A−] |
| SIDa = ([Na+] + [K+] + [Ca2+] + [Mg2+]) − ([Cl−]) |
| SIDe = [HCO3−] + [A−] = 12.2 × Pco2/(10−pH) + [albumin in g/L] × (0.123 × pH − 0.631) + [PO4− in mmol/L] × (0.309 × pH − 0.469). |
| SIG = SIDa − SIDe |
↵a All units are in mEq/L, unless otherwise indicated. A−, nonbicarbonate buffers; AG, anion gap; AGc, AG corrected for albumin; ATOT, total weak acids; BD, base deficit; BE, base excess; BEua, BE contributed by unmeasured anions; SBD, standard base deficit; SBE, standard base excess; SID, strong ion difference; SIDa, apparent strong ion difference; SIDe, effective strong ion difference; SIG, strong ion gap.