Anion gap (with albumin correction)

Base anion gap = sodium − (chloride + bicarbonate). The potassium-inclusive anion gap = (sodium + potassium) − (chloride + bicarbonate), which runs about 3.5 to 5 units higher and uses a higher reference interval, so the two forms are shown separately. The albumin-corrected anion gap = anion gap + 2.5 × (4.0 − albumin in g/dL) (Figge 1998), so each 1 g/dL below 4.0 adds 2.5 mEq/L, unmasking a high-anion-gap acidosis that hypoalbuminemia would hide. mEq/L and mmol/L are numerically equal for these ions, and total CO₂ is used interchangeably with HCO₃.

No interpretation bands are emitted. Reference intervals are strongly method-dependent: flame photometry gave about 12 ± 4 mEq/L, ion-selective electrodes shifted it to about 6 ± 3, and verified intervals span, for example, 10 to 18. Classify against the reporting lab’s own interval, never a fixed cutoff, and never compare a potassium-inclusive value with a potassium-exclusive range. The anion gap is a diagnostic index, not a severity score. The albumin correction increases sensitivity, not specificity, and is an adjunct to direct measurement of lactate and ketones. The 2.5 coefficient and the reference intervals are adult-derived, applied to children by convention. Spurious electrolytes (pseudohyponatremia, bromide interference) distort the gap directly.