Increased anion gap in metabolic acidosis

[Hemichordate]

Is the increased anion gap in metabolic acidosis solely due to the decreased bicarbonate, or can it be due to decreased chloride as well?

Likewise, in normal anion gap metabolic acidosis, is the bicarbonate still decreased?

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[Astarael]

The gap is due to an increased amount of some other anion; specifically, one that isn't measured. Since you always have to maintain eloctroneutrality, when bicarbonate goes down (the primary disturbance in metabolic acidosis), it has to be replaced by either chloride or another anion. If it's replaced by chloride, you won't see a gap, and if it's replaced by an unmeasured anion, you will.

In normal anion gap acidosis, bicarbonate is decreased. That is the definition of the "metabolic" part of acidosis.