A primary acid-base imbalance occurs when an overwhelming amount of acid or base causes an imbalance with homeostasis. A metabolic acidosis occurs when the kidneys are not able to excrete enough metabolic acid or produce enough bicarbonate to equal the amount of acid. Metabolic alkalosis occurs when the kidneys produce too much bicarbonate and not enough acid is reabsorbed to counter the increased bicarbonate.

In respiratory acidosis too much carbonic acid is retained, causing a buildup of CO₂, and not enough bicarbonate exists to compensate the increased carbonic acid. Respiratory alkalosis occurs when too much carbonic acid is expelled as CO₂ and not enough metabolic acid is available to counteract for the lack of CO₂.