If the pH is abnormally low, this is acidosis. There is too much acid in the blood in relation to the amount of alkali. This could be caused by too much acid or not enough alkali; too much carbon dioxide, or not enough bicarbonate.

If the pH is abnormally high, this is alkalosis. There is too much alkali in the blood in relation to the amount of acid. This could be caused by too much alkali or not enough acid; too much bicarbonate, or not enough carbon dioxide.