Compensation refers to the degree of PCO2 change when there is, or has been, an abnormality in pH.

An uncompensated disorder is a primary metabolic or respiratory condition that has not been altered by any significant degree of correction. In the case of a primary metabolic condition the respiratory counterbalance (change in ventilation which is reflected by a change in arterial PCO2) is not evident; pH is abnormal but PCO2 remains normal. In the case of a primary respiratory condition, both PCO2 and pH are abnormal, and the degree of abnormality on both tests is relatively severe. In that case the renal counterbalance (increased bicarbonate formation to bring pH back toward normal) is not evident.

A partially compensated disorder is present when both pH and PCO2 are outside their reference ranges. In primary respiratory disorders, the degree of pH abnormality is not as severe as in uncompensated cases.

A fully compensated (sometimes referred to only as compensated) condition is a primary metabolic or respiratory disorder in which PCO2 is outside its reference range but pH has returned to its reference range.