Medical Laboratory Scientist (MLS) ASCP Practice Exam

What does low PCO2 indicate in terms of acid-base balance?

1. Represents acidosis

2. Represents alkalosis

3. Indicates respiratory failure

4. Indicates metabolic imbalance

The correct answer is: Represents alkalosis

Low PCO2 in the context of acid-base balance is indicative of alkalosis. This condition occurs when the concentration of carbon dioxide in the blood is reduced, leading to a higher pH level. PCO2 levels are closely linked to respiratory function; when a person hyperventilates, for example, they expel more CO2 than normal. This decrease in carbon dioxide leads to a decrease in carbonic acid, shifting the balance towards alkalinity. In clinical practice, hypoventilation can result in a rise of CO2 levels, subsequently causing acidosis, while conditions leading to hyperventilation drive CO2 levels down, contributing to respiratory alkalosis. Thus, the presence of low PCO2 is a critical indicator of respiratory alkalosis rather than being a sign of acidosis or other metabolic imbalances.