An arterial blood gas or ABG is a blood test used to evaluate certain gases and chemicals in your blood. Most blood tests require blood from your vein. ABGs require blood from your artery. The ABG test results show your blood levels of pH, carbon dioxide, bicarbonate and oxygen. The ABG is an important tool in evaluating how your lungs are functioning. Even though it's never the only test used to diagnose an illness, it's important to understand the results. Once you learn the three key components of an ABG, it's easy to interpret the results.
Hydrogen ions in your blood are measured by pH. The hydrogen ions regulate the acid and alkaline in your blood. If your pH is high, it's called alkalosis. If your pH is low, it's called acidosis. A range of 7.35 to 7.45 is normal; below 7.35 shows acidosis; and above 7.45 shows alkalosis.
PaCO2 is the partial pressure of carbon dioxide. This is a measure of how much carbon dioxide is in your blood. An abnormal PaCO2 level tells you there is a respiratory problem. A range of 35 to 45 is normal; below 35 shows alkalosis; and above 45 shows acidosis.
HCO3 is the bicarbonate level in your blood. The bicarbonate keeps your pH balanced so there isn't too much acid or alkaline. An abnormal level of bicarbonate tells you there is a metabolic problem. A range of 22 to 26 is normal; below 22 shows acidosis; and above 26 shows alkalosis.
A respiratory acidosis happens when you have an acidic pH and too much carbon dioxide. Your bicarbonate will be normal. Any abnormal CO2 level is a sign of a respiratory problem.
A respiratory alkalosis happens when you have too much alkaline and too little CO2. Your bicarbonate will be normal. Any abnormal CO2 level is a sign of a respiratory problem.
A metabolic acidosis happens when you have an acidic pH and a low bicarbonate level. Your PaCO2 will be normal. Any abnormal bicarbonate level is a sign of a metabolic problem.
A metabolic acidosis happens when you have an alkaline pH and a high bicarbonate level. Your CO2 level will be normal. Any abnormal bicarbonate level is a sign of a metabolic problem.