Ask the Doctors

What can cause high carbon dioxide levels in the blood?

Howard LeWine, M.D., is chief editor of Internet Publishing at Harvard Health Publications. He is recognized as an outstanding clinician and teacher and is a recipient of the Internal Medicine Teacher of the Year award at Brigham and Women's Hospital. Dr. LeWine continues to practice Internal Medicine; most recently he became a hospitalist after practicing primary care for over 20 years.

Question:

My most recent blood test showed a high carbon dioxide level. What can cause this?

Answer:

Similar to any lab test, a high carbon dioxide level must be interpreted based on the person's situation.

This includes:

  • Why the test was done
  • What were the symptoms, if any
  • What medical problems or conditions does the person have

The normal range for almost all blood tests is determined by looking at average levels in a large group of otherwise healthy people. This is certainly true for blood CO2 levels.

An "abnormal" number means you are not in the average range. But it doesn't always mean there is a problem. Some healthy people will simply have carbon dioxide levels that are slightly higher (or lower) than average.

There's probably nothing wrong when the carbon dioxide level is just a point or two above the normal range. That's particularly true if you felt fine and your test turned up abnormal on otherwise routine blood work.

On the other hand, there should be an explanation for a blood carbon dioxide level that's much higher than normal.

Some reasons for a high carbon dioxide level include:

  • Severe breathing problems, such as emphysema
  • Vomiting for a long period of time
  • Taking high doses of diuretics or antacids
  • Certain hormone conditions that cause acids to leak into the urine
  • Low blood levels of potassium