Whenever I order arterial blood gases (ABGs), the report includes hemoglobin levels. How do these levels correlate with the hemoglobin levels on a complete blood count (CBC)? Can management decisions be made using these data?
—J.C. Fuentes, MD, Houston
These are excellent questions, as the ABG results are usually available much more quickly than a traditional CBC. A recent article addressed these very questions in the critically ill (Crit Care. 2002;6:72-75). Comparison of hemoglobin concentrations in each blood sample using a blood gas analyzer and a conventional laboratory Coulter counter found that the values correlated very closely. The ABG analyzer overestimated the hemoglobin minimally (approximately 4%), which would not be clinically significant. The authors concluded that hemoglobin measurements from an ABG provide a valid alternative method to a traditional CBC but qualified these findings with the statement that “since issues related to its safety, quality control, data entry, and cost savings have yet to be addressed…such point-of-care testing should be [used only as a supplement] to conventional laboratory testing.”
—Susan Kashaf, MD, MPH (112-10)