A: I think that the most important thing I can tell you about this question is that is based on a misconception (a popular misconception, by the way, but still a misconception!).
In my opinion, and in that of a growing number of physicians, there really is not a particular threshold hemoglobin or hematocrit at which you can say "OK, that's it. This patient definitely needs a transfusion."
If you have been around Blood Banks or operating rooms for very long, you know that in the eyes of many clinicians, a hematocrit level of 30% (corresponding to a hemoglobin level of 10 g/dL) has traditionally served as the "threshold" for transfusion of red cells. In other words, if the patient's hematocrit is below 30%, doggone it, get it above 30%! What many of us don't know is that this value came from some papers published by Mayo Clinic physicians just after World War II (yep, over 50 years ago!) that suggested that people in that era with hemoglobin levels between 8 and 10 g/dL did better after surgery. From that, we ended up with the general, widely held feeling that 10 was the threshold hemoglobin!
Remember, many clinicians initially learned their transfusion medicine in exactly the wrong way: From a tired resident, fellow student or intern, or even worse, from an attending who was taught the wrong way himself! It's really not too hard to understand how the 30% "trigger" came into common usage and acceptance.
Currently, though, consensus and practice parameter papers have come from all specialties containing variations on the same theme: The 30% "trigger" is obsolete! Rather, the preferred method of deciding whether or not to transfuse is to evaluate each patient on a case-by-case basis, taking into account the medical (especially cardiac and pulmonary) history, ability to compensate for a lower hemoglobin, medication history (beta blockers limit compensatory tachycardia in anemia, for example), and rate of hemoglobin decline to decide on the utility of a transfusion. Studies have clearly shown that many people can tolerate lower hemoglobin levels than we used to think they could, especially if they have proper compensatory mechanisms (ability to increase cardiac output, etc.).
Let's not be ridiculous here, OK? Obviously, if someone had a hemoglobin of 2 g/dL, everyone on the planet would argue that red cell transfusion was indicated! I'm referring primarily to patients with hemoglobin somewhere in the 7-10 range, where there is still somewhat of a choice.
— Blood Bank Guy
So, the bottom line is simply this: automatic thresholds are simply inappropriate when applied "across the board". A better strategy is to assess each patient and decide what this patient's threshold is, based on clinical and laboratory findings, as well as patient history.
A final word of caution to laboratorians: It is easy for those of us who are sitting in the Blood Bank to go overboard in criticizing our clinician friends. While clinicians sometimes tend to rely too much on arbitrary thresholds like the 30 percent rule, we tend to go overboard the other way. In other words, we want clinicians to rely too much on clinical data. If we suggest to our docs that they should wait until their patient is having chest pains or EKG changes before they transfuse (while we are guarding the door to our Blood Bank with a fiery sword), we look like idiots, quite honestly! Can't we all just get along?
— Blood Bank Guy
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