This spring, I spent a month on the Hematology consult service. In theory this meant I ran around the hospital and tried to answer other people’s questions about the blood, but in practice it meant I came up with a number of questions of my own. All of them boiled down to something I’ve planned on addressing for some time: how can medicine use blood more wisely?
Not infrequently I wrote that patients’ caregivers should “transfuse as needed.” In some cases this was a passive-aggressive way of saying, “why did you call a hematology consult in the first place?” I wrote this in the charts of patients with myelodysplastic syndrome and anemia (where the bone marrow produces either too few blood cells or dysfunctional ones). I wrote it in the chart of patients with low platelets. Usually I didn’t clarify that statement – I left it up to the primary team to decide what would necessitate transfusion.
Transfuse as needed: part of the problem with the blood shortage is the liberal interpretation of that recommendation. What are the criteria for “as needed,” anyway, when it comes to transfusing blood?
There exist, of course, standards for transfusion of blood products. According to the Red Cross,
red blood cells are indicated for patients with a symptomatic deficiency of oxygen-carrying capacity or tissue hypoxia due to a decrease in circulating red cell mass. They are also indicated for exchange transfusion and red cell exchange.
If that sounds less than straightforward, the Red Cross thought so, too, and so they have attached a few numbers to help with the “decrease in red cell mass” part: a hemoglobin of greater than 10 grams per deciliter does not require transfusion, and a hemoglobin of less than 6 g/dL should be treated with transfusion (we'll say normal is 13 to 16 - a little higher than this for a man, a little lower for a woman). For platelets, the recommendations are similar: basically, use platelets if the person is bleeding and has either low numbers of platelets or adequate numbers of dysfunctional ones. The Red Cross also recommends prophylactic platelet transfusions: over 10,000 if the person is stable and not bleeding, for instance, and over 50,000 if the person is going to be undergoing an invasive procedure.
It’s the range from 6-10 where the Red Cross says to use your discretion, and it’s the range where I see transfusions whose benefit I sometimes doubt. “The lowest I’ve ever seen is a hemoglobin of one – and that person recovered,” said my attending one day as we discussed how to boost a patient’s hemoglobin before surgery. We gave her some intravenous iron, some folic acid (both required for blood-cell production) and finally a shot of erythropoietin, the hormone which stimulates the bone marrow to make more red cells. None of these things was going to have an effect before surgery, but still we wrote for them.
I got pretty used to seeing anemic patients over the course of a month, and I started to become desensitized to hemoglobins of 12, 11, 10. I wondered whether the body, too, became desensitized. Why not? We avoid dropping blood pressure too rapidly in people who routinely have higher pressures – not because it’s good to be hypertensive but because the body gets accustomed to the higher pressure. Does the body also get used to a lower hemoglobin level? An article in April’s issue of Transfusion starts to answer that question. The authors looked at both the absolute lowest concentration of hemoglobin during / after surgeries requiring cardiac bypass as well as the relative decrease in hemoglobin during or after surgery and related it to adverse outcomes. They found that the relative decrease in hemoglobin, not the absolute lowest value, was more important for outcome.
Later: how can we improve the system of blood donation?
