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Patients with sickle trait do not have sickle crises at all, except in very rare cases when they become seriously hypoxic. There are rare cases reported in military personnel and athletes. It's not clear whether they are sickle crises in some cases or just similar symptoms seen in non-sickle cell patients. These are truly rare cases, and usually at higher stress than an altitude of 8,000 feet, which really isn't terribly high. No personal experience. In extreme circumstances, patients heterozygous for S may be slightly more susceptible to symptoms like mountain sickness, just like everyone else. Don't know for sure. They have lower hematocrits and this may be one factor. Distinguishing between sickle cell symptoms and mountain sickness may be difficult for some clinicians. Lots of people get sick at altitude, especially if they exert themselves or make the ascent rapidly, or are dehydrated. I would guess that is what happened to this group. There is no need for hemoglobin S negative units for routine transfusions to non-sickle cell, hemoglobin homozygous patients.

The answer is a bit more complicated. If there is no target for %S, there is no need to test for hemoglobin S in donor blood. In other words, if the transfusion is purely for anemia, not treatment of acute chest syndrome or prevention of stroke, there is usually no target %S being used by the treating physician. The reason for testing for S in the donor is not the risk to the patient, but because transfusing S containing blood can confuse the calculation of % S overall. It's probably unnecessary because the %S contribution of a single unit of S heterozygous red cells in an exchange transfusion or red cell apheresis is very small. S hemoglobin in a red cell that is from a heterozygous donor does not contribute to sickling complications. This is well known because individuals who are heterozygous for S do not have complications of sickle cell disease. Thus while it is traditional to test for hemoglobin S in donor blood for sickle cell recipients, this is probably unnecessary unless the treating physician is trying to achieve a specific %S, as in stroke prevention.

People heterozygous for hemoglobin S have no clinical level problems with transporting oxygen, so there is no need (except for being overly cautious) to provide hemoglobin S tested blood for newborns, or, as I mentioned above, anyone who is not being monitored for % S. Another one of those "it seemed like a good idea at the time" but not evidence based approaches.