A patient of mine was told in the ED that she has sickle cell train and beta thalassemia, not sickle cell disease, and so can't be having a pain crisis. I have decided to turn my anger into something productive and make my first tweetorial: Types of Sickle Cell Disease

Sickle cell disease is a disease of hemoglobin. Hemoglobin is the thing in the red blood cell that carries oxygen. Everybody has two genes for hemoglobin, one from each parent. Each gene determines half of the hemoglobin that a person makes.

The "Normal" hemoglobin is called hemoglobin A. If a person has two genes that make hemoglobin A, than they are HbAA ,and 100% of their hemoglobin, and red blood cells, are normal.

Hemoglobin that can cause the red blood cells to take a sickled shape is called HbS. If a person has one gene for HbS and one for HbA, they are HbSA, 50% of their hemoglobin can sickle and 50% will not. This is sickle cell trait. The 50% HbA keeps them healthy most of the time

If a person has two genes for HbS, they are HbSS, and 100% of their hemoglobin can sickle. This is the most common type of sickle cell disease. We also call this sickle cell anemia.

There is another kind of abnormal hemoglobin called hemoglobin C. If a person gets one gene for HbS and one for HbC they have 50% S and 50% C hemoglobin, and are HbSC. The 50% C does not keep them healthy like HbA would, and so they also have sickle cell disease.

There is a disease called thalassemia where people make normal HbA, but less of it, we will call this HbB+. If someone has one gene for HbS and one for HbB+, they make 50% HbS, and very little HbA due to HbB+, so most of their blood is HbS and they have sickle cell disease.

There is a severe type of thalassemia where people make no HbA at all, we call this HbB0. If someone has one gene for HbS and one for Hb0, they are HbSB0. They make 50% HbS and no HbA, so all of their blood is HbS and they have sickle cell disease.

So, in summary. Sickle cell trait should not cause sickle cell disease, because the 50% HbA is protective. However, if someone has one gene for HbS and a second gene that is also abnormal like HbC or HbB+/HbB0, they will also develop sickle cell disease.

Finally, while the diseases classical hematologists care for are not benign, as people we tend to be. So if you have a question about a patient I am caring for, just ask me! But if you don't talk to me and accuse my patient of lying...