- What is Anemia
- Sickle Cell Disease
- Alpha Thalassemia
- Beta Thalassemia
- Autoimmune Hemolytic Anemia
- Warm vs Cold AIHA
- Paroxysmal Nocturnal Hemoglobinuria
On the blood test, Anemia will show low Hematocrit, low Hemoglobin and low Red Blood cell counts. There is one anemia in Beta Thalassemia where you can have higher levels of RBCs in the 6 million range, but all others will show low levels of RBCs. The types of anemia are broken down into 3 categories with microcytic, normocytic and macrocytic based on the MCV levels.
The Microcytic anemias consist of the type of anemia where the red blood cells can't form enough healthy cells. We know as the Red Blood Cell matures, it gets smaller and smaller. The microcytic anemias have small red cells with a MCV below 80 fl. This is because they wait and wait for all the proper materials like Iron, protoporphyrin or globin proteins. When they can't get enough, they end up just making smaller Red Blood Cells. This includes Iron Deficiency Anemia, Thalassemia and Sideroblastic Anemia. I have talked about Iron deficiency and Thalassemia before as they are the most common forms of microcytic anemias. Sideroblastic anemia has a genetic form, but most of the cases are acquired sideroblastic anemia which comes from toxins like Lead poisoning. In Sideroblastic anemia, the iron clumps up to make small visible clumps which makes them look like basophils. These can often be seen in the bone marrow or a blood smear. We call this Basophilic Stippling.
Thalassemia comes in 2 forms with Alpha and Beta Thalassemia. This is a genetic disease where there is a loss of one or more of the genes that makes the globin proteins for the hemoglobin. In Alpha Thalassemia, the red blood cells make little or no Alpha globin proteins. In Beta Thalassemia, the red blood cells will make little to no beta globin proteins. Depending on how severe the Thalassemia is, they will make very little to no globins which are necessary for the 2 alpha globin and 2 beta globin structure of the Hemoglobin. What ends up happening is you get hemoglobin made with 4 alpha proteins or 4 beta proteins. They work, but those RBCs tend to die very quickly when they reach circulation. Then you have hemolysis.
The last microcytic anemia is Iron Deficiency. This is the most common form of anemia worldwide due to malnutrition. In the developed world, there are genetic disorders that can lead to iron deficiency. These tend to be absorption disorders like Celiacs Disease. The most common are related to high cell growth like child development or pregnancy.
Next up is the Macrocytic anemias. These have very large cells as they tend to release very large and immature Red Blood cells. They tend to have a MCV over 100 fl. The Macrocytic anemias get divided into Megaloblastic and Non megaloblastic. The Megaloblastic will be accompanied with hypersegmented neutrophils. The typical neutrophil will have 3 to 5 lobes in its nucleus. These hypersegmented neutrophils will have 7 or more lobes. The 2 major Megaloblastic Anemias are B12 deficiency and Folate deficiency. These are nutritional anemias. These are easily corrected with a high dose of intramuscular B12 or Folate. They are often nutritional and can be related to GI diseases. The one thing that stands out about B12 deficiency is it can come with some neurocognitive symptoms. These can be in the form of mood changes to memory loss. This is the one key factor that separates B12 from Folate deficiency.
The top 3 causes of Non Megaloblastic anemia is Liver Disease. Alcoholism and Medications. All of these we will not dive into. This brings us back to the normocytic anemias. These get subdivided into the intrinsic defects and extrinsic defects of the RBC. Intrinsic are those anemias that stem from a genetic defect of the RBC like the spherocytosis and elliptocytosis from the structure protein defects. Then there is Sickle Cell anemia which comes from a mutation in the Beta Globin. Sickle Cell anemia will cause the hemoglobin to polymerize when in a low Oxygen environment leading to the sickling of the RBC.
Next would be a G6PD which comes from a missing enzyme which helps convert Oxygen radicals back into water to clear them. This leads to the build up of O2 radicals. This is important with beans like Fava Beans. They can lead to G6PD attacks. The next will be Paroxysmal Nocturnal Hemoglobinuria (PNH). This is a defect in the proteins that get made on the cell surface to defend cells from being attacked by the complement system. Most of these normocytic anemias are the destruction anemias where the Red Blood Cells get destroyed.
Sickle Cell Disease
The actual disease of SCD is caused by a single base mutation in the Hemoglobin Beta (HbB) gene that makes the HbB protein as part of the Hemoglobin. This single change encodes a different amino acid. The properties of this different amino acid causes the HbB to bind together into long strands under low oxygen conditions. This in turn causes the Red Blood cell to take on a Sickle like shape. We call this form of Hemoglobin Beta HbS for Sickling.
The HbS gene is prominent in Africa with 1 in 365 Africans having the HbS gene. It has a lower occurrence in Asians and some South Americans. This gene is very prominent in areas of the world where Malaria is endemic. Malaria is an infectious disease carried by mosquitoes. This disease infects red blood cells. The HbS makes these cells resistant to infection by Malaria. This is why this allele of the HbB gene has evolved. A single copy of the HbS gene will offer protection from a horrible infectious disease, but getting 2 copies of this gene leads to Sickle Cell Disease. This disease works in an Autosomal Recessive capacity. That means each person gets 2 copies of the HbB gene (1 from mom and 1 from dad). To get SCD, the patient has to inherit one copy of the HbS gene from both mom and dad. That means mom and dad both must be at least carriers of that trait. The world has about 300,000 cases of SCD each year with the vast majority coming from Africa. Many of these cases are in countries where healthcare is not available. The US cases of SCD is 90,000 with about 2,000 births per year.
When a baby is first born, they will still be producing Fetal Hemoglobin (HbF). This is made up of alpha and gamma proteins. By 6 months of age, they will be developing Red Blood cells with Adult Hemoglobin. The Adult Hemoglobin (HbA) will be made up of 2 alpha and 2 beta chains. This is when the HbS will show up as the infant begins to make adult hemoglobin with the mutated HbS gene. The symptoms of SCD are Anemia. The blood counts will show anemia with Low Hematocrit and Low Hemoglobin levels. You would see Hematocrit around 25% and Hb around 9 or less. This is the first sign of Sickle Cell. The iron studies will typically be normal which rules out iron deficiency. You will have signs of Hemolysis with elevated LDH, Unconjugated Bilirubin, and low Haptoglobin. This is because these Red Blood cells with the HbS will not live as long as healthy RBCs. The typical RBC lives about 120 days. The SCD red blood cell will live about 20 days.
This means a lot of cells are being destroyed in the vessels (intravascular) and the spleen (extravascular). Due to the Sickling shape of these Red blood cells, you can get what are called Sickle cell crisis and Vaso Occlusive Crisis. This comes from the sickled cells blocking veins. When they block up the smaller veins in the tissue or bone marrow, it can cause a very painful crisis. Many of these patients end up hospitalized with opioid use. These sickled cells can also restrict blood flow causing potentially life threatening Vaso Occlusive Crisis. This can lead to stroke or heart attacks. The last major symptom is Splenomegaly. This is an enlargement of the spleen. This is also caused by the trapping of sickle cells in the spleen. Most SCD patients will end up with getting their spleen removed. The treatment for SCD is Hydroxyurea which helps boost the production of Fetal hemoglobin. It offers modest benefits to boost Hematocrit and Hb.
There are gene editing programs in development that extract the stem cells from the bone marrow of the patient. They edit these cells to switch them back to making healthy fetal Hemoglobin. They will deplete the remaining stem cells from the bone marrow and replace them. They put the corrected stem cells back into the patient. This is a long and complex process of extraction of stem cells, manufacturing and administration of the new cells after a very toxic Busulfan Myeloablation. This does offer possible functional cures to patients based on the data.
The incidence rate of Alpha Thalassemia is about 1 in 100,000 people in North America. There is estimated to be around 1,200 transfusion dependent patients in the US. The occurrence of Alpha Thalassemia is in Mediterranean regions of Southern Europe, Middle East and Northern Africa. It is also seen in people from India and Asia.
Hemoglobin in Red Blood cells is made up of 2 alpha proteins and 2 beta proteins. The alpha Thalassemia stems from mutations in the genes that make up the alpha proteins. You get 2 copies of the Alpha gene from Mom and 2 from Dad for a total of 4. The mutations that occur in the alpha gene locus are deletion mutations. This results in the complete loss of 1 to all 4 of the genes for the alpha proteins. The loss of 1 gene is represented like (aa/a-). This leads to the Alpha Thalassemia trait. These patients will be otherwise completely normal. They have the ability to pass that trait to their children in an autosomal recessive fashion. Alpha Thalassemia Minor comes from the loss of 2 of the 4 genes. This can be both from the same parent or one from each parent. This is represented by (a-/a-) or (aa/--). This leads to a mild microcytic anemia, but these patients are otherwise very healthy. The loss of 3 of the 4 genes leads to Alpha Thalassemia Major or Hemoglobin H (HbH) disease. This is named such because the alpha protein levels will be so low the Hemoglobin will start forming with 4 beta proteins. This is represented as (a-/--).
These patients will have severe anemia with other symptoms. They will have a low Hematocrit and Hemoglobin showing Anemia. They will have a low MCV showing microcytic. They will have an enlarged spleen due to extravascular hemolysis. They will have signs of hemolysis with elevated Bilirubin and LDH levels. The Red Blood cells they make will be misshaped. They will be destroyed in the Spleen nearly as fast as they are made.
The treatment for Alpha Thalassemia Major is frequent blood transfusions. Each time blood is given, all those red blood cells bring with them more iron. This leads to iron overload. Then they need chelation therapy to remove the iron.
The last form of Alpha Thalassemia is the loss of all 4 alpha genes. This is referred to as Bart's Disease. This leads to spontaneous loss of the fetus. If you recall back to our previous sections, we said that an embryo made HbE until it became a fetus which started producing Fetal Hb (HbF). Fetal Hemoglobin requires alpha chains of which there will be none with the loss of all 4 genes. This results in Hydrops Fetalis which is the loss of the fetus.
Like Alpha Thalassemia, Beta Thalassemia is very prominent in the Mediterranean area with Southern Europe, Middle East and Northern Africa. It is also in Asia at a lower rate. It has the same rate of incidence as Alpha Thalassemia at 1 per 100,000 people in the population. It is estimated that about 1,300 people in the US have Beta Thalassemia. This form of Thalassemia will present around 6 months of age as the baby goes from making Fetal Hb which has Gamma globins to making Adult Hb which uses the Beta Globins.
Hemoglobin in Red Blood cells is made up of 2 alpha proteins and 2 beta proteins. The Beta Thalassemia disease stems from mutations in the genes that make up beta proteins. You get just 1 copy of the Beta Globin gene from each parent. The defects in this gene are single point mutations. This means just a single base has been changed. There are many different mutations, but they are usually in the promoter region or the splicing regions. This results in one of two possible outcomes for the Beta Protein. You can either end up with a protein that is partially functional or one that is completely non functional. That leaves the Beta gene with 3 possible states. The first is the fully functional normal gene represented at Beta (B). The second is the partially functional gene which is represented Beta Plus (B+). The third is the non functional gene which is represented as Beta Zero (B0).
This leaves us with 3 forms of Beta Thalassemia. The first is Beta Thalassemia Minor. This is where at least 1 of the 2 genes is fully functional, represented as (B/B0) or (B/B+). This means one gene makes fully functional Beta globin proteins. These patients are typically mild in their anemia and symptoms. Patients with at least 1 partially functional gene will fall into Beta Thalassemia Intermedia. They will have moderate anemia and need some transfusions. This is represented by the possibilities of (B+/B+) or (B+/B0). The final category is the Beta Thalassemia Major patients. They have no functional copies of the Beta globin gene. They are (B0/B0). They will have severe anemia and life long transfusions.
This will be a microcytic anemia which has low Hematocrit and low Hemoglobin levels and low MCV. Beta Thalassemia patients will often have a higher than normal Red Blood cell count like 6 million or more per microliter. This is thought to occur as the body is producing huge amounts of RBCs to try to keep up. Without any functional Beta Globin, these RBCs will make Hemoglobin out of 4 alpha chains which will be unstable. These RBCs won't live very long. Any of the bad non functional Beta globin chains will still be in the RBCs and precipitate in the cells. This will cause the Spleen Macrophages to destroy these RBCs. This will lead to an enlarged spleen and Hemolytic anemia with high LDH and Bilirubin levels.
With Beta Thalassemia you can also see bone abnormalities as the bones around the skull and face grow larger bone marrow capacity to attempt to make more Red Blood Cells. You can also see what is called extramedullary hematopoiesis. This is where the stem cells that make all the cells of the blood spread out into the organs like the Spleen and Liver to start producing new Red Blood cells in those organs. This contributes to enlargement of both the spleen and liver. The only treatment for Beta Thalassemia is blood transfusions which brings with it the iron overload and the need for chelation therapy.
The same gene editing therapy they are using in Sickle Cell Disease is also being developed for Beta Thalassemia. They extract the stem cells from the patient and edit them to switch them back to making Fetal Hemoglobin. They will use Busulfan myeloablation therapy to wipe out the bad stem cells. Then they administer the edited stem cells which will make Fetal Hemoglobin. The data shows this is a functional cure for this disease.
Autoimmune Hemolytic Anemia
Up until now, we studied all the intrinsic defects of Red Blood cells. These all focused on something being wrong with the Red Blood cell itself like structural proteins, iron deficiency or defects in Hemoglobin formation. Now we are going to start looking at the extrinsic factors that can target and kill Red Blood Cells. This can be things like drugs that attach to Red Blood cells and cause antibody formation toward those drugs. This is the case in some forms of Penicillin reactions. Here the Penicillin binds to the RBC and then the immune system creates antibodies toward this new foreign substance that is bound to the RBC. Then the immune system kills the RBC as if it were a pathogen. This is the rare case of drug induced hemolytic anemia.
The most common case of Autoimmune driven anemia is acquired. This means it can happen to anyone at any time. This comes from antibodies being formed toward a pathogen that suddenly binds to proteins on the surface of the Red Blood cells. To understand this, I have to dive a bit into immunology, antibodies and Epitopes. I covered these concepts in the Immunology section. There are thousands of proteins made within the body. Even pathogens are made up of proteins. All these proteins are made up of amino acids. A protein is just a long string of amino acids folded into a 3 dimensional shape. The receptors of Antibodies and T cells will recognize a specific sequence of amino acids. For antibodies, it is 13 to 25 amino acids in size. Each Antibody only recognizes a specific sequence of amino acids of the much larger protein. Since proteins can be hundreds or even thousands of amino acids in length, there is a potential of antibodies to be made toward many parts of the protein. This could be a pathogen protein like a bacteria cell wall, or it could be the protein on one of our cells like CD19. Each antibody only recognizes a specific piece of that protein called the epitope. This leads us to the idea of a collision in the epitope of a protein with something bad like a bacteria and something good like a protein on the surface of a Red Blood Cell. There are only 20 amino acids and tens of thousands of proteins. The odds of 2 proteins having the same epitope for an antibody is bound to exist. This means the antibody you made for the flu last year might share an epitope with a protein on your RBCs.
Guillain barre syndrome is another autoimmune disorder that can appear shortly after a new infection as antibodies created start to attack nerve cells. This can also occur in cancer where antibodies toward the tumor will attack healthy tissues. This is called Paraneoplastic syndrome. These 2 diseases are acquired autoimmune disorders. They don't attack Red Blood cells, but they help demonstrate the idea that antibodies created toward a pathogen can have an epitope that matches something friendly. In Autoimmune Hemolytic Anemias (AIHA), you get antibodies for proteins on the Red Blood Cell. This means those antibodies will bind to the RBC and drive an immune response either by complement or by spleen macrophages. This leads to a destruction anemia as Red Blood cells are destroyed.
Lysis means the destruction of cells by the rupturing of the cell membrane. The term Hemolysis means the rupturing and destruction of Red Blood cells. This can occur in many anemias. We often call these the Hemolytic Anemias or the Destruction Anemias.
There are specific signs and symptoms seen with Hemolytic Anemias. First will be the signs and labs for anemia. You will see low Hematocrit, low Hemoglobin and low Red Blood Cell count (except Beta Thalassemia). The patient will be pale, tired and maybe have shortness of breath. There will be a high Reticulocyte count. If you recall, the reticulocyte count is the percentage of all RBCs that are new immature RBCs in circulation. If this number is below 1% you will think underproduction anemia. If the reticulocyte count is high, then you should consider a destruction anemia. A reticulocyte count of above 3% is an indicator that a ton of new RBCs are being made to keep up with the loss of RBCs in circulation.
The key labs for Hemolysis are elevated LDH, elevated unconjugated bilirubin and low haptoglobin. This is the common lab for showing red blood cell destruction. The LDH comes from a metabolism enzyme while bilirubin comes from breakdown of Heme. When Red Blood cells are destroyed in the circulation they can occur intravascular or extravascular. When you hear the term extravascular, you should always think spleen.
The RBCs must pass through the spleen where there are spleen macrophages that line the vessels. If there is any defect in these Red Blood cells, those spleen macrophages will engulf and break them down. This can be RBCs coated with antibodies due to an autoimmune reaction. It could also be RBCs that just have shape defects like Spherocytosis. It could also be RBCs with defects inside them like inclusion from hemoglobin clumping. Whatever the case is, any RBCs that don't pass strict inspection from spleen macrophages will be ingested and broken down. The iron will be recycled for new RBCs and the waste products like Bilirubin will be processed for waste in the liver.
Intravascular hemolysis occurs in the vessels. It has 3 causes with complement, mechanical and Microangiopathic Hemolytic Anemia (MAHA). The mechanical form comes from things like a heart pump or destruction of Sickle cells in the blockage of a vessel. The MAHA comes from destruction of RBCs by things other than the immune system. This is typically things like DIC, TTP, aHUS or HELLP syndrome. We will go over these later under platelets. The last one is the Autoimmune Hemolytic Anemia (AIHA). This is driven by antibodies binding to the RBCs and triggering complement proteins which leads to Lysis of the cells and destruction in the vessels. These hemolytic causes of anemia can cause enlarged spleen due to the extravascular destruction in the spleen or extramedullary RBC production in the spleen. It can also cause enlarged liver due to the high level of bilirubin processing for waste or extramedullary RBC production in the liver.
So by now you are thinking that both intravascular and extravascular hemolysis have all the same symptoms. How in the world will we know the difference? The answer is hemoglobinuria. This is what they call Tea Colored Urine. When RBCs are broken down in the spleen, the macrophages recycle the iron. When intravascular hemolysis occurs, all that hemoglobin is dumped into the blood. It gets carried out into the urine as waste. Iron is a dark brown colored element. This then turns the urine a brown like color. If you hear tea colored urine, you should think of intravascular hemolysis.
Warm vs Cold AIHA
First comes the name of this disease as it tells us a lot about what is happening. This Autoimmune which means it has the immune system responding to healthy tissues. It is a miss direction of the immune system toward Red Blood cells. It is Hemolytic which means the destruction of Red Blood cells by the immune system. This will bring with it all the classic hemolysis labs like elevated LDH, elevated unconjugated bilirubin, and low haptoglobin. That means enlarged spleen is most likely. We see anemia which means there will be low Hematocrit, low Hemoglobin and low RBC count. Put this all together and you get anemia caused by the destruction of RBCs by the immune system. This is an Antibody driven response.
This is broken down into 2 classes of AIHA with Warm and Cold. The Warm is directed by IgG and the cold is directed by IgM antibodies. This leads to different responses. These are given their names as the Cold form of AIHA actually responds to cold temperatures. AIHA is divided into 80% Warm and 20% Cold. The warm is directed by IgG antibodies binding to red blood cells. The IgG has low levels of complement fixation so you will see low levels of intravascular red cell destruction and high levels of extravascular destruction. This is where the spleen macrophages will engulf and destroy the red blood cells coated with the IgG antibodies. This means you will see little to no Hemoglobinuria and an enlarged spleen. Warm AIHA tends to be more emergent and severe than the Cold form of the disease. Even though it can be very severe, the long term survival with Warm AIHA is still very good with 70% surviving about 10 years.
The Cold form of AIHA activates in cold temperatures. It will sometimes have the effect of turning the fingers blue. This gives it its name Cold Agglutinin Disease. This is driven by IgM antibodies binding to the red blood cells. The IgM has a high activity for fixing complement which will lead to hemolysis of the red cells in the vessels. The IgM antibodies love to agglutinate which basically means they clump up. This causes the red cells to be destroyed in the vessels. This is often a milder form of AIHA which tends to be chronic in elderly people. It leads to intravascular hemolysis so hemoglobinuria may be in the labs.
The test for distinguishing AIHA from other forms of hemolytic anemias is a Direct Coombs test. This test will detect the self reactive antibodies. It can also tell if they are IgG or IgM antibodies. This is the one test that can separate AIHA from MAHA. Because this is the destruction of RBCs by antibodies, giving transfusions is not helpful. The antibodies would just kill the new RBCs. They are often treated with Immunosuppressive drugs like Prednisone. In more severe cases, they could use more extreme suppressive drugs like Rituximab which clears all the possible self reactive B cells. They might even use Fludarabine or Bendamustine.
Paroxysmal Nocturnal Hemoglobinuria
This is another hemolytic anemia that comes from immune destruction of the Red Blood cells. This is done by the complement system of the immune system. The complement is a group of about 9 proteins that circulate in the blood and activate when they come in contact with specific pathogens. I will save complement for immunology, but an understanding of the basics is necessary here. These proteins spring into action when they come in contact with pathogens in the blood. They become active and lead to coating of the pathogen with complement proteins. This can lead to inflammation and lysis (destruction) of the pathogen. The complement also works with antibodies by binding to them and activating the complement system. Our healthy cells have proteins on their surface called CD55 and CD59 which block the complement from binding to them. The disease of PNH comes when the stem cells in the bone marrow mutate and stop expressing these proteins that are designed to protect Red Blood Cells from the complement proteins. The Gene for CD55 and CD59 is called the PIGA gene. When there is a mutation in it, the proteins that are expressed on the surface of Red Blood cells like CD55 and CD59 will be missing. There is no protection for these RBCs from the complement. This leads to an intravascular destruction of the RBCs by the complement system. PNH is thus an acquired disease.
Paroxysmal means irregular and periodic. That means this disease comes in episodes. The second part is Nocturnal which means at night. That means these episodes often happen at night. This happens with hemoglobinuria in the morning or Tea colored urine. PNH is an anemia so you will see anemia with low Hematocrit, low Hemoglobin, and low RBC count. It will be hemolysis so have high reticulocyte count, high LDH, high unconjugated bilirubin and low haptoglobin. It will be intravascular as that is where the complement proteins exist. This means it will look very much like Autoimmune hemolytic anemia. There are a few big things that will help distinguish them apart.
The Coombs test will be negative in PNH as it is not driven by antibodies. There will often be a pan cytopenia with low platelet and white blood cells along with the anemia. PNH also has blood clotting which can end up being life threatening. They often require blood thinners. The go to treatment for PNH is Eculizumab which is a C5 complement inhibitor. This disease is estimated to affect between .5 and 1.5 people per 1 million population which makes it very rare. It is estimated that between 5,000 and 6,000 patients are living with PNH in the US.
* I am not a doctor. This is not designed to be Medical Advice. Please refer to your doctor for Medical Decisions