Hemoglobinopathy Profile

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A sickle cell test looks for the presence or absence of abnormal hemoglobin in the blood that causes sickle cell anemia.
This test is done to tell if you have abnormal hemoglobin that causes sickle cell disorder and sickle cell trait.
In sickle cell disorder, a person has two abnormal hemoglobin S genes.
A person with sickle cell trait has only one of the problem hemoglobin S genes and no symptoms, or only mild ones.
However, this test does not tell the difference between these two conditions. Another test called hemoglobin electrophoresis is needed to do so.

Sickle cell tests are used to detect, diagnose, and confirm sickle cell anemia (also called sickle cell disorder) and to identify those who may have sickle cell trait. Sickle cell anemia is an inherited disease that leads to the production of an abnormal hemoglobin called hemoglobin S (Hb S or Hgb S). Hemoglobin is a protein found in red blood cells (RBCs) that binds to oxygen in the lungs and carries it to tissues throughout the body.
Typically, hemoglobin A (Hb A) makes up most of the hemoglobin found in normal RBCs in adults, with small amounts of hemoglobin A2 and hemoglobin F. Before babies are born, they normally produce large amounts of hemoglobin F (Hb F), which is then slowly replaced by Hb A after birth. Mutations in the genes that code for the production of hemoglobin can lead to abnormal types of hemoglobin. Common mutations include beta thalassemia and those associated with hemoglobin variants such as Hb S, hemoglobin C (Hb C). With a normal hemoglobin gene copy from one parent and a Hb S gene copy from the other parent (heterozygous), a person is said to have sickle cell trait and be a sickle cell carrier. When a person has two Hb S gene copies (one from each parent; homozygous), then he has sickle cell anemia (disorder). If he has one Hb S gene and one other abnormal gene, such as Hb C gene, then he will experience some of the same symptoms associated with sickle cell disorder.
Hb S can form crystals that change the shape of the RBC from a round disc to a characteristic sickle shape. This altered shape limits the RBC's ability to flow smoothly throughout the blood vessels in the body, limits the hemoglobin's ability to transport oxygen to tissues, and decreases the RBCs' lifespan from 120 days to about 10-20 days. A person with sickle cell disorder (homozygous for Hb S) can become severely anemic because the body cannot produce RBCs as fast as they are destroyed. The affected person can suffer painful episodes and a variety of complications when sickled cells become lodged in and obstruct small blood vessels.
Sickle cell tests are done to determine whether someone is producing hemoglobin S, thus carrying a sickle gene. They are ordered routinely as part of newborn screening programs and are mandated by every state in the US and the District of Columbia. If results of a newborn screen are abnormal, then one or more sickle cell tests may be ordered to confirm abnormal findings. Sickle cell tests may also be ordered along with or following an abnormal CBC and blood smear, with normal iron studies to help evaluate a patient who has an unexplained hemolytic anemia or demonstrate symptoms that suggest the presence of sickle cell anemia.

Sickle cell tests are used to identify the presence of hemoglobin S, to evaluate the status and number of the person's RBCs and hemoglobin level, and/or to determine whether a person has one or more altered hemoglobin gene copy. The presence of other abnormal hemoglobin variants may be seen but would require additional testing to identify specifically what type.
There are almost 900 hemoglobin variants of which hemoglobin S is one. To screen for and to confirm the presence of hemoglobin S, a variety of tests have been developed. Some of these may include:
For Screening:
Screening may be performed on family members of an individual who has proven to have sickle cell trait/disorder. It also may be done for those who were not screened at birth because universal testing was not yet implemented and who may choose to be tested if their status is not known.
·Hemoglobin S solubility test and Sodium Metabisulfite Test. Both tests are used in screening for hemoglobin S by adding certain chemicals to the patient's blood sample that reduce the amount of oxygen present. In those who carry one sickle cell gene (sickle cell trait), some hemoglobin S will be present. The reduced amount of oxygen will cause the abnormal sickle cells to form. This test detects the presence of hemoglobin S but does not distinguish between sickle cell disorder and trait. It should not be performed on infants until they are at least 6 months old because of the presence of hemoglobin F at birth. Infants with sickle cell disorder or trait will not produce significant amounts of hemoglobin S until several months after birth; thus this test may give a false negative result if performed too early (if hemoglobin S is <10%).  
For Screening, Diagnosis, and Confirmation:
·Hemoglobinopathy (Hb) evaluation. There are several methods of evaluating the type and relative amounts of various normal and abnormal hemoglobin types. These methods typically separate the different types of hemoglobin that are present so that they can be identified and quantified. They include:  
·Hemoglobin electrophoresis has been traditionally used as the method to identify the presence of various hemoglobins.  
·Hemoglobin fractionation by HPLC is the most often used method for screening for hemoglobin variants, including Hb S.  
·Isoelectric focusing is also a highly sensitive method that is often used.  
·Newborn screening for sickle cell is now mandated by all 50 states in the U.S. and the District of Columbia. It is performed via the more sensitive Hb isoelectric focusing or HPLC fractionation and identifies the specific types of hemoglobin present. As an infant with sickle cell trait/disorder grows and develops, the amount of Hb S will increase as the amount of hemoglobin F decreases. At about age 2, the levels stabilize.  
·DNA analysis. This test is used to investigate alterations and mutations in the genes that produce hemoglobin components. It may be performed to determine whether someone has one or two copies of the Hb S mutation or has two different gene mutations. Genetic testing is most often used for prenatal testing: amniotic fluid may be tested at 14 to 16 weeks to provide a definitive answer. Genetic counseling is strongly encouraged if a positive sickle screen from one or both parents is determined. It can also be performed earlier with chorionic villus sampling.  
For monitoring treatment:
Particularly in patients with sickle cell disorder, the amount of Hb S will be measured and followed over the course of a treatment, for example, after a blood transfusion to ensure that the hemoglobin S level has been reduced.
Other tests that may be used to help evaluate someone who is suspected of having or who is known to have sickle cell trait or disorder include:
·Complete blood count (CBC). The CBC is a snapshot of the number of cells in the bloodstream. Among other things, the CBC will tell the doctor how many red blood cells are present and how much hemoglobin is in them, and will evaluate the size and shape of the red blood cells present. This test is used to detect anemia.  
·Blood smear (also called peripheral smear and manual differential). In this test, a trained laboratorian looks at a thin stained layer of blood on a slide under a microscope. The number and type red blood cells are evaluated to see if they are normal. Sickled cells and cell fragments can be seen on the blood smear.  
·Iron studies. These may include: iron, ferritin, UIBC, TIBC, and transferrin saturation. These tests measure different aspects of the body's iron storage and usage. They are ordered to help determine whether the patient has an iron deficiency anemia or an excess amount of iron. People with sickle cell anemia who receive multiple blood transfusions may experience an iron overload.  

Sickle cell tests are routinely ordered to screen newborns for sickle cell anemia. All 50 states in the US and the District of Columbia now require screening for all newborns.
Testing may be done when those who were born before newborn screening was mandated want to know if they have sickle cell disorder or are carrying the sickle cell trait, especially if they are in a high-risk group. It has been estimated that 1 out of every 500 African-Americans has sickle cell anemia.
One or more sickle cell tests may be done to help diagnose someone who has not previously been tested when they have symptoms and/or complications of the disorder such as:
·Pain due to sickle cell crises - the most common symptoms of sickle cell disorder are episodes of pain that can last for extended periods of time. The pain can occur throughout the body and often involves the bones, joints, lungs, and stomach.  
·Anemia - sickle cell disorder is a hemolytic anemia, meaning that the abnormal, sickled RBCs break down (hemolyze) more quickly than normal red blood cells and can not be replaced by the body as quickly as needed, thus leading to a decreased number of RBCs and reduced ability of the RBCs to transport oxygen throughout the body.  
·Increased number and frequency of infections, especially pneumonia in children.  
·Coughing, chest pain, and fever suspected to be caused by a serious complication of sickle cell disorder called acute chest syndrome.  

Test results
Newborn screening
In newborns who carry the sickle cell gene, fetal hemoglobin F will predominate, but a small amount of hemoglobin S will also be present. There also may be a small amount of hemoglobin A if they have sickle cell trait. A full work-up should be done after the child reaches six months of age.
Diagnostic testing
Adults with sickle cell trait will produce mostly normal hemoglobin A, while those with sickle cell disorder (anemia) will produce mostly Hb S with little or no Hb A. People who are heterozygous for two different hemoglobin variants will usually produce varying amounts of both types. For example, they may produce both Hb S and Hb C.
Genetic testing
If two copies of the Hb S gene mutation are detected, then the person has sickle cell disorder. If they have one gene that codes for Hb S and one normal gene, then they have sickle cell trait. If they have one Hb S copy and a Hb C or beta thalassemia mutation, then they are likely to experience some symptoms and complications associated with sickle cell disorder. If they have one Hb S gene copy and another, rarer hemoglobin variant, then they may or may not have any symptoms or complications. See the article on Hemoglobin Variants for more on this.

Also you should know
Sickle cell anemia symptoms and the complications experienced will vary greatly from person to person even within the same family.
Recent blood transfusions may affect results.
People with sickle cell trait are generally healthy, but those who exercise heavily, such as athletes and those who are exposed to dehydration or altitude extremes, may sometimes experience sickle cell anemia symptoms. Sickle cell carriers produce both Hb A and some Hb S. When they are subjected to significant stresses that produce reduced oxygen in the body, the RBCs that contain Hb S can sickle.
Anyone can inherit Hb S gene mutationsm but sickle cell disorder is more prevalent among those of African ancestry and those who can trace their roots to the Mediterranean area, South and Central America, the Middle East, India, and the Caribbean.
It mirrors the areas of the world where malaria is found. Historically, sickle cell offered some protection and survival advantage against malaria. Since people from these areas have moved throughout the world, sickle cell gene mutations have become widespread.
Newborn screening identifies most cases of sickle cell trait and sickle cell anemia. However, this screening was not universally performed in the U.S. until relatively recently. Many adults, and especially athletes born in other countries, may not have been tested to determine their sickle cell status. Since there is some risk of "exertional sickling" during intense training, the National Collegiate Athletic Association (NCAA) advocates testing college athletes who have not documented their sickle cell status.

All information on this page is intended for your general knowledge only and does not provide medical advice, diagnosis or treatment.