Sickle cell anemia Diagnosis

  • Diagnosis

    Sickle cell anemia is a type of anemia named after a characteristic change in shape that occurs in the red blood cells Figure 01. Anemia is a condition in which people do not have enough red blood cells. Red blood cells carry oxygen to body tissues with the help of a protein called hemoglobin. Normal red blood cells are circular, like a doughnut, and flexible. The cells of patients with sickle cell anemia have high levels of an abnormal type of hemoglobin called hemoglobin S. Hemoglobin S causes red blood cells to stiffen into a sickle shape, which looks like a crescent moon. Sickled cells die in about 10 to 20 days, compared to 120 days for normal red blood cells. Anemia develops because the body can't replace the dying cells fast enough.

    Sickle cell anemia is an inherited disease. To develop sickle cell anemia, a person must receive sickle cell genes from both parents. People who inherit a sickle cell gene from one parent and a normal gene from the other will have sickle cell trait. People with sickle cell trait generally do not have symptoms, but can pass the defective gene on to offspring. If each parent has a sickle cell gene, their children have a 25% chance of having sickle cell anemia and a 50% chance of having sickle cell trait.

    Millions of people worldwide suffer from sickle cell anemia; in the US, about 72,000 people have sickle cell anemia, and about 2 million have sickle cell trait.

    A sickle cell crisis is an episode of pain that occurs when cells do not get needed oxygen. Patients with sickle cell anemia do not have enough red blood cells to carry sufficient amounts of oxygen to the body. Sickle cell crises are characterized by severe pain, and frequently require medical treatment. Patients with sickle cell trait do not usually develop sickle cell crisis. However, they may first become aware that they are carriers if they develop stress or another illness that is accompanied by pain severe enough to require a doctor's attention.

    Click to enlarge: Sickled Cells

    Figure 01. Sickled Cells

    Sickle cell anemia is an inherited genetic disease, requiring a sickle cell gene from each parent. If both parents carry a defective gene for sickle cell anemia, each child they produce has a 25% chance of having the disease and a 50% chance of having sickle cell gene, or trait. People with sickle cell trait have only one sickle cell gene, and usually do not have symptoms. However, they can pass the trait to their children. Some patients inherit one sickle cell gene and another abnormal hemoglobin gene. These people may have symptoms similar to those who inherited two sickle cell genes.

    Dehydration, cold temperatures, infections, low oxygen levels, excessive alcohol intake, stress, and pregnancy may lead to a sickle cell crisis.

    Sickle cell anemia can cause many symptoms and life-threatening complications, including blocked blood vessels, worsening anemia, and serious infections Table 01. Patients with sickle cell anemia often have episodes of pain. Sickle-shaped cells stick to the walls of small blood vessels and have difficulty passing through them. The misshapen cells can clog the blood vessels, keeping needed oxygen from reaching the surrounding tissues. The blockages and resulting lack of blood supply can damage vital organs, such as the lungs, bones, liver, and kidneys. Clogging of the small vessels in the eye can deprive the part of the eye that receives and processes light (the retina) of needed nutrients, and can lead to blindness. In men, the penis may become painfully erect, a condition called priapism. Leg ulcers may occur when small vessels become blocked. Patients with sickle cell anemia are prone to gallbladder disease, and may develop bone complications when bone cells don't receive needed oxygen and nourishment. Children with sickle cell anemia are prone to strokes, which can cause permanent disabilities. Strokes occur when the sickled cells block or narrow the diameter of blood vessels that supply the brain with oxygen. Hand/foot syndrome occurs when small blood vessels in the hands or feet become blocked, resulting in pain, swelling, and sometimes fever.

    Table 1.  Symtoms and Complications of Sickle Cell Anemia

    Symptoms in adults and children
    Anemia
    Fatigue
    Frequent infections
    Painful joints and bones
    Acute chest or abdominal pain
    Slow growth
    Leg ulcers
    Stroke
    Symptoms in infants
    Fever
    Jaundice
    Swollen extremities and joints
    Pneumonia

    Patients with chronic anemia feel tired, their fingernail beds and mucous membranes become pale, and their skin may have a grayish tint.

    Pain is a primary symptom of sickle cell anemia in adults and children. Pain occurs during a sickle cell crisis because blocked blood vessels keep necessary oxygen from tissue cells, in effect “starving” them. Ninety percent of patients receiving hospital care for sickle cell disease experience severe pain in the bones, joints, or muscles. The pain may occur in the chest, back, abdomen, arms, or legs. Patients may have pain in one or more areas at once. Extremity pain usually occurs in both arms or both legs. Symptoms of a crisis can be mild or severe, and the pain may last for a few hours or for several weeks. Patients may have as few as 1 episode or as many as 15 or more episodes per year. Pain tends to occur in the same areas during subsequent crises.

    Fainting, light-headedness, or increasing fatigue may be the first sign of an acute episode of suddenly worsening anemia (a sequestration crisis). A sequestration crisis is a serious type of sickle cell episode during which huge numbers of red blood cells collect in the spleen. Anemia worsens due to the decrease in circulating red blood cells. The spleen normally helps the immune system fight disease-causing infections. Since most adults with sickle cell anemia no longer have functioning spleens, sequestration crises are more common in children. Patients who have sickle cell anemia and damaged spleens often develop serious infections because their bodies cannot mount an adequate defense against bacteria, viruses, and other invaders. Infection is a leading cause of death in children with sickle cell anemia.

    Patients may develop jaundice (characterized by a yellowing of the whites of the eyes) as a result of liver malfunction and rapid breakdown of red blood cells.

    Fever, cough, rash, headache, neck stiffness, or difficulty breathing or urinating may indicate an infection.

    Patients may experience depression or anxiety. Repeated painful, life-threatening, or incurable conditions often lead to feelings of hopelessness, helplessness, or anxiety. Frequent pain crises can be especially discouraging.

    People with sickle cell trait (one abnormal gene) do not usually have symptoms, but may develop pain and other problems under certain circumstances. Stress, infections, or a lack of oxygen may trigger a painful episode in people with sickle cell trait. People with sickle cell trait may also develop blood in the urine, and may be prone to kidney infections.

    Due to a lack of sufficient circulating red blood cells, adults with sickle cell anemia tend to be short, and children with sickle cell anemia may grow slowly and enter puberty later than their peers.

    Sickle cell anemia occurs predominantly in people of African descent, but also occurs in people from Mediterranean, Indian, and Middle Eastern descent. Thousands of years ago in this region of the world, a malaria epidemic killed many inhabitants. Some people survived the epidemic because they carried a single sickle cell mutation that made them immune to malaria. The survivors passed the defective gene to their children, and as people moved to other parts of the world, the genetic mutation spread.

    In the US, African-Americans, Native Americans, and Hispanics from the Caribbean, Central America, and parts of South America are more likely than other Americans to have sickle cell anemia. One in 375 African-Americans, 1 in 3,000 Native Americans, 1 in 20,000 Hispanics, and 1 in 60,000 whites are born with sickle cell disease. Eight percent to twelve percent of African-Americans have sickle cell trait.

    Various factors can trigger a painful sickle cell crisis. Sickle cell crises can be triggered by any event that decreases blood circulation or reduces the amount of oxygen in the blood. Low oxygen levels, cold temperatures, dehydration, infection, drinking large amounts of alcohol, stress, and pregnancy can lead to a crisis. Dehydration is especially common inpatients with sickle cell anemia because their kidneys are unable to properly conserve water.

    Blood tests can determine whether a person has sickle cell anemia. There are three main types of sickle cell disease: sickle cell anemia, sickle cell C disease, and sickle cell-thalassemia disease. Of these three, sickle cell anemia is the most common. The disease a patient has depends on the abnormal hemoglobin in his or her body. A blood test called hemoglobin electrophoresis helps determine whether abnormal hemoglobin is present and helps pinpoint its type. If no abnormal hemoglobin is found, it is unlikely that the patient has sickle cell anemia.

    Doctors will obtain a complete history and conduct a thorough physical examination to check for signs of anemia and complications, and to rule out other conditions that can cause similar symptoms. An increased heart rate can be a sign of pneumonia, heart problems, or a sequestration crisis. Low blood pressure may indicate shock from a body-wide (systemic) infection or a sudden worsening of anemia during a sequestration crisis.

    Doctors may order x-rays, ultrasonography, and other tests, depending on the patient's symptoms. Chest x-rays may be ordered for patients reporting chest pain or breathing problems. Doctors may order bone x-rays or scans for patients who have bone pain or symptoms indicating a bone problem. Ultrasonography of the abdomen can help identify possible causes of abdominal pain, and can determine the size of the liver and spleen. Tests called computed tomography (CT) and magnetic resonance imaging (MRI) may be helpful in evaluating the causes of neurologic symptoms, and in determining whether a stroke has occurred. A special type of ultrasonography (transcranial Doppler ultrasonography) may be used to determine blood flow when sickle cell disease is suspected of blocking vessels in the brain.

    Many babies in the US are tested for sickle cell anemia at birth, before they develop symptoms, so that doctors can start early treatment to prevent infections. Routine screening for sickle cell anemia is required in 40 states in the US. Symptoms of the disease rarely occur before infants reach four or five months of age because babies continue to produce increased amounts of fetal hemoglobin until then. Cells that contain fetal hemoglobin are less likely to become sickle-shaped and are more likely to function as normal cells.

    Sickle cell trait may be identified during a routine medical workup, during genetic counseling, or if a patient develops complications.

    Genetic counseling helps people who are thinking about starting a family learn about the chances of passing the disease to offspring. People with sickle cell trait are considered to be carriers. Even if they have no symptoms, they can pass the trait on to a child. Genetic counseling can help people make informed decisions about the risks involved in conceiving a child. If both parents have sickle cell trait, they have a 25% chance of producing a child with the disease, a 50% chance of having a child with the trait, and a 25% chance that a child will not have the trait or the disease.

    Before a baby's birth, doctors can test a sample of amniotic fluid (which surrounds the fetus) or tissue from the placenta to determine whether sickle cell anemia is present.

    Newborn babies at risk for sickle cell anemia should be tested so that they can receive earlier treatment, including antibiotics to protect against infections.

  • Prevention and Screening

    Genetic counseling helps people who are thinking about starting a family learn about the chances of passing the disease to offspring. People with sickle cell trait are considered to be carriers. Even if they have no symptoms, they can pass the trait on to a child. Genetic counseling can help people make informed decisions about the risks involved in conceiving a child. If both parents have sickle cell trait, they have a 25% chance of producing a child with the disease, a 50% chance of having a child with the trait, and a 25% chance that a child will not have the trait or the disease.

    Before a baby's birth, doctors can test a sample of amniotic fluid (which surrounds the fetus) or tissue from the placenta to determine whether sickle cell anemia is present.

    Newborn babies at risk for sickle cell anemia should be tested so that they can receive earlier treatment, including antibiotics to protect against infections.

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