Sickle cell disease (SCD) comprises a group of inherited blood disorders in which alterations in the structure of hemoglobin result in the sickling and early death of red blood cells. The result is inefficient transportation of oxygen to the tissues. The abnormally shaped red cells also obstruct small blood vessels, causing pain and sometimes stroke.1 Show Genetic TestingIn the United States, newborn screening via DNA analysis for the early detection, monitoring, and prompt treatment of SCD is mandatory.2 A prenatal diagnosis of SCD can be obtained early via chorionic villus sampling or later, between weeks 14 and 16, through amniotic fluid testing.2,3 Before pregnancy, women may undergo genetic carrier testing and genetic counseling so that they understand the risks of passing SCD along to their children.3 The identification of less common variants of SCD may require specialized DNA sequencing.3 Blood TestsBlood tests are part of the preliminary evaluation for SCD. Common hematologic abnormalities in patients with SCD include elevated levels of platelets, leukocytes (primarily neutrophils; cell count between 12,000 and 20,000/mm3), and often reticulocytes. Laboratory tests also show decreases in the hemoglobin level (5-9 g/dL), hematocrit (17%-29%), and erythrocyte sedimentation rate.4 Peripheral blood smears reveal the characteristic elongation and sickling of red blood cells. The patient may be asplenic if red blood cells with Howell-Jolly bodies (nuclear remnants) are present.4 Although they are not diagnostic, the hemoglobin S (HbS) solubility test and sodium metabisulfite test may identify HbS in children older than 6 months. The tests do not differentiate between those with SCD and those with sickle cell trait (SCT).3 In hemoglobin electrophoresis, an electric current is used to identify and measure the different types of hemoglobin in the blood. The presence of abnormal hemoglobin (HbS, HbC, or HbE) may indicate sickle cell disease or anemia.5 In addition to hemoglobin electrophoresis, other tests used to evaluate for a hemoglobinopathy include isoelectric focusing, hemoglobin fractionation by high-pressure liquid chromatography (HPLC), mass spectrometry, and capillary zone electrophoresis.3 Iron studies measuring the body’s ability to store and use iron can detect either iron deficiency anemia or iron overload in patients who require multiple blood transfusions.3 Children younger than 5 years of age with fever should undergo urinalysis, blood cultures, liver function tests, and a complete blood cell (CBC) count, including a differential and reticulocyte count. A significant drop in the hemoglobin level of more than 2 g/dL suggests a hematologic crisis, which may require a blood transfusion. Before a transfusion, a blood type and crossmatch test is required to ensure that the donor blood is compatible with the patient’s blood.6 Although the leukocyte level is usually elevated in individuals with SCD, major elevation to above 20,000/mm3 indicates possible infection. A decrease in the leukocyte level is associated with a possible parvovirus infection. Numerous factors influence the reticulocyte count, an indicator of bone marrow responsiveness. The reticulocyte count in splenic sequestration is normal. Aplastic crisis and hyperhemolytic crisis cause low and high reticulocyte counts, respectively.6 Additional TestingOther potentially useful laboratory tests include serum electrolyte, serum creatinine, and blood urea nitrogen measurements; a lactic dehydrogenase assay; and a haptoglobin assay. Although the 2 assays are not mandatory, increased LDH and decreased haptoglobin can indicate the presence of hemolysis.7 Urinalysis in a patient with SCD commonly reveals hematuria and isosthenuria but may also identify a urinary tract infection that requires treatment.7 In individuals without a diagnosis, a sickling test can confirm the presence of an abnormal beta-globin gene. In individuals with a diagnosis, arterial blood gas measurements indicate the severity of a respiratory crisis. Additionally, an elevated level of secretory phospholipase A2, an enzyme that metabolizes triglycerides by removing fatty acids, is a clinical biomarker of acute chest syndrome during a pain crisis.7 Chest radiography may assist in diagnosing SCD in patients experiencing acute respiratory distress. Plain radiography may help in the evaluation of bone infarction, osteonecrosis, and advanced osteomyelitis.8 Magnetic resonance imaging (MRI) may detect avascular necrosis, marrow hyperplasia, early signs of osteonecrosis, osteomyelitis, bony infarction, and cerebral infarction in patients with SCD.9 Computed tomography (CT) is used to rule out renal medullary carcinoma in patients with SCD who present with hematuria. CT may also be helpful in detecting subtle changes of osteonecrosis in patients who cannot undergo MRI.9 Nuclear medicine is a cost-effective way to detect the initial stages of osteonecrosis (technetium 99m bone scanning) and osteomyelitis (indium 111 white blood cell scanning).10 Transcranial Doppler ultrasonography (TCD) may be used to analyze blood flow velocity within the circle of Willis. Children with SCD whose blood flow velocity is relatively high are at increased risk for stroke. Children in whom sickle cell anemia (HbSS) or sickle-beta zero thalassemia has been diagnosed between the ages of 2 and 16 years should be screened with TCD annually if the results continue to be normal, every 4 months if the results are marginal, and within 2 to 4 weeks if the results are abnormal.11 Abdominal ultrasonography can be performed to measure the size of the liver and spleen and to detect cholecystitis, cholelithiasis, nephrolithiasis, ectopic pregnancy, and papillary necrosis in the kidneys.12 Echocardiography can rule out left ventricular diastolic dysfunction, which correlates with premature death in patients with SCD. It also identifies tricuspid regurgitation and pulmonary hypertension in these patients. Patients with SCD who have respiratory problems should undergo echocardiography. The ability of echocardiography to detect early-stage high-output heart failure is limited when a patient is evaluated at rest; therefore, low-level invasive exercise testing is recommended when heart failure is suspected in a patient with SCD whose echocardiographic results are inconclusive.13 References
Reviewed by Kyle Habet, MD, on 11/30/2021. Regular blood work is an important way to track overall health. It is especially important for people with blood disorders like sickle cell disease (SCD). Blood tests during routine doctors visits can give information about the status of the disease and screen for complications. Some common routine blood tests are complete blood count (CBC) and reticulocyte count, which tell doctors about different types of blood cells. Blood tests for kidney and liver function are also common. These tests are often performed together on a comprehensive metabolic panel of tests that also includes measurements of electrolytes, proteins, and glucose in the blood.1-3 During the test, doctors will draw blood from a needle inserted into a vein in your arm or hand. They will analyze it in a lab and discuss the results with you. Follow your doctor’s instructions about preparing for the test. What is a complete blood count?A complete blood count (CBC) is usually performed at every doctor’s visit for people with SCD. It gives doctors information about all 3 types of blood cells: red blood cells, platelets, and white blood cells. SCD mainly affects red blood cells, but can sometimes modify platelets and white blood cells. Some SCD medications also affect blood cells.4,5 People with SCD generally have anemia (fewer red blood cells than normal) because sickled red blood cells do not circulate in the blood as long as normal red blood cells. This leads to lower hemoglobin levels as well. A normal hemoglobin level is around 12 to 15 g/dL. People with SCD have hemoglobin levels of 6 to 11 g/dL.4,5 People with SCD usually have higher levels of white blood cells, especially neutrophils. These are a type of white blood cells that fight bacterial infections. Major increases in white blood cell count may indicate infections. On the other hand, people taking hydroxyurea may have too few neutrophils to fight off infections (neutropenia).4,5 The exact levels of each blood cell depend on the type of SCD and the person. It is important for your doctor to know your normal hemoglobin level. A major change from your normal levels may indicate an acute complication, such as severe anemia.4-6 What is a reticulocyte count?Reticulocytes are young, immature red blood cells forming in the bone marrow (the soft center of bones). Normally, reticulocytes are only released into the blood after they develop into red blood cells. For most healthy people, the number of reticulocytes in the blood is very low. A normal reticulocyte count is 0.45 to 1.8 percent.5 People with SCD have more reticulocytes in the blood because the body is rapidly making more red blood cells to offset anemia and releasing the reticulocytes early. People with SCD may have a reticulocyte count of 2 to 3 percent or more.5 What tests are done to check kidney function?Kidney disease is a common complication of SCD. When sickle cells block blood flow to the kidney, it can no longer filter out waste properly.7,8 Children and adults with SCD should get regular blood tests for kidney function. Common blood tests measure the amount of creatinine or blood urea nitrogen (BUN) in your blood. Creatinine is a waste product released directly into the urine by the kidneys. Urea is a waste product formed when proteins are metabolized.9,10 High blood creatinine or BUN levels may mean that your kidneys are not working as well as they should. A BUN-to-creatinine ratio may also be used to diagnose kidney problems.9,10 What blood tests are done to test liver function?Liver problems are also common for people with SCD. Sickle cells can block blood flow to the liver and prevent it from getting rid of waste. Chronic blood transfusions also increase the risk for liver damage.11 People with SCD should get regular blood and other tests for liver function. Common blood tests measure the amount of bilirubin, aspartate transaminase (AST), and alanine aminotransferase (ALT).12,13 Bilirubin is a yellow pigment produced during the normal breakdown of hemoglobin and is processed by the liver. High bilirubin levels may indicate liver disease, gallstones, or hepatitis, depending on the type of bilirubin. ALT and AST are enzymes in the liver that gets released into the blood when the liver is damaged.12,13 What other blood work do people with sickle cell disease get?Other blood tests can give doctors information about the status of the disease. For example, some additional tests that doctors commonly perform include:2-3,14-15
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What labs are elevated in sickle cell crisis?
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