Gold-standard test to diagnose Sickle Cell Anemia

1.

Elsevier ClinicalKey Clinical Overview

Diagnosis Suspect diagnosis based on known family history, results of prenatal testing or newborn screening, or presence of clinical manifestations in a person of sub-Saharan African, Middle Eastern, Mediterranean, Indian, Caribbean, or Central or South American descent Diagnosis is established by hemoglobin analysis using protein-based methods (eg, protein electrophoresis, high-performance liquid chromatography, isoelectric focusing) or molecular methods (DNA testing) CBC and peripheral blood smear show characteristic sickle cells and evidence of hemolytic anemia Other routine tests after initial diagnosis include assessment of iron status, renal and liver function tests, and extended red cell phenotyping Additional laboratory tests, imaging, and other evaluations may be indicated to assess for specific complications depending on clinical context

Diagnosis CBC with differential Shows normocytic anemia in hemoglobin SS disease and microcytic anemia in other forms of sickle cell disease Hemoglobin levels vary 6 to 9 g/dL in hemoglobin SS disease 7 to 9 g/dL in hemoglobin Sβ⁰-thalassemia 9 to 12 g/dL in hemoglobin Sβ⁺-thalassemia 9 to 14 g/dL in hemoglobin SC disease Elevated reticulocyte count is suggestive of hemolysis Peripheral blood smear Shows sickle cells, nucleated RBCs, target cells, and other abnormal RBCs Hemoglobin SS disease is characterized by predominant sickle cells with a few target cells Hemoglobin Sβ-thalassemia is characterized by target cells, sickle cells, and hypochromic microcytic discocytes Hemoglobin SC disease shows predominant target cells with rare sickle cells L-lactate dehydrogenase Elevated levels indicate hemolysis Hemoglobin analysis Establishes diagnosis of sickle cell anemia and excludes other hemoglobinopathies Hemoglobin assay demonstrating HbS in conjunction with absent or diminished amount of adult hemoglobin is diagnostic Methods include high-performance liquid chromatography, isoelectric focusing, cellulose acetate electrophoresis, and citrate agar electrophoresis Typical findings in adults and children (not neonates) are available from the National Heart, Lung, and Blood Institute Newborn screening programs test blood obtained by heel prick using isoelectric focusing or high-performance liquid chromatography Fetal hemoglobin is usually predominant hemoglobin in newborns and levels decrease over course of first year of life Normal newborn screening result shows more fetal hemoglobin compared with adult hemoglobin

Synopsis Diagnosis is established by hemoglobin analysis using protein-based or molecular methods, CBC, and peripheral blood smear demonstrating characteristic sickle cells and evidence of hemolytic anemia Management consists of preventing invasive pneumococcal disease in childhood, hydroxyurea therapy or blood transfusion to ameliorate or prevent manifestations of sickle cell disease, control of symptoms (eg, pain), and surveillance for chronic organ damage Hemopoietic stem cell transplantation can be curative in patients with sickle cell anemia

2.

Elsevier ClinicalKey Clinical Overview

Diagnosis Presence of sickle cells suggests sickle cell anemia, which should be verified by hemoglobin electrophoresis Elliptocytosis constituting 25% or more of the RBC population is characteristic of hereditary elliptocytosis Bite cells or Heinz bodies are occasionally seen in glucose-6-phosphate dehydrogenase deficiency Normal or nondiagnostic RBC morphology in the setting of hemolysis suggests an RBC enzyme defect (eg, glucose-6-phosphate dehydrogenase deficiency, pyruvate kinase deficiency) or paroxysmal hemoglobinuria Further testing might include glucose-6-phosphate dehydrogenase and/or pyruvate kinase enzyme assays flow cytometry Appearance of erythroblasts and teardrop cells suggests bone marrow failure or infiltration and need for a bone marrow biopsy Intracellular parasites (eg, malaria, babesiosis) may be observed, but special staining should be requested if these are suspected Abnormalities in WBC and/or platelet morphology, cytopenias, or presence of immature forms may suggest a primary marrow disorder (including hematologic malignancy) and may necessitate a bone marrow biopsy or other evaluations Not uncommonly, multiple concurrent processes exist and may confound interpretation of test results (eg, chronic inflammation plus nutritional deficiency) Further studies may be indicated on basis of clinical presentation and results of preliminary testing (eg, viral studies, rheumatologic testing, imaging) In urgent cases that require transfusion before work-up, it is important to draw and hold blood for later testing because transfusion can alter results

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Howard, Jo (2024). In Goldman-Cecil Medicine (pp. 1109). DOI: 10.1016/B978-0-323-93038-3.00149-0

• The sickle solubility test will detect sickling of hemoglobin in solution by treatment with a reducing agent. It is specific for sickle hemoglobin but does not differentiate among HbAS, HbSS, and other compound heterozygotes of sickle cell hemoglobin. • Hemoglobin electrophoresis was the first method used to demonstrate hemoglobin variants but is time-consuming and labor-intensive. • DNA sequence analysis identifies the specific globin gene mutation (seeFig. 149-3C). • Tandem mass spectrometry identifies the specific amino acid change in the globin chain.

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Christopher H, Burns A, Josephat E, et al. BMC Genomics. 2021;22(1):902. doi:10.1186/s12864-021-08220-x. Copyright License: CC BY

Publish date: December 4, 2021.

RESULTS: Sequencing results for SCD using the MinION were 100% concordant with those from the Sanger method. In addition, the long-read DNA sequencing method enabled the resolution of cases with unusual phenotypes which make up 1% of all children in Tanzania. The cost is £11/ sample for consumables, which is cheaper compared to other sequencing platforms. CONCLUSIONS: This is the first report of a comprehensive single DNA assay as a definitive diagnostic test for SCD and other haemoglobinopathies. The test is fast, precise, accurate and affordable.