sickle cell test(redirected from S test)
sick·le cell test
in an anaerobic wet preparation containing equal amounts of blood and 2% sodium bisulfite, erythrocytes containing hemoglobin S undergo a change in shape to a sickle-cell form; the number of sickled red blood cells per 1000 red blood cells is determined and expressed as a percentage.
sickle cell testA qualitative screening test for sickling haemoglobins, especially HbS. In the SCT, sodium metabisulfite or sodium dithionate is used to desolubilise haemoglobin S to the crystallised deoxygenated form, which causes the abnormal RBCs to sickle, as detected by light microscopy.
Sickle Cell Screen
Synonym/acronym: Sickle cell test.
To assess for hemoglobin S to assist in diagnosing sickle cell anemia.
SpecimenWhole blood (1 mL) collected in a lavender-top (EDTA) tube.
(Method: Hemoglobin high-salt solubility) Negative.
The sickle cell screen is one of several screening tests for a group of hereditary hemoglobinopathies. The test is positive in the presence of rare sickling hemoglobin (Hgb) variants such as Hgb S and Hgb C Harlem. Electrophoresis and high-performance liquid chromatography as well as molecular genetics testing for beta-globin mutations can also be used to identify Hgb S. Hgb S results from an amino acid substitution during Hgb synthesis whereby valine replaces glutamic acid. Hemoglobin C Harlem results from the substitution of lysine for glutamic acid. Individuals with sickle cell disease have chronic anemia because the abnormal Hgb is unable to carry oxygen. The red blood cells of affected individuals are also abnormal in shape, resembling a crescent or sickle rather than the normal disk shape. This abnormality, combined with cell-wall rigidity, prevents the cells from passing through smaller blood vessels. Blockages in blood vessels result in hypoxia, damage, and pain. Individuals with the sickle cell trait do not have the clinical manifestations of the disease but may pass the disease on to children if the other parent has the trait (or the disease) as well.
This procedure is contraindicated for
- Detect sickled red blood cells
- Evaluate hemolytic anemias
Positive findings in:
- Deoxygenated Hgb S is insoluble in the presence of a high-salt solution and will form a cloudy turbid suspension when present.
- Combination of Hgb S with other hemoglobinopathies
- Hgb C Harlem anemia
- Sickle cell anemia
- Sickle cell trait
- Drugs that may increase sickle cells in vitro include prostaglandins.
- A positive test does not distinguish between the sickle trait and sickle cell anemia; to make this determination, follow-up testing by Hgb electrophoresis should be performed.
- False-negative results may occur in children younger than 3 mo of age.
- False-negative results may occur in patients who have received a recent blood transfusion before specimen collection, as a result of the dilutional effect.
- False-positive results may occur in patients without the trait or disease who have received a blood transfusion from a sickle cell–positive donor; this effect can last for 4 mo after the transfusion.
- Test results are unreliable if the patient has pernicious anemia or polycythemia.
Nursing Implications and Procedure
- Positively identify the patient using at least two unique identifiers before providing care, treatment, or services.
- Patient Teaching: Inform the patient this test can assist in diagnosing anemia.
- Obtain a history of the patient’s complaints, including a list of known allergens, especially allergies or sensitivities to latex.
- Obtain a history of the patient’s hematopoietic system, symptoms, and results of previously performed laboratory tests and diagnostic and surgical procedures.
- Note any recent procedures that can interfere with test results.
- Obtain a list of the patient’s current medications, including herbs, nutritional supplements, and nutraceuticals (see Effects of Natural Products on Laboratory Values online at DavisPlus).
- Review the procedure with the patient. Inform the patient that specimen collection takes approximately 5 to 10 min. Address concerns about pain and explain that there may be some discomfort during the venipuncture.
- Sensitivity to social and cultural issues, as well as concern for modesty, is important in providing psychological support before, during, and after the procedure.
- Note that there are no food, fluid, or medication restrictions unless by medical direction.
- Potential complications: N/A
- Avoid the use of equipment containing latex if the patient has a history of allergic reaction to latex.
- Instruct the patient to cooperate fully and to follow directions. Direct the patient to breathe normally and to avoid unnecessary movement.
- Observe standard precautions, and follow the general guidelines in Patient Preparation and Specimen Collection. Positively identify the patient, and label the appropriate specimen container with the corresponding patient demographics, initials of the person collecting the specimen, date, and time of collection. Perform a venipuncture.
- Remove the needle and apply direct pressure with dry gauze to stop bleeding. Observe/assess venipuncture site for bleeding or hematoma formation and secure gauze with adhesive bandage.
- Promptly transport the specimen to the laboratory for processing and analysis.
- Inform the patient that a report of the results will be made available to the requesting health-care provider (HCP), who will discuss the results with the patient.
- Advise the patient with sickle cell disease to avoid situations in which hypoxia may occur, such as strenuous exercise, staying at high altitudes, or traveling in an unpressurized aircraft. Obstetric and surgical patients with sickle cell anemia are at risk for hypoxia and therefore require close observation: Obstetric patients are at risk for hypoxia during the stress of labor and delivery, and surgical patients may become hypoxic while under general anesthesia.
- Recognize anxiety related to test results, and offer support, as appropriate. Discuss the implications of abnormal test results on the patient’s lifestyle. Provide teaching and information regarding the clinical implications of the test results, as appropriate. Educate the patient regarding access to counseling services (www.sicklecelldisease.org).
- Reinforce information given by the patient’s HCP regarding further testing, treatment, or referral to another HCP. Inform the patient that further testing may be indicated if results are positive. Answer any questions or address any concerns voiced by the patient or family.
- Depending on the results of this procedure, additional testing may be performed to evaluate or monitor progression of the disease process and determine the need for a change in therapy. Evaluate test results in relation to the patient’s symptoms and other tests performed.
- Related tests include biopsy bone marrow, CBC, CBC RBC morphology, CBC RBC indices, ESR, Hgb electrophoresis, hemosiderin, LAP, MRI musculoskeletal, newborn screening, RBC cholinesterase, and US spleen.
- Refer to the Hematopoietic System table at the end of the book for related tests by body system.