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Introduction ⬇

Sickle cell disease is a term for a group of hereditary blood disorders. Sickle cell anemia is caused by an abnormality of Hb, the red protein in RBCs that carries oxygen from the lungs to the tissues. People with sickle cell disease make an abnormal Hb, hemoglobin S (Hb S). The RBCs of a person with sickle cell disease do not last as long as normal RBCs. This result is chronic anemia. Also, these RBCs lose their normal disk shape. They become rigid and deformed and take on a sickle or crescent shape. These oddly shaped cells are not flexible enough to squeeze through small blood vessels. This may result in blood vessels being blocked. The areas of the body served by those blood vessels will then be deprived of their blood circulation, damaging tissues and organs. This homozygous state of Hb S disease is associated with considerable morbidity and mortality. The heterozygous state presents little mortality.

This blood measurement is routinely done as a screening test for sickle cell anemia or trait and to confirm these disorders. This test detects Hb S, an inherited, recessive gene. An examination is made of erythrocytes for the sickle-shaped forms characteristic of sickle cell anemia or trait. This is done by removing oxygen from the erythrocyte. In erythrocytes with normal Hb, the shape is retained, but erythrocytes containing Hb S assume a sickle shape. However, the distinction between sickle cell trait and sickle cell disease is done by electrophoresis, which identifies an Hb pattern. Screening in adult women and their partners is recommended during pre- and postnatal care and for newborns as early as 24–48 hours following birth.

Normal Findings ⬆ ⬇

Adult: none present (i.e., negative)

Procedure ⬆ ⬇

  1. Obtain a venous blood sample of 5 mL in a lavender-topped tube with EDTA. Invert immediately 8–10 times to mix with the anticoagulant. Label the specimen with the patient’s name, date and time of collection, and test(s) ordered. Place the specimen in a biohazard bag.

  2. Perform the Sickledex test or Hb electrophoresis. Electrophoresis is more accurate and should be done in all positive Sickledex screens.

Clinical Implications ⬆ ⬇

A positive test (Hb S present) means that great numbers of erythrocytes have assumed the typical sickle cell (crescent) shape. Positive tests are 99% accurate.

  1. Sickle cell trait

    1. Definite confirmation of sickle cell trait by Hb electrophoresis reveals the following heterozygous (A/S) pattern: Hb S, 20%–40%; HbA1, 60%–80%; and Hb F, small amount. This means that the patient has inherited a normal Hb gene from one parent and an Hb S gene from the other (heterozygous pattern). This patient does not have any clinical manifestations of the disease, but some of the children of this patient may inherit the disease if the patient’s mate also has the recessive gene pattern.

    2. The diagnosis of sickle cell trait does not affect longevity and is not accompanied by signs and symptoms of sickle cell anemia. A/S occurs in 8.5% of Black people in the United States.

    3. Sickle cell trait can lead to renal papillary necrosis, hematuria, increased risk for pulmonary embolus, and anterior segment ischemia.

  2. Sickle cell anemia (Hb S disease)

    1. Definite confirmation of sickle cell anemia by Hb electrophoresis reveals the following homozygous (S/S) pattern: Hb S, 80%–100%; Hb F, most of the rest; HbA1, 0% (absent).

    2. This means that an abnormal Hb S gene has been inherited from both parents (homozygous pattern). Such a patient has all the clinical manifestations of the disease.

  3. Hb C—Harlem (rare)

  4. Hb C—Georgetown

  5. Hb S in combination with other disorders, such as beta-thalassemia or Hb SC

Interventions ⬆ ⬇

Pretest Patient Care

  1. Explain test purpose and procedure. Assess for signs/symptoms of aching bones, cardiomegaly, chest pain, fatigue, murmurs, dyspnea, pallor, joint swelling, and jaundice.

  2. Provide genetic counseling.

  3. Follow guidelines in Chapter 1 for safe, effective, informed pretest care.

Posttest Patient Care

  1. Review test results; report and record findings. Modify the nursing care plan as needed. Counsel the patient regarding abnormal findings; explain the need for possible follow-up testing and treatment.

  2. A positive diagnosis of sickle cell disorder has genetic implications, including the need for genetic counseling.

  3. A person with sickle cell disease should avoid situations in which hypoxia may occur, such as very strenuous exercise, traveling to high-altitude regions, or traveling in an unpressurized aircraft.

  4. Because of the hypoxia created by general anesthetic agents and a state of shock, surgical and maternity patients with sickle cell disease need very close observation.

  5. Possible treatments include administering vaccines (Haemophilus influenzae B) and analgesic drugs as ordered.

  6. Oral hydroxyurea, an antineoplastic drug, inhibits Hb S production and increases Hb F synthesis.

  7. Follow guidelines in Chapter 1 for safe, effective, informed posttest care.

Interfering Factors ⬆

  1. False-negative results occur in:

    1. Infants younger than 3 months of age (maximal amounts reached by 6 months)

    2. Coexisting thalassemias or iron deficiency

  2. False-positive results occur up to 4 months after transfusion with RBCs having sickle cell trait.

  3. Hb D and Hb G migrate to the same place as Hb F in electrophoresis.

  4. The solubility test is unreliable in pernicious anemia and polycythemia.

Clinical Alert

A positive Sickledex test must be confirmed by electrophoresis.Assess for sickle cell crisis: pale lips, tongue, palms, or nail beds; lethargy; listlessness; pain; and increased temperature