Sickle Cell Tests

Tests

Testing for sickle cell is performed to identify the presence of hemoglobin S, the presence of other abnormal hemoglobin variants, to evaluate the status and number of the patient’s RBCs, and/or to determine whether a patient has one or more altered hemoglobin gene copies.

Sickle cell tests are ordered when someone wants to know if they have sickle cell disease or are carrying the sickle cell trait. The test performed depends on the specific purpose, be it screening or confirmation of disease. Newborn screening for sickle cell is performed routinely in most U.S. states and territories. This testing can identify the specific types of hemoglobin present. This and other testing that may be performed include:

For Screening:

Hb S solubility test. A chemical is added to the patient’s blood sample that reduces the amount of oxygen it carries. In those who carry even one sickle cell gene, some hemoglobin S will be present. The reduced amount of oxygen will cause S-related polymers to form and the affected RBCs to sickle. This test detects the presence of hemoglobin S. It should not be performed on infants until they are about 6 months old because babies with sickle cell will not produce significant amounts of hemoglobin S until several months after birth.

For Screening, Diagnosis and Confirmation:

DNA analysis. This test is used to investigate alterations and mutations in the genes that produce hemoglobin components. It can determine whether a patient has one copy of the hemoglobin S gene, two copies, or copies of different hemoglobin variants. It may be ordered for:

Prenatal testing: amniotic fluid may be tested at 14–16 weeks to provide a definitive answer. Genetic counseling is strongly encouraged if a positive sickle screen from one or both parents is determined. It can also be performed earlier with chorionic villi sampling.

Can be performed on individuals to confirm a diagnosis and to confirm sickle cell trait status. Family studies can be done to identify sickle cell trait in other family members.

Hemoglobinopathy (Hb) evaluation. There are several methods of evaluating the type and relative amount of hemoglobin present: Hb determination can be performed by electorphoresis using cellulose acetate or acid citrate agar, by isoelectric focusing or by Hb fractionation by HPLC. In hemoglobin electrophoresis, a patient’s blood sample is subjected to an electromagnetic field; different types of hemoglobin will migrate in patterns forming unique bands that enable a definitive diagnosis. In newborns with sickle cell, fetal hemoglobin F will predominate, but some hemoglobin S will also be present.

All newborn screening is performed via the more sensitive Hb isoelectric focusing or HPLC fractionation. As the infant grows, The amount of Hb S will increase as F decreases. At about age 2, the amount of Hb S and Hb F stabilizes. Adult patients with sickle cell trait will continue to produce a a majority of normal hemoglobin A, while patients with sickle cell anemia will have little or no Hb A Patients who are heterozygous for two different hemoglobin variants will usually produce varying amounts of both types.

Other tests that may be ordered to help evaluate the number and status of the patient’s RBCs include:

CBC (complete blood count). The CBC is a snapshot of the cells and fluid in your bloodstream. Among other things, the CBC will tell the doctor how many red blood cells are present, how much hemoglobin is in them, and give the doctor an evaluation of the size and shape of the red blood cells present. This test can be used to detect anemia.

Blood smear (also called peripheral smear and manual differential). In this test, a trained laboratorian looks at a thin stained layer of blood on a slide under a microscope. The number and type of white blood cells, red blood cells, and platelets can be evaluated to see if they are normal and mature. Sickled cells and cell fragments can be seen on the blood smear.

Iron studies. These may include: Iron, Ferritin, UIBC, TIBC, and Percent Saturation of Transferrin. These tests measure different aspects of the body’s iron storage and usage. They are ordered to help determine whether an iron deficiency is causing and/or exacerbating a patient’s anemia and can be used to detect and evaluate excess iron. Patients with sickle cell anemia who receive multiple blood transfusions may experience an iron overload.