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الرئيسية » 🔬موسوعة التحاليل الطبية » Biochemistry » Hemoglobin Electrophoresis (Hgb Electrophoresis)

Hemoglobin Electrophoresis (Hgb Electrophoresis)

Hemoglobin Electrophoresis (Hgb Electrophoresis)


NORMAL FINDINGS
Adult/elderly: percentage of total hemoglobin
Hgb A1: 95%-98%
Hgb A2: 2%-3%
Hgb F: 0.8%-2%
Hgb S: 0%
Hgb C: 0%
Hgb E: 0%
Children (Hgb F)
Newborn (Hgb F): 50%-80%
<6 months: <8%

>6 months: 1%-2%


INDICATIONS
Hgb electrophoresis is a test that enables abnormal forms of Hgb (hemoglobinopathies) to be detected and quantified. This test is used to diagnose sickle cell anemia, thalassemia, and other hemoglobinopathies.

TEST EXPLANATION

Although many different Hgb variations have been described, the more common types are A1, A2, F, S, E, and C. Each major Hgb type is electrically charged to varying degrees. When the Hgb from lysed red blood cells (RBCs) is placed on electrophoresis paper in an electromagnetic field, the Hgb variants mi￾grate at different rates and therefore spread apart from each other. The migration of the various forms of Hgb makes up a series of bands on the paper. The bands therefore correspond to the various forms of Hgb present. The pattern of bands is compared to normal and to well-known abnormal patterns. A diagnosis can then be made. Each band can be quantitated as a percentage of the total Hgb, indicating the severity of any recognized abnormality.
The form Hgb A1 constitutes the major component of Hgb in the normal RBC. Hgb A2 is only a minor component (2% to 3%) of the normal Hgb total. Hgb F is the major Hgb component in the fetus but usu￾ally exists in only minimal quantities in the normal adult. Levels of Hgb F greater than 2% in patients over 3 years of age are considered abnormal. Hgb F is able to transport oxygen when only small amounts of oxygen are available (as in fetal life). In patients requiring compensation for prolonged chronic hy￾poxia (as in congenital cardiac abnormalities), Hgb F may be found in increased levels to assist in the transport of the available oxygen.
Hgb S and Hgb C are abnormal forms of Hgb that occur predominantly in American blacks. Hemoglobin E occurs predominantly in Southeast Asians. Hgb S is associated with sickle cell anemia. Hgb S is a relatively insoluble variant. When little oxygen is available, it assumes a crescent (sickle) shape that greatly distorts the RBC morphology. Vascular sludging is a consequence of the localized sickling and may lead to organ infarction. The duration of survival of the sickled RBC is diminished, and these patients also have anemia. RBCs containing Hgb C have a decreased life span and are more readily lysed than normal RBCs. Mild to severe hemolytic anemia may result. The Hgb contents of some common disorders affecting hemoglobin, as determined by electrophoresis, are indicated in Table 2-27.
Hgb E is produced less efficiently by RBC precursors; if there is an increased Hgb E content in the RBCs, those cells will have a low mean corpuscular volume (MCV, ).
Quantifying abnormal hemoglobins is helpful in determining the zygosity of a familial hemoglobinopathy. Furthermore quantification of abnormal hemoglobin proteins provides a method of monitoring treatments designed to increase more effective hemoglobin variants and decrease abnormal variants.
Hemoglobin quantification can be performed by high-performance liquid chromatography (HPLC) and polymerase chain reaction (PCR) analysis.

INTERFERING FACTORS

• Blood transfusions within the previous 12 weeks may alter test results.
• Glycosylated Hgb can blur the peak of Hgb F and cause falsely low levels of Hgb F.
PROCEDURE AND PATIENT CAREBefore
➢ Explain the procedure to the patient.
➢ Tell the patient that no fasting is required.
During
• Collect a venous blood sample in a lavender-top tube.
After
• Apply pressure or a pressure dressing to the venipuncture site.
• Assess the venipuncture site for bleeding.
TEST RESULTS AND CLINICAL SIGNIFICANCE
⇧⇧⇧  Increased Levels
Sickle cell disease,
Hemoglobin H disease,
Thalassemia major,
Sickle cell trait,
Thalassemia minor,
Hemoglobin C trait or disease,
Hemoglobin E trait or disease:
These hemoglobinopathies have a “classic” Hgb electrophoresis pattern that is diagnostic for the respective
disease.

حول: هلال سود
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