Hemoglobin Electrophoresis & Sickle Cell Testing: Interpreting the Patterns

 

Hemoglobin Electrophoresis & Sickle Cell Testing: Interpreting the Patterns

Trait vs. disease, thalassemia clues on the CBC, and why the newborn screen needs follow-up.

Hemoglobin electrophoresis separates hemoglobin variants by their electrical charge, identifying the type and proportion of each hemoglobin present. It's the definitive test for diagnosing hemoglobinopathies—but it's also one of the most misunderstood results in primary care.

Normal Hemoglobin Composition

  • HbA (adult hemoglobin): 95–98% (two alpha + two beta globin chains)
  • HbA2: 2–3.5% (two alpha + two delta chains)
  • HbF (fetal hemoglobin): <1% in adults (two alpha + two gamma chains; predominates in utero and declines after birth)

The Key Patterns

ConditionHbAHbSHbA2HbFCBC Clues
Normal95–98%02–3.5%<1%Normal
Sickle cell trait (AS)55–60%35–45%NormalNormalUsually normal CBC. No anemia. Benign in most contexts.
Sickle cell disease (SS)080–95%Normal2–20%Chronic hemolytic anemia, reticulocytosis, sickle cells on smear
HbSC disease0~45% S, ~45% CNormalLowMilder anemia than SS; target cells on smear; still has vaso-occlusive crises
Beta-thalassemia trait90–95%0>3.5%Normal/slightly ↑Microcytic anemia with normal RDW and elevated RBC count. Mentzer index (MCV/RBC) <13 favors thalassemia.
Beta-thalassemia major0–10%0Variable60–90%Severe transfusion-dependent anemia from infancy
Alpha-thalassemia trait (2-gene deletion)Normal pattern0NormalNormalMicrocytic anemia with normal electrophoresis. Diagnosis by exclusion or genetic testing.
HbH disease (3-gene alpha deletion)Reduced0ReducedNormalHbH (beta-4 tetramers) visible on special stain or HPLC. Moderate hemolytic anemia.
The Alpha-Thalassemia Trap

Alpha-thalassemia trait (1–2 gene deletions) has a completely normal hemoglobin electrophoresis. The only clues are microcytosis with normal iron studies and normal HbA2. If you've ruled out iron deficiency and the electrophoresis is normal, alpha-thalassemia trait is the diagnosis by exclusion (confirm with genetic testing if needed). This is extremely common in African American, Southeast Asian, and Mediterranean populations.

Thalassemia Trait vs. Iron Deficiency: The CBC Distinction

Both cause microcytic anemia. The CBC pattern distinguishes them:

  • Iron deficiency: Low MCV, high RDW (unequal cells), low/normal RBC count, low ferritin, high TIBC
  • Thalassemia trait: Low MCV, normal RDW (uniformly small cells), elevated RBC count, normal iron studies, elevated HbA2 (beta-thal) or normal electrophoresis (alpha-thal)

Newborn Screening Follow-Up

Pediatric Critical Point

All US states screen for hemoglobinopathies on the newborn metabolic panel. Results are reported as the hemoglobins detected in order of quantity: FA = normal (Fetal predominant, Adult present). FAS = sickle cell trait. FS = possible sickle cell disease (no HbA detected—needs urgent confirmatory testing). FSC = HbSC disease. Any abnormal newborn screen requires confirmatory hemoglobin electrophoresis by 2–3 months of age and genetic counseling. Early identification of sickle cell disease enables penicillin prophylaxis starting at 2 months, which dramatically reduces mortality from pneumococcal sepsis.

Connections to This Series

  • HbA1c post: Hemoglobinopathies make A1c unreliable. HbS, HbC, HbE interfere with assays.
  • CBC post: MCV + RDW + RBC count pattern distinguishes thalassemia from iron deficiency.
  • Iron studies post: Always check iron studies before diagnosing thalassemia. Coexisting iron deficiency can mask thalassemia, and iron overload from transfusions is a major complication.

Bottom Line

Hemoglobin electrophoresis diagnoses sickle cell disease, beta-thalassemia, and hemoglobin variants definitively. Alpha-thalassemia trait is the exception—it has a normal electrophoresis and is diagnosed by exclusion. Use the CBC pattern (MCV, RDW, RBC count) to guide when to order electrophoresis, and always follow up abnormal newborn screens promptly.

Stay sharp out there.

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