Required section · Section 3 of 6
Focused instruction
For a person older than 12 months, cited beta-thalassemia carrier pattern data include HbA2 above 4%, HbF below 5%, and HbA above 88% (Beta-Thalassemia GeneReviews). A practical screening convention uses HbA2 greater than 3.5% (NCBI hemoglobin-disorder screening reference). Neither is a universal interval or a genotype call. Your laboratory must validate its interval and decision process on its own method.
Iron deficiency matters because severe deficiency can lower HbA2 into the normal range in a beta-thalassemia carrier. A normal or borderline HbA2 therefore does not resolve a discordant microcytic pattern. Delta-thalassemia and delta-beta-thalassemia can also alter HbA2 or HbF. Do not use one fraction to infer a beta genotype.
On this cation-exchange HPLC workflow, an HbE or Hb Lepore fraction can co-elute in the HbA2 retention window: do not report the combined peak as HbA2; inspect the chromatogram under the validated window rule and resolve it with an alternate separation method or approved reflex. In an HbS-containing specimen, HbS adducts can overlap the HbA2 window and spuriously affect integration: apply the local HbS/HbA2 integration rule and use a complementary method if the assignment remains uncertain. An alpha-chain variant can create a separate or poorly resolved abnormal peak that compromises the baseline used to integrate nearby fractions: review peak shape and baseline under the local integration rule, then use an alternate method when resolution is inadequate.
Recent red-cell transfusion can make fractionation a mixture of patient and donor cells. Newborns are different because HbF predominates at birth, and adult percentage patterns do not apply. Hb Bart greater than 15% on newborn dried-blood-spot HPLC or isoelectric focusing is suggestive of HbH disease (Alpha-Thalassemia GeneReviews), while local newborn cutoffs vary. Document age, iron studies, transfusion date, and the local validated method before interpreting HbA2 or HbF.
HbA2 is a calculated fraction: in this chromatogram assignment, the HbA2 window integrates 46,000 area units from 1,000,000 total reportable area units, so HbA2 = (46,000 ÷ 1,000,000) × 100 = 4.6%. Do not transfer this calculation to a co-eluting, overlapping, or poorly resolved window; follow the local method's assignment, review, and alternate-method pathway.
Illustrative drawing — this picture was drawn rather than captured.
| Pattern | CBC or smear | Fraction clue | Interpretation limit |
|---|---|---|---|
| Beta carrier pattern | Microcytosis, relatively increased RBC count, target cells | HbA2 often increased | Iron status and method can alter HbA2 |
| Alpha trait pattern | Microcytosis may be present | Adult analysis may be nondiagnostic | Molecular testing may be needed |
| HbH pattern | Variable anemia and microcytosis | HbH may be detectable after birth | Confirm HBA1 and HBA2 variants molecularly |
| Severe beta pattern | More anemia, anisopoikilocytosis, nucleated RBCs by severity | HbF may be increased | Age and transfusion history alter interpretation |
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