Alpha and beta thalassaemia

01OverviewDefinition, clinical context and the essential points that orientate the chapter.

Adult haemoglobin contains two alpha and two beta chains. Alpha genes are duplicated on each chromosome 16, so the number and arrangement of affected genes determine alpha-thalassaemia. Beta-globin is encoded on each chromosome 11, and beta-zero or beta-plus variants abolish or reduce output. Unpaired chains precipitate within erythroid cells: excess alpha chains are particularly damaging in beta-thalassaemia, causing profound ineffective erythropoiesis, while beta-chain tetramers form HbH when alpha output is markedly reduced.

Investigation begins with a valid full count, film and iron status. Target cells and microcytosis support thalassaemia but are not specific. Haemoglobin analysis measures HbA2, HbF and variants; a raised HbA2 commonly supports beta trait. Alpha trait can leave adult fractions normal. Recent transfusion mixes donor haemoglobin, and iron deficiency may lower HbA2, so timing and context matter. Molecular analysis confirms uncertain or clinically important genotypes and is essential for some alpha reproductive-risk questions.

Management distinguishes carrier reassurance from disease care. Carriers need no transfusion or iron unless independently deficient. HbH and intermedia phenotypes need specialist follow-up for haemolysis, growth, gallstones, bone health, thrombosis, endocrine complications and iron loading that can arise from absorption even without regular transfusion. Transfusion-dependent beta-thalassaemia requires a separate lifelong programme. Genetic counselling should be non-directive, document each partner's genotype and offer timely fetal diagnostic or preimplantation routes through the NHS pathway.

Key points

Thalassaemias are inherited reductions in alpha- or beta-globin synthesis, causing microcytosis, globin-chain imbalance and ineffective erythropoiesis of variable severity.
Trait commonly produces a low MCV and MCH out of proportion to mild or absent anaemia, with a relatively preserved red-cell count.
Check ferritin before attributing microcytosis to carrier status; iron deficiency and thalassaemia can coexist and only documented deficiency should receive iron.
Beta-thalassaemia trait usually raises haemoglobin A2 after infancy, while iron deficiency, recent transfusion and some variants can complicate quantification.
Alpha-thalassaemia trait often has normal adult high-performance liquid chromatography or electrophoresis, so molecular testing may be required when reproductive risk matters.
Loss of one alpha gene is usually silent, two causes trait, three produces HbH disease, and loss of all four causes alpha-thalassaemia major with fetal hydrops.
Beta-thalassaemia phenotypes range from asymptomatic carrier to non-transfusion-dependent and transfusion-dependent disease according to the paired variants and modifiers.
HbH disease can produce chronic haemolysis, splenomegaly, gallstones and oxidative crises with infection or medicines, especially in non-deletional forms.
Carrier identification is clinically important for reproductive counselling, but should not be presented as illness, racialised assumption or a reason to deny normal activity.
At-risk couples require counselling that integrates both partners' results, cis or trans alpha-gene arrangement, variant severity and available prenatal or preimplantation options.

02AetiologyUnderlying causes, associations and risk factors, with why each one matters.

Alpha-gene deletion or variant

Deletions remove one or more HBA genes, while non-deletional variants reduce function. The chromosome arrangement determines the chance of a pregnancy inheriting no working alpha genes.

Beta-globin variants

HBB variants reduce or abolish beta-chain output; the two inherited alleles and modifiers of fetal haemoglobin determine carrier, intermedia or major clinical severity.

Autosomal inheritance

Disease follows inheritance from both biological parents, while carrier states affect reproductive probability rather than inevitably causing clinical illness in the carrier.

03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.

1
Chain imbalance
Reduced production of one globin type leaves unmatched partner chains that precipitate, damage erythroblast membranes and impair maturation or circulating red-cell survival.
2
Ineffective erythropoiesis
Intramedullary death expands erythropoietin-driven marrow and suppresses hepcidin, producing anaemia, skeletal change and increased iron absorption in more severe phenotypes.
3
HbH instability
With only one effective alpha gene, excess beta chains form HbH tetramers that carry oxygen abnormally and precipitate under oxidative stress, promoting haemolysis.
4
Fetal oxygen failure
Absence of all four alpha genes produces gamma-chain tetramers with very high oxygen affinity, causing profound fetal tissue hypoxia, anaemia and hydrops.

04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.

Trait indices

Persistent low MCV and MCH with mild anaemia and a relatively high red-cell count suggests a carrier state after iron assessment.

Beta-trait fraction

Raised HbA2 supports beta-thalassaemia trait when age, iron status, transfusion and coexisting variants are considered.

Alpha-trait invisibility

Normal adult haemoglobin fractions do not exclude alpha-thalassaemia trait, particularly when indices and reproductive ancestry are compatible.

HbH disease

Chronic microcytic haemolysis, splenomegaly and HbH on analysis indicate three-gene alpha impairment and risk of episodic deterioration.

Hydrops riskRed flag

Both partners carrying alpha-zero deletions in cis creates a pregnancy at risk of alpha-thalassaemia major requiring urgent fetal referral.

05InvestigationsWhat to request, why it matters and how to interpret it.

Investigation order

Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.

01
Full blood count and filmFirst step
Why
Define microcytosis, red-cell number and haemolytic morphology.
Interpretation and limitations
Target cells and disproportionate microcytosis support thalassaemia but do not distinguish alpha, beta or iron deficiency without further tests.
02
Ferritin and inflammatory context
Why
Identify coexisting iron deficiency before haemoglobin interpretation.
Interpretation and limitations
Low ferritin supports depletion; a normal or raised value during inflammation may need transferrin saturation or repeat assessment.
03
HPLC or capillary electrophoresis
Why
Quantify HbA2, HbF and structural variants.
Interpretation and limitations
Raised HbA2 often supports beta trait; normal fractions do not exclude alpha trait, and transfusion creates mixed donor peaks.
04
Alpha- and beta-globin molecular analysis
Why
Define clinically significant or reproductively relevant variants.
Interpretation and limitations
Testing clarifies silent alpha deletions, cis or trans arrangement, non-deletional disease and uncertain beta alleles and needs genetics interpretation.
05
Partner testing
Why
Calculate the genotype-specific risk to a pregnancy.
Interpretation and limitations
Both partners' count, haemoglobin analysis and targeted molecular results are considered together; ethnicity alone cannot provide an individual probability.
06
Haemolysis and iron-organ assessment
Why
Stage HbH or intermedia complications.
Interpretation and limitations
Reticulocytes, bilirubin, liver iron MRI and endocrine or cardiac tests are selected by phenotype, transfusions and ferritin trajectory.

06Differential diagnosisRealistic alternatives and the features that help distinguish them.

Iron deficiency

Iron depletion causes microcytosis with low ferritin and often a lower red-cell count; coexistence is common enough that neither condition should be inferred from indices alone.

Anaemia of inflammation

Inflammatory iron restriction may lower MCV and serum iron while ferritin rises, but haemoglobin fractions and family studies do not show a thalassaemic inheritance pattern.

Sideroblastic anaemia

Defective haem synthesis causes iron-loaded ineffective erythropoiesis and marrow ring sideroblasts; exposure, clonal studies and iron results separate it from globin underproduction.

Structural haemoglobin variant

HbS, HbC, HbE and other variants alter haemoglobin analysis and may coexist with thalassaemia, requiring laboratory and genomic interpretation rather than a trait label alone.

07ManagementImmediate care, first-line treatment, alternatives and escalation.

01MicrocytosisSeparate globin from iron physiologyFirst stepA low MCV or MCH persists with mild or no anaemia.

1Obtain ferritin with inflammatory context and review diet, bleeding, pregnancy, transfusion, ancestry and family blood-count history.
2Perform accredited haemoglobin analysis before iron treatment when deficiency is not established, recognising the limitations for alpha trait.
3Refer for molecular testing when results are discordant, HbH is possible or a partner combination could create a severe fetal genotype.

02Clinical diseaseStage haemolysis and iron burdenHbH, non-transfusion-dependent beta-thalassaemia or another symptomatic genotype is confirmed.

1Establish baseline haemoglobin, reticulocytes, haemolysis, spleen and gallstone symptoms, transfusion history, growth, bone and endocrine health.
2Use episodic or regular transfusion only for defined symptomatic or physiological indications and select matched products with antibody surveillance.
3Assess absorbed and transfused iron using trends and specialist MRI, initiating chelation when validated thresholds and anticipated benefit support it.

03Reproductive careResolve both parental genotypesA carrier is pregnant, planning pregnancy or has a partner with possible haemoglobinopathy.

1Test the partner promptly using full count and haemoglobin analysis, adding molecular studies needed to define alpha arrangement or interacting variants.
2Provide non-directive genetics counselling with the specific inheritance probability, phenotype range and limitations rather than a generic high-risk label.
3Offer timely prenatal diagnosis, preimplantation testing or other reproductive options through fetal medicine and clinical genetics according to informed preference.

Key medicines and prescribing safety3 treatments · regimens, roles and cautions

Supports increased marrow turnover in clinically haemolytic disease but is not required routinely for every asymptomatic carrier.

Folic acid in significant haemolysis

Specialists commonly prescribe 5 mg orally once daily during pregnancy or sustained HbH or intermedia haemolysis when erythropoietic demand makes folate depletion plausible.

Assess vitamin B12 where appropriate and do not let folate obscure the need to investigate a new anaemia or provide genotype-specific care.

Treats coexisting iron deficiency; it does not correct globin-chain underproduction or normalise carrier microcytosis.

Iron replacement for proven deficiency

Use the NICE or BNF oral elemental-iron regimen and duration only after deficiency is demonstrated, adjusting frequency for tolerance and expected absorption.

Avoid indefinite empirical iron because intermedia syndromes may already absorb excess iron; confirm response and investigate the source of deficiency.

Corrects clinically important anaemia in HbH, intermedia or severe beta-thalassaemia while definitive or long-term plans are made.

Red-cell transfusion

Haemoglobinopathy specialists prescribe antigen-matched component volume and interval from symptoms, growth, pregnancy, acute haemolysis and safe post-transfusion haemoglobin rather than trait status.

Alloimmunisation, reactions, hyperviscosity, volume overload and iron accumulation require consent, antibody history and longitudinal monitoring.

08ComplicationsImportant consequences, why they occur and why they matter clinically.

Iron overload

Increased absorption from ineffective erythropoiesis and transfused iron can damage liver, endocrine glands and heart even in some non-transfusion-dependent phenotypes.

Haemolytic crisis

HbH disease may worsen abruptly during infection or oxidative stress, causing jaundice, reticulocytosis and symptomatic anaemia that occasionally needs transfusion.

Gallstones and splenomegaly

Chronic haemolysis increases bilirubin stone formation and splenic clearance, leading to pain, cytopenias and occasional carefully selected surgical discussion.

Affected pregnancy

When both parents carry compatible variants, offspring may inherit transfusion-dependent beta-thalassaemia or alpha-thalassaemia major, making timely counselling and fetal testing important.

09Monitoring and follow-upTreatment response, safety checks and longer-term review.

Asymptomatic carriers need result documentation and reproductive access, not repeated haematology visits solely to normalise the MCV.
For HbH or intermedia follow haemoglobin, reticulocytes, bilirubin, spleen, gallstone symptoms and transfusion requirement at phenotype-based intervals.
Track ferritin trends and obtain validated liver or cardiac iron imaging when absorption, transfusion history or organ features make loading plausible.
Monitor growth, puberty, bone density, glucose, thyroid, gonadal and cardiac health in more severe ineffective-erythropoiesis phenotypes.
During pregnancy share genotype, antibody and transfusion plans across haematology, fetal medicine, anaesthesia and the blood bank.
Update family and partner testing after molecular reclassification or a new pregnancy because reproductive risk depends on the exact variant pairing.

10Special situationsVariants, exceptions and circumstances that change the usual approach.

Alpha trait may hide

Adult haemoglobin separation can be normal, so compatible microcytosis and reproductive risk sometimes require DNA-based confirmation.

Two-gene arrangement matters

Alpha deletions in cis create different fetal risk from the same number split across homologous chromosomes.

Microcytosis needs no cure

A well carrier does not benefit from forcing the MCV into range with iron when stores are adequate.

Non-transfused can load iron

Ineffective erythropoiesis suppresses hepcidin and increases absorption, so iron overload is not confined to chronic transfusion programmes.

11Common pitfallsFrequent interpretation and management errors.

01
Diagnosing iron deficiency from MCV alone.
02
Excluding alpha trait after normal electrophoresis.
03
Failing to establish the partner's genotype promptly.
04
Calling carrier status a symptomatic disease automatically.
05
Ignoring iron loading in non-transfusion-dependent disease.
06
Interpreting post-transfusion haemoglobin fractions as native.