Sideroblastic anaemia

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

Haem synthesis partly occurs in erythroblast mitochondria. When synthesis, iron-sulphur handling or mitochondrial function fails, imported iron cannot be incorporated effectively and accumulates around the nucleus. The marrow may be erythroid rich because precursors expand but die before release, producing anaemia despite abundant stored iron. Peripheral cells can be microcytic in congenital ALAS2 deficiency, macrocytic in clonal disease or mixed after transfusion and variable clone expression.

The diagnostic task is to explain the ring-sideroblast phenotype. Begin with count, reticulocytes, film and iron studies, then reconstruct exposures and nutritional risk. Basophilic stippling supports but does not prove lead toxicity. Low copper and caeruloplasmin with excess zinc or malabsorption require careful interpretation. In an older adult with persistent unexplained cytopenia, marrow morphology, cytogenetics and a myeloid mutation panel assess a myelodysplastic neoplasm. In a younger person or lifelong microcytosis, genomic evaluation may identify congenital sideroblastic anaemia.

Management follows cause and burden. Stop alcohol or an offending drug with the relevant prescriber, replace copper deficiency while removing excess zinc, and use public-health or occupational pathways for lead. A supervised pyridoxine trial can produce a substantial response in ALAS2-related disease. Clonal disease treatment depends on risk, symptoms and transfusion dependence and may include erythropoiesis-stimulating treatment, luspatercept under current eligibility, disease-modifying therapy or transplantation. Red-cell support and iron chelation are specialist decisions tied to symptoms, transfusion burden and organ iron.

Key points

Sideroblastic anaemia describes ineffective erythropoiesis in which iron accumulates within mitochondria encircling erythroblast nuclei as ring sideroblasts on marrow iron staining.
It is a morphological mechanism rather than one disease: causes include inherited ALAS2-related disease, myelodysplastic neoplasms, alcohol, medicines, copper deficiency and lead toxicity.
The mean cell volume may be low, normal or high; a dimorphic film and raised ferritin or transferrin saturation can suggest iron-loaded ineffective erythropoiesis.
Ring sideroblasts require a bone-marrow aspirate stained for iron and must be distinguished from ordinary sideroblasts that lack the characteristic perinuclear mitochondrial distribution.
History should specifically cover alcohol, isoniazid, linezolid, chloramphenicol, zinc exposure, bariatric surgery, occupational lead and family or childhood anaemia.
Copper deficiency may follow gastrointestinal surgery, malabsorption or excess zinc and can produce anaemia, neutropenia and neurological disease that mimics myelodysplasia.
Pyridoxine responsiveness is characteristic of some ALAS2-related disease and selected drug-associated cases, but empiric indefinite high doses can cause sensory neuropathy.
Clonal sideroblastic anaemia requires integrated marrow morphology, blast count, cytogenetics and molecular testing such as SF3B1 rather than classification by ring percentage alone.
Remove a reversible toxin or medicine when clinically safe, replace documented deficiency and involve occupational services or toxicology where exposure persists.
Chronic ineffective erythropoiesis and transfusions can load iron even without routine oral supplementation, requiring ferritin trends and specialist organ iron assessment.

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

Inherited haem-pathway defects

Variants in ALAS2 and other mitochondrial or iron-sulphur genes impair haem production, sometimes causing childhood disease and sometimes an X-linked phenotype recognised only in adulthood.

Acquired reversible injury

Alcohol, lead, copper deficiency and medicines including isoniazid or prolonged linezolid can disrupt mitochondrial haem synthesis or cofactor availability.

Clonal myeloid disease

Myelodysplastic neoplasms with SF3B1 mutation or related clonal abnormalities produce ring sideroblasts alongside ineffective, dysplastic haematopoiesis and age-dependent risk of progression.

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

1
Failed haem incorporation
Iron enters erythroblast mitochondria but cannot be incorporated normally into protoporphyrin, leaving perinuclear iron-laden organelles visible with Prussian-blue staining.
2
Ineffective erythropoiesis
Abnormal erythroblasts undergo intramedullary death, so the marrow can be hypercellular while reticulocyte output and circulating haemoglobin remain inappropriately low.
3
Systemic iron accumulation
Suppressed hepcidin from ineffective erythropoiesis can increase absorption, and repeated transfusion adds non-excretable iron, eventually threatening liver, heart and endocrine organs.

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

Dimorphic indices

Mixed microcytic and normocytic or macrocytic populations can widen red-cell distribution and obscure the mechanistic pattern in a single MCV.

Iron-loaded anaemia

Low haemoglobin with raised ferritin and transferrin saturation despite no iron prescription suggests ineffective use rather than simple deficiency.

Exposure phenotype

Abdominal pain, neuropathy or cognitive symptoms with basophilic stippling and occupational risk raises lead toxicity requiring confirmation.

Rapid clonal changeRed flag

New severe cytopenias, circulating blasts, infection or bleeding needs urgent myeloid-neoplasm assessment rather than routine nutritional follow-up.

Copper clue

Anaemia plus neutropenia and sensory ataxia after bariatric surgery or high zinc exposure should prompt copper evaluation.

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 count, reticulocytes and filmFirst step
Why
Define cell size, dimorphism and other cytopenias.
Interpretation and limitations
Low reticulocyte output fits ineffective production; basophilic stippling, Pappenheimer bodies or dysplasia guide but do not establish cause.
02
Ferritin and transferrin saturation
Why
Assess iron availability and possible overload.
Interpretation and limitations
Raised values support iron abundance but inflammation and liver disease alter ferritin; do not give empirical iron without demonstrated deficiency.
03
Bone-marrow aspirate with iron stain
Why
Demonstrate pathological ring sideroblasts and morphology.
Interpretation and limitations
Perinuclear iron granules in mitochondria define ring forms; trephine, blast count and dysplasia determine the broader marrow diagnosis.
04
Cytogenetic and myeloid molecular panel
Why
Identify clonal disease and prognostic abnormalities.
Interpretation and limitations
SF3B1 supports a defined myelodysplastic subtype in the correct setting, but mutation findings require integrated classification.
05
Copper, caeruloplasmin and zinc
Why
Detect a reversible nutritional or competitive cause.
Interpretation and limitations
Low copper with excess zinc or malabsorption is actionable; inflammatory changes and supplementation timing can affect measured concentrations.
06
Blood lead concentration
Why
Confirm clinically relevant lead exposure.
Interpretation and limitations
Interpret with toxicology and occupational-health thresholds, symptoms and ongoing exposure; film stippling alone is not diagnostic.
07
Congenital anaemia gene testing
Why
Identify inherited sideroblastic disease in compatible cases.
Interpretation and limitations
Genomic results guide pyridoxine response expectations, family testing and reproductive counselling and need specialist variant interpretation.

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

Iron deficiency

Both conditions may be microcytic, but iron deficiency usually has depleted ferritin and transferrin saturation rather than abundant marrow iron and systemic loading.

Thalassaemia

Globin-chain imbalance causes microcytosis with characteristic haemoglobin or genomic findings; target cells and family ancestry differ, although both may develop iron excess.

Anaemia of inflammation

Inflammatory iron restriction produces low circulating iron with preserved or raised ferritin but does not ordinarily create pathological perinuclear ring sideroblasts.

Other myelodysplasia

Clonal cytopenia without ring sideroblast predominance can show macrocytosis and dysplasia; integrated marrow and molecular classification determines the correct neoplasm category.

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

01PhenotypeProve iron-loaded ineffective productionFirst stepPersistent anaemia has atypical indices, dimorphism or unexpectedly high iron stores.

1Review count trajectory, reticulocytes, film and iron measures and stop reflex iron prescribing until true deficiency is demonstrated.
2Take a detailed alcohol, medicine, zinc, surgery, occupation and family history, then test copper and lead where exposure makes them plausible.
3Arrange marrow aspirate, trephine, iron stain and clonal studies through haematology when anaemia persists or additional cytopenias suggest myelodysplasia.

02Reversible causeRemove the mitochondrial insultAlcohol, medicine, copper deficiency or lead exposure explains the sideroblastic pattern.

1Coordinate safe withdrawal or substitution with the responsible specialty and address alcohol dependence or ongoing occupational exposure without abrupt unsafe changes.
2Replace documented copper or supervised pyridoxine-responsive deficiency and involve toxicology for chelation decisions rather than treating a film appearance.
3Repeat blood counts, reticulocytes and relevant exposure markers to document biological recovery and investigate an additional clonal cause if response is incomplete.

03Chronic clonal diseaseTreat symptoms and progression riskIntegrated marrow assessment establishes sideroblastic myelodysplastic neoplasia.

1Stratify genetic and clinical risk, transfusion burden, erythropoietin level and fitness within a specialist myelodysplasia service.
2Use red-cell support and eligible erythroid treatments such as an erythropoiesis-stimulating agent or luspatercept, with response and thrombosis monitoring.
3Assess iron burden and progression over time, discussing chelation, disease-modifying therapy or transplantation when anticipated benefit outweighs treatment harm.

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

Restores cofactor availability and can substantially improve erythropoiesis in some ALAS2-related or isoniazid-associated disease.

Pyridoxine

A haematologist may supervise an oral therapeutic trial, commonly 50–200 mg daily depending on suspected mechanism, with a defined blood-response review and lowest effective maintenance dose.

Prolonged high-dose exposure can cause sensory neuropathy; document indication, neurological baseline and response rather than continuing an ineffective trial indefinitely.

Corrects copper-deficient haem synthesis and associated neutropenia when malabsorption or excess zinc is addressed.

Copper replacement

Use an oral or intravenous elemental-copper regimen selected by severity and absorption, with specialist monitoring of copper, zinc, counts and neurological response.

Identify and remove the driver, avoid unmonitored over-replacement and recognise that neurological recovery may lag or remain incomplete after blood counts normalise.

Enhances late-stage erythroid maturation and can reduce transfusion burden in selected sideroblastic clonal anaemia.

Luspatercept

Start 1 mg/kg subcutaneously every 3 weeks in an eligible adult, then titrate to 1.33 mg/kg and, if needed, 1.75 mg/kg according to haemoglobin and transfusion response. Stop under the licensed non-response rule after an adequate maximum-dose trial.

Monitor blood pressure, thrombosis, bone pain and haemoglobin rise; discontinue according to non-response rules and do not use outside the defined disease category.

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

Organ iron overload

Absorptive and transfusional iron can cause hepatic fibrosis, cardiomyopathy, diabetes, pituitary dysfunction and arthropathy if burden remains unrecognised.

Transfusion dependence

Persistent ineffective erythropoiesis may require repeated red-cell support, increasing alloimmunisation, reaction and iron-loading risk while complicating future transplantation.

Myeloid progression

Clonal sideroblastic myelodysplasia can acquire excess blasts or evolve to acute myeloid leukaemia, with risk determined by the full genetic and clinical profile.

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

Trend haemoglobin, reticulocytes and transfusion frequency after removing an exposure or starting a targeted erythroid treatment.
Measure ferritin serially and use specialist liver or cardiac MRI when transfusion history and trends suggest clinically important tissue iron.
Repeat copper and zinc during replacement and assess gait, sensation and cognition because neurological improvement can trail haematological correction.
For clonal disease follow platelets, neutrophils, blasts, marrow genetics and constitutional symptoms according to the myelodysplasia risk plan.
During pyridoxine treatment ask about numbness, sensory loss and imbalance and stop or reduce excessive exposure if neuropathy emerges.
Document alcohol, medicine and occupational-source control rather than interpreting a temporary count rise as proof that exposure has ended.

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

Ring is a location

The diagnostic morphology is iron-loaded mitochondria arranged around the erythroblast nucleus, not merely any iron granules within a precursor.

MCV does not classify cause

Congenital, toxic and clonal mechanisms can generate different or mixed cell sizes, so a normal average can conceal two populations.

Copper can mimic MDS

Deficiency causes cytopenia and marrow dysplasia, making surgical and zinc histories crucial before assigning an irreversible clonal diagnosis.

Anaemia can coexist with excess

Ineffective haem synthesis leaves iron unused and may suppress hepcidin, so low haemoglobin must not trigger automatic oral iron.

11Common pitfallsFrequent interpretation and management errors.

01
Prescribing iron for every microcytic sideroblastic anaemia.
02
Calling ordinary sideroblasts pathological ring forms.
03
Missing zinc-driven copper deficiency after surgery.
04
Using basophilic stippling as proof of lead poisoning.
05
Continuing high-dose pyridoxine without response or neuropathy review.