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← Haematology and transfusion indexChapter sections
Purpose and principlesIndications, selection and cautionsMethod and interpretationClinical next stepsRisks, monitoring and follow-upSpecial situationsCommon pitfallsQuestionsSources
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Educational draft · awaiting clinical reviewThe full textbook explains uncertainty but does not replace live national or local guidance, specialist advice, or current prescribing information.

Haemolytic anaemia: investigation

Haematology and transfusion · UK scope · Sources checked 27 Aug 2026 · Clinical review pending

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Time-critical presentation

Suspected thrombotic microangiopathy with thrombocytopenia and schistocytes, acute intravascular haemolysis with haemoglobinuria or kidney injury, a haemolytic transfusion reaction, severe infection-associated haemolysis, or anaemia with shock, chest pain, syncope or heart failure requires same-hour senior haematology and transfusion support. Draw diagnostic and blood-bank samples promptly, but do not delay organ support or a TTP pathway.

Purpose and principles

Confirm accelerated red-cell destruction, separate intravascular from extravascular and immune from non-immune mechanisms, and recognise fragmentation, transfusion reactions and inherited disorders requiring urgent action.

Haemolysis shortens red-cell survival below the marrow's ability to maintain circulating mass. Compensated destruction can present with reticulocytosis, jaundice or gallstones before anaemia; decompensation occurs when destruction accelerates or marrow substrate and reserve are inadequate. History establishes tempo, dark urine, jaundice, back or abdominal pain, fever, bleeding, infection, medicines, foods and chemicals, transfusion, pregnancy, travel, family history and mechanical cardiac devices. Examination assesses physiological compromise, jaundice, splenomegaly, hepatomegaly, ulcers, thrombosis and neurological or renal organ injury.

Core testing establishes destruction and marrow response. Absolute reticulocytes usually rise, indirect bilirubin and LDH increase, and haptoglobin falls as free haemoglobin is bound and cleared. Each marker has limitations: LDH is non-specific, bilirubin depends on liver handling, haptoglobin rises with inflammation and falls in liver disease, and early haemolysis may precede reticulocytosis. The film then supplies mechanism: spherocytes suggest immune or membrane loss, bite and blister cells oxidative damage, fragments mechanical injury or microangiopathy, sickle cells a haemoglobinopathy, and parasites an infection requiring urgent confirmation.

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Haematology and transfusionOriginal SBA

Fragments and falling platelets

An adult has anaemia, thrombocytopenia, schistocytes, raised LDH, confusion and renal impairment. Coagulation results are pending. What is the most appropriate next action?

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Sources and review status4 sources · checked 27 Aug 2026 · clinical review pending+
Sources

Sources and review status

National guidance is shown before implementation-dependent detail. Apply principles in context and verify current guidance when a decision affects care. Source check completed 27 Aug 2026; clinical approval remains outstanding.

  • BSH primary autoimmune haemolytic anaemia guidelineDAT-led immune classification, differential diagnosis and specialist management.
  • BSH TTP and thrombotic microangiopathy guidelineUrgent recognition, ADAMTS13 sampling and treatment pathway for fragmentation syndromes.
  • BNF G6PD deficiency guidanceUK prescribing cautions for medicines that can trigger oxidant haemolysis.
  • NICE NG24 blood transfusion recommendationsClinical transfusion assessment, thresholds and post-unit reassessment.

Editorial contact: Doctor’s Passport editorial team. Source-check date is separate from clinical approval. Report a content problem · Content changes

Authoring stateComplete draftClinical stateAwaiting reviewJurisdictionUnited Kingdom

Classification guides the next test. DAT-positive haemolysis is interpreted by IgG, complement, transfusion and medicine context; DAT-negative haemolysis remains possible in immune and non-immune disease. Intravascular destruction points towards complement, mechanical fragmentation, severe oxidative injury, infection or incompatible transfusion, whereas extravascular clearance is typical of warm antibody, membrane and some haemoglobin disorders. Specialist enzyme, membrane, haemoglobin, flow, infectious, complement and genetic assays should be collected with timing and recent transfusion considered.

Key points

  • Confirm haemolysis with a pattern, not a solitary LDH: falling haemoglobin, raised absolute reticulocytes, unconjugated bilirubin and LDH, reduced haptoglobin and supportive film findings should be reconciled with timing and liver function.
  • A low reticulocyte response does not exclude dangerous haemolysis early in the episode or when infection, marrow disease, renal failure, iron, B12 or folate deficiency limits compensation.
  • The direct antiglobulin test detects immunoglobulin or complement on red cells; it supports immune classification but does not by itself prove that active haemolysis is occurring.
  • Schistocytes with thrombocytopenia and organ injury raise thrombotic microangiopathy, disseminated coagulation or mechanical fragmentation and demand urgent clinical context rather than a routine outpatient haemolysis screen.
  • Spherocytes occur in warm immune haemolysis and hereditary spherocytosis. DAT, family history, MCHC, splenomegaly and specialist membrane testing distinguish them.
  • Separate intravascular clues, such as haemoglobinaemia, haemoglobinuria, very low haptoglobin and renal injury, from extravascular jaundice, splenomegaly and macrophage-mediated clearance; overlap is common.
  • Always review recent transfusion, pregnancy, medicines, infection, travel, prosthetic valves, burns, family and ethnic background and episodic triggers before selecting specialised tests.

Indications, selection and cautions

Biochemical destruction pattern

Falling haemoglobin with reticulocytosis, indirect bilirubin and LDH rise, low haptoglobin and polychromasia supports haemolysis when alternative sources are considered.

Intravascular haemolysisRed flag

Dark urine, haemoglobinaemia or haemoglobinuria, markedly consumed haptoglobin, renal injury and rapid symptoms indicate free haemoglobin released within the circulation.

Extravascular haemolysis

Jaundice, splenomegaly, spherocytes and a more chronic course suggests macrophage clearance in spleen and liver, although intravascular overlap can occur.

Thrombotic microangiopathyRed flag

Schistocytes, thrombocytopenia, neurological, renal, cardiac or gastrointestinal injury and biochemical haemolysis requires urgent TTP and secondary-microangiopathy assessment.

Haemolytic transfusion reactionRed flag

Fever, chills, pain, dyspnoea, hypotension, dark urine or unexpected haemoglobin fall during or after transfusion requires immediate transfusion-reaction management.

Inherited episodic pattern

Childhood or family jaundice, gallstones, neonatal disease or attacks after infection, oxidant exposure or fava beans suggests a membrane, enzyme or haemoglobin disorder.

Method and interpretation

  1. 01
    FBC, absolute reticulocytes and serial haemoglobinFirst step
    Why
    Quantify anaemia, compensation and tempo across all lineages.
    Interpretation and limitations
    Reticulocytosis supports regeneration but may be absent early or with nutrient, renal or marrow limitation. Thrombocytopenia raises microangiopathy, consumption or hypersplenism; other cytopenias broaden the differential.
  2. 02
    Bilirubin, LDH and haptoglobin
    Why
    Demonstrate increased red-cell breakdown and free-haemoglobin clearance.
    Interpretation and limitations
    A concordant indirect bilirubin and LDH rise with low haptoglobin supports haemolysis. Interpret liver disease, inflammation, tissue injury and ineffective erythropoiesis before assigning specificity.
  3. 03
    Peripheral blood film
    Why
    Identify morphology that classifies mechanism and urgency.
    Interpretation and limitations
    Schistocytes demand urgent microangiopathy context; spherocytes suggest immune or hereditary membrane disease; bite and blister cells support oxidant injury; parasites, sickling, agglutination and polychromasia guide focused tests.
  4. 04
    Direct antiglobulin test
    Why
    Detect red-cell-bound IgG and complement and support immune classification.
    Interpretation and limitations
    Interpret monospecific findings with active haemolysis, transfusion, medicines and cold exposure. A positive result without destruction is not AIHA, and a negative result does not exclude every immune mechanism.

Clinical next steps

01Unstable or fragmentedAct on organ-threatening haemolysisFirst stepThere is shock, severe symptomatic anaemia, haemoglobinuria with kidney injury, thrombocytopenia with fragments, or a suspected transfusion reaction.+
  1. 1Use ABCDE, stop any transfusion, maintain venous access, check identity and send urgent FBC, film, reticulocytes, haemolysis, renal, coagulation, group and blood-bank reaction samples while supporting circulation and urine output.
  2. 2PreferredThe preferred emergency route is immediate senior haematology and transfusion discussion, with a TTP pathway for high-probability microangiopathy and the local transfusion-reaction pathway for temporally related haemolysis.
  3. 3EscalationEscalate neurological, renal, cardiac or respiratory compromise to critical care and give compatible red cells for threatened oxygen delivery without waiting for every specialised result.
02

Risks, monitoring and follow-up

  • Trend haemoglobin and absolute reticulocytes to distinguish continuing destruction from marrow recovery or developing underproduction.
  • Follow bilirubin, LDH, haptoglobin, urine colour, renal function and potassium during significant intravascular haemolysis, using clinical improvement rather than one marker alone.
  • Monitor platelets, neurological, cardiac and renal status closely in any microangiopathic pattern and follow the specialist ADAMTS13 and treatment pathway.
  • After transfusion-associated haemolysis, ensure reaction investigation, haemovigilance reporting, antibody documentation and future compatibility advice are completed.
  • Repeat inherited-disease testing when acute haemolysis, reticulocytosis or recent transfusion makes the initial assay unreliable, with timing agreed by haematology and the laboratory.
  • Record gallstones, splenomegaly, thrombosis, iron burden and folate need in chronic haemolytic disorders through the diagnosis-specific follow-up plan.

Special situations

LDH is not a haemolysis test alone

Liver, muscle, tumour, infarction and ineffective erythropoiesis also raise LDH. Reticulocytes, bilirubin, haptoglobin and film establish coherence.

DAT detects coating, not consequence

Red cells can carry immunoglobulin or complement without clinically important destruction, particularly after transfusion or medicine exposure.

Ineffective erythropoiesis mimics destruction

Severe B12 or folate deficiency releases LDH and bilirubin within marrow but produces an inappropriately low reticulocyte response.

Haemoglobinuria has competitors

A urine dipstick detects haem pigment. Microscopy distinguishes few red cells in haemoglobinuria or myoglobinuria from true haematuria.

Timing changes inherited assays

Reticulocytes, donor cells and selective destruction of vulnerable red cells can make an enzyme result appear healthier during an acute episode.

Common pitfalls

  1. 01

    Calling haemolysis from an isolated raised LDH.

  2. 02

    Assuming a positive DAT proves active autoimmune haemolysis.

  3. 03

    Waiting for ADAMTS13 before escalating a high-probability TTP phenotype.

  4. 04

    Missing a transfusion reaction because symptoms begin after the unit finishes.

  5. 05

    Ignoring low reticulocytes in early haemolysis or mixed marrow deficiency.

  6. 06

    Accepting a normal acute G6PD assay despite a convincing oxidative episode.

  7. 07

    Failing to document responsibility for specialised results sent before discharge.

  • G6PD activity can be falsely reassuring during or soon after an acute episode because older deficient cells have been destroyed and transfused or reticulocyte-rich blood is over-represented; repeat later if suspicion remains.
  • 05
    Urinalysis, renal function and electrolytes
    Why
    Detect haemoglobinuria and organ effects of intravascular destruction.
    Interpretation and limitations
    Blood-positive urine with few red cells suggests pigment, while rising creatinine or potassium increases urgency. Myoglobin and true haematuria remain alternatives requiring microscopy and context.
  • 06
    Coagulation, ADAMTS13 and microangiopathy tests
    Why
    Differentiate TTP, disseminated coagulation and secondary thrombotic microangiopathy.
    Interpretation and limitations
    Send pretreatment ADAMTS13 when feasible, but a high clinical probability of TTP activates the emergency pathway without waiting. PT, APTT, fibrinogen and D-dimer support consumptive coagulation assessment.
  • 07
    G6PD, membrane and haemoglobin studies
    Why
    Identify inherited enzyme, membrane or haemoglobin causes after phenotype review.
    Interpretation and limitations
    Select with haematology and account for ethnicity, family history, reticulocytosis and transfusion. Repeat G6PD testing after recovery when an acute result conflicts with a convincing oxidative episode.
    • Confirm and classifyBuild a concordant haemolysis patternAnaemia, jaundice, reticulocytosis, dark urine or an abnormal film raises red-cell destruction in a stable patient.
    +
    1. 1First lineFirst-line tests are FBC, absolute reticulocytes, film, bilirubin, LDH, haptoglobin, DAT, renal and liver profile, urinalysis and a careful transfusion, medicine, infection and family history.
    2. 2AlternativeClassify intravascular versus extravascular and immune versus non-immune using DAT and morphology; an alternative diagnosis is ineffective B12 or folate erythropoiesis when LDH is high but reticulocytes remain low.
    3. 3EscalationEscalate an inconsistent pattern to repeat sampling and laboratory or haematology review rather than labelling haemolysis from one non-specific marker.
    03Define causeSelect specialised testing at the right timeHaemolysis is supported and emergency causes have been addressed.+
    1. 1Use DAT specificity and transfusion timing for immune disease; use enzyme assays, membrane testing, haemoglobin analysis, infection studies, cardiac-device review and genetics according to film and history.
    2. 2PreferredAlternativeFor suspected oxidative haemolysis, the preferred strategy records the trigger and obtains G6PD activity, with repeat testing after recovery as an alternative when acute reticulocytosis or transfusion could mask deficiency.
    3. 3Coordinate treatment samples before steroids, plasma exchange or transfusion when safe, then document the working mechanism, pending tests and named clinician responsible for results.