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← Haematology and transfusion indexChapter sections
Purpose and principlesIndications, selection and cautionsMethod and interpretationClinical next stepsProcedure and medicine safetyRisks, 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.

Peripheral blood film patterns

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

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Time-critical presentation

Blasts or abnormal promyelocytes, schistocytes with thrombocytopenia and organ symptoms, intracellular malaria parasites in an unwell traveller, or overwhelming sepsis morphology requires immediate clinical and specialist action. The film should accelerate treatment and definitive sampling, not become a reason to wait for a perfect classification.

Purpose and principles

Use blood-film morphology to verify automated counts, recognise time-critical haematological patterns and direct confirmatory testing without turning a descriptive cell shape into a final diagnosis.

A peripheral blood film is a targeted extension of the full blood count. It can confirm whether an automated result is genuine, show whether several lineages are morphologically abnormal and identify patterns that alter the speed and sequence of care. Pre-analytical quality matters: delay, incorrect anticoagulant ratio, poor smear preparation and temperature can distort cells. The report therefore describes what is seen and recommends correlation, while the clinician decides whether the pattern represents deficiency, destruction, inflammation, infection, marrow stress or clonal disease.

Red-cell review asks about size, colour, variation, shape, inclusions and arrangement. Polychromasia usually reflects reticulocytosis; macro-ovalocytes and hypersegmented neutrophils support megaloblastic change; bite or blister cells can accompany oxidant injury; basophilic stippling has toxic, haemoglobinopathy and marrow associations. Rouleaux suggests increased plasma proteins, whereas true agglutination may distort automated indices and support a cold-reactive process. No single morphology should override haematinics, haemolysis markers, electrophoresis, direct antiglobulin testing or clinical history.

Indications, selection and cautions

Microangiopathic patternRed flag

Schistocytes with falling haemoglobin, thrombocytopenia, high LDH and low haptoglobin indicate fragmentation. Neurological, renal or cardiac involvement increases urgency for a thrombotic-microangiopathy pathway.

Acute leukaemia patternRed flag

Circulating blasts, Auer rods or abnormal promyelocytes may accompany anaemia, thrombocytopenia and infection or bleeding. Prompt expert morphology, flow, genetics and coagulation assessment is required.

Megaloblastic pattern

Macro-ovalocytes, anisopoikilocytosis and hypersegmented neutrophils support impaired DNA synthesis from B12, folate, medicines or marrow disease; neurological features prioritise urgent B12 assessment.

Haemolytic shape pattern

Spherocytes, bite cells, blister cells, polychromasia or agglutination direct immune, enzyme, membrane and cold-reactive testing but require biochemical confirmation of active haemolysis.

Marrow-infiltration pattern

Nucleated red cells, immature myeloid forms, teardrops and abnormal platelets form a leucoerythroblastic picture that can reflect fibrosis, metastatic infiltration or severe marrow stress.

Blood-borne infectionRed flag

Malaria parasites or other visible organisms in a compatible traveller can establish an urgent infectious diagnosis, but species, parasitaemia and repeat sampling follow specialist protocols.

Method and interpretation

  1. 01
    Expert peripheral-film reviewFirst step
    Why
    Confirm morphology, estimate abnormal-cell burden and issue time-critical alerts.
    Interpretation and limitations
    The laboratory integrates automated flags and manual morphology. An urgent verbal report for blasts, promyelocytes, schistocytes or parasites requires documented clinical receipt and action rather than passive electronic acknowledgement.
  2. 02
    Reticulocytes, bilirubin, LDH and haptoglobin
    Why
    Confirm whether a red-cell shape pattern represents active haemolysis and marrow response.
    Interpretation and limitations
    Reticulocytosis with indirect hyperbilirubinaemia, raised LDH and low haptoglobin supports haemolysis. Deficiency, renal disease or marrow suppression can blunt reticulocytes, and haptoglobin may be raised by inflammation.
  3. 03
    Direct antiglobulin test
    Why
    Identify immunoglobulin or complement coating when immune haemolysis is plausible.
    Interpretation and limitations
    A positive result supports immune red-cell coating but requires strength, specificity, transfusion and medicine context. Spherocytes with a negative test raises hereditary membrane disease or DAT-negative immune haemolysis.
  4. 04
    Flow cytometry and acute-leukaemia genetics
    Why
    Define lineage, maturation and disease-specific molecular features after abnormal cells are seen.
    Interpretation and limitations

Clinical next steps

01FragmentationSeparate TMA from other fragmentationFirst stepSchistocytes accompany anaemia, thrombocytopenia or new renal, neurological, cardiac or bleeding features.+
  1. 1First linePreferredPreferred first-line assessment is urgent repeat FBC, reticulocytes, LDH, bilirubin, haptoglobin, renal profile, urinalysis, coagulation, blood pressure and direct antiglobulin testing, with expert film confirmation.
  2. 2EscalationIf TTP is plausible, send pre-plasma ADAMTS13 and escalate immediately to the regional TTP service; do not wait for a historical pentad or the activity result before specialist treatment decisions.
  3. 3AlternativeEscalationAlternative causes include DIC, malignant hypertension, mechanical valves and severe burns; use coagulation, clinical context and organ pattern, escalating unresolved microangiopathic haemolysis to haematology.

Procedure and medicine safety

Induces promyelocyte differentiation and reduces early haemorrhagic risk while molecular confirmation and definitive APL treatment are coordinated.

Tretinoin (all-trans retinoic acid) for suspected APL

Start 45 mg/m² per day by mouth in two divided doses immediately on morphological suspicion, under the acute-leukaemia protocol, without waiting for genetic confirmation.

Specialist-only treatment is highly teratogenic and can cause differentiation syndrome, leukocytosis, hepatic toxicity and hyperlipidaemia. Monitor coagulation and fibrinogen closely; if differentiation syndrome is suspected, start protocol dexamethasone, commonly 10 mg intravenously every 12 hours, immediately.

Risks, monitoring and follow-up

  • Trend the full blood count and haemolysis markers when morphology represents an evolving destructive or marrow process.
  • In suspected APL or DIC, monitor platelets, PT, APTT, fibrinogen, D-dimer and clinical bleeding at the specialist-directed frequency.
  • For a clonal or blast population, confirm that flow, genetics and marrow samples reached the correct laboratory and have a named results owner.
  • For malaria, follow species-specific parasitaemia and clinical monitoring through the infectious-disease protocol until clearance criteria are met.
  • Repeat morphology only when it answers trajectory or treatment response; do not substitute serial films for the definitive molecular, immune or marrow test.

Special situations

Schistocytes name a mechanism

Fragmented cells show mechanical injury, not one disease. Platelets, coagulation, blood pressure, devices and organ pattern separate TTP, DIC and other causes.

Rouleaux is not agglutination

Coin-stack rouleaux disperses differently from antibody-mediated clumping. Plasma proteins suggest myeloma or inflammation, whereas cold agglutination can distort automated red-cell indices.

Teardrops need context

Numerous teardrops with leucoerythroblastosis supports marrow distortion, but occasional poorly formed cells may be artefactual. Distribution and accompanying immature cells matter.

Reactive cells can look alarming

Viral infection can produce large atypical lymphocytes with abundant cytoplasm. Population heterogeneity and clinical setting help distinguish them from a monomorphic clone.

Film timing changes yield

Transfusion, corticosteroids and treatment can alter circulating morphology. Capture diagnostic blood before intervention when safe, but never delay emergency care to preserve a specimen.

Common pitfalls

  1. 01

    Equating schistocytes with TTP without demonstrating haemolysis or considering DIC and mechanical causes.

  2. 02

    Calling spherocytes autoimmune haemolysis without a direct antiglobulin test and family history.

  3. 03

    Delaying acute-leukaemia escalation until every blast has been classified.

  4. 04

    Interpreting one target cell or teardrop as a definitive disease label.

  5. 05

    Missing platelet clumps on the film and treating pseudothrombocytopenia.

  6. 06

    Assuming a negative initial malaria film excludes infection despite strong epidemiological and clinical suspicion.

Practice

Two practice questions

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Question 1 of 2
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Haematology and transfusionOriginal SBA

Fragmented cells with normal coagulation

An adult has confusion, platelets 18 × 10⁹/L, anaemia, raised LDH, low haptoglobin and schistocytes. PT and APTT are not prolonged. Which action is most appropriate?

Choose one answer, then submit
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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. Typical adult dose examples remain subject to patient factors, contraindications and the live BNF or specialist protocol. Source check completed 27 Aug 2026; clinical approval remains outstanding.

  • BSH thrombotic microangiopathy guidelineSchistocyte-associated TTP recognition, ADAMTS13 sampling and urgent regional care.
  • BSH autoimmune haemolytic anaemia guidelineFilm, DAT and immune-haemolysis interpretation.
  • UKHSA malaria diagnosis and treatment guidanceUK diagnostic films, parasitaemia and urgent treatment pathway.
  • BSH acute promyelocytic leukaemia guidelineRecognition and emergency management of suspected APL.

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
White-cell and platelet review is often more urgent. Toxic granulation and vacuolation support intense reactive change but do not identify an organism. Left shift can accompany infection or myeloid disease. Blasts, Auer rods, abnormal promyelocytes or a monomorphic lymphoid population require laboratory and haematology communication. Giant platelets may indicate increased turnover or an inherited disorder, while clumping can explain a spurious count. A useful film interpretation finishes with the decisive next sample or action and states uncertainty explicitly.

Key points

  • Read the film alongside the full blood count, reticulocytes, clinical question and sampling history. Morphology without the numerical and clinical context is vulnerable to over-interpretation.
  • Start at low power for distribution, rouleaux, agglutination, large abnormal cells and platelet clumps, then use higher power for red-cell shape, white-cell maturation, inclusions and platelet morphology.
  • Schistocytes indicate mechanical fragmentation but are not synonymous with TTP; thrombocytopenia, haemolysis, renal, neurological and coagulation findings decide the thrombotic-microangiopathy or DIC pathway.
  • Spherocytes support extravascular red-cell membrane loss and occur in warm autoimmune haemolysis and hereditary spherocytosis. The direct antiglobulin test and family or transfusion history discriminate.
  • Target cells occur with haemoglobinopathy, liver disease, iron deficiency and hyposplenism; teardrops plus a leucoerythroblastic picture raise marrow fibrosis or infiltration but can have other causes.
  • Blasts require urgent expert classification. Abnormal promyelocytes with bleeding or coagulation disturbance raises acute promyelocytic leukaemia, for which specialist treatment is time critical.
  • Reactive lymphocytes can accompany viral infection, while a monotonous small-lymphocyte population suggests a clonal process. Flow cytometry answers lineage and clonality when indicated.
Send samples after laboratory or haematology discussion so the correct anticoagulant and panels are used. Morphology initiates the pathway; flow and genetics refine classification and treatment.
  • 05
    Coagulation screen and fibrinogen
    Why
    Detect consumptive coagulopathy when promyelocytes, sepsis or fragmentation raises DIC concern.
    Interpretation and limitations
    Prolonged clotting times, falling fibrinogen, raised D-dimer and thrombocytopenia support consumption, but early APL-related coagulopathy can evolve quickly and needs serial monitoring.
  • 06
    Malaria films and rapid testing
    Why
    Confirm species and quantify parasitaemia in a compatible febrile traveller.
    Interpretation and limitations
    Follow UKHSA and infectious-disease laboratory pathways, repeat films if suspicion remains and the first is negative, and treat severe malaria without avoidable delay after diagnostic sampling.
    • 02BlastsActivate the acute-leukaemia pathwayBlasts, Auer rods or abnormal promyelocytes are reported or strongly suspected.+
    1. 1Assess bleeding, infection, leukostasis symptoms and haemodynamics; obtain coagulation, fibrinogen, renal, electrolyte and urate samples while contacting haematology urgently.
    2. 2PreferredThe preferred diagnostic route is coordinated morphology, flow cytometry, cytogenetics and molecular testing from correctly handled blood and marrow samples; avoid empirical corticosteroids before lineage sampling unless specialist-led.
    3. 3EscalationEscalate suspected APL with bleeding or coagulopathy as a same-hour emergency; specialist-led all-trans retinoic acid and fibrinogen- and platelet-directed support should begin on morphological suspicion without waiting for complete genetic confirmation.
    03Non-urgent morphologyConvert a pattern into a focused work-upThe film shows macro-ovalocytes, target cells, spherocytes, teardrops, rouleaux or reactive lymphocytes without immediate physiological danger.+
    1. 1Correlate the morphology with indices, absolute counts, reticulocytes, medicines, alcohol, liver, renal, infection, family and transfusion history rather than assigning a diagnosis from shape alone.
    2. 2PreferredConfirmatoryChoose the preferred confirmatory test for the leading mechanism: haematinics for megaloblastosis, DAT for immune coating, electrophoresis for haemoglobinopathy, immunoglobulins for rouleaux or flow for persistent monomorphic lymphocytosis.
    3. 3EscalationIf initial tests conflict with progressive cytopenia, splenomegaly or constitutional symptoms, escalate to haematology and consider marrow examination instead of repeated descriptive films.
    A negative or non-specific film does not exclude serious disease. Early haemolysis, marrow disease and infection may need serial counts, biochemical tests, cultures, flow or marrow assessment.