Haematology: Emergencies

• Basics: At a Glance
• Bleeding: Major Haemorrhage | Life-threatening Bleeding on Anticoagulants | Disseminated Intravascular Coagulation | Severe Thrombocytopenia with Bleeding
• Thrombotic microangiopathy: Thrombotic Thrombocytopenic Purpura | Haemolytic Uraemic Syndrome
• White cells and marrow: Suspected Acute Leukaemia | Hyperleukocytosis and Leukostasis | Drug-induced Agranulocytosis | Haemophagocytic Lymphohistiocytosis
• Red cells: Acute Severe Haemolysis | Sickle Cell Emergencies | Severe Malaria | Methaemoglobinaemia | Hyperviscosity Syndrome
• Other: HIT and Catastrophic Thrombosis | Overwhelming Post-splenectomy Infection | Severe Transfusion Reactions
• Revision: Drug Reference Table | Spot the Emergency | Exam-style Scenarios | Key Points | Guidelines and Further Reading

🚨 Haematological emergencies often look like something else at first - a bleed, sepsis, confusion, or kidney injury. A full blood count, blood film and clotting screen frequently give the answer within an hour. Neutropenic sepsis and tumour lysis syndrome are covered in the Oncological Emergencies chapter.
Your four questions for every patient: Is the patient bleeding, clotting, or both? What does the blood film show (blasts, schistocytes, sickle cells, parasites)? Who needs to be called now - haematology, blood bank, ICU? Which treatment must not wait for confirmation?

At a Glance

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Major Haemorrhage

Definition: Bleeding that causes shock (heart rate over 110, systolic BP under 90), or needs large volumes of blood (e.g. more than 4 units in an hour, or 10 units in 24 hours). Common causes: trauma, GI bleeding, obstetric haemorrhage, surgery, ruptured aneurysm.

Immediate actions (local major haemorrhage protocol, BSH guidance):

• Call for help and activate the major haemorrhage protocol (one phone call to the blood bank with a clear message).
• Stop the bleeding - pressure, tourniquets, surgery, endoscopy, interventional radiology, obstetric measures.
• Tranexamic acid 1 g IV over 10 minutes (then 1 g over 8 hours) - in trauma within 3 hours and obstetric haemorrhage. Not in GI bleeding (no benefit, more clots).
• Two large-bore IV cannulas; send samples (FBC, clotting, fibrinogen, group and cross-match, U&E, calcium, lactate, blood gas).
• Blood:
  • Emergency group O red cells (O RhD negative for women of childbearing age; O positive for men and older women) until group-specific blood is available.
  • In trauma, give red cells and FFP in about a 1:1 ratio early.
• Avoid large volumes of crystalloid - it dilutes clotting factors.
• In trauma, aim for permissive hypotension (systolic about 80–90) until bleeding is controlled - except in head injury.

Targets (guided by repeated tests or viscoelastic testing such as ROTEM or TEG):

• Hb 70–90 g/L.
• Platelets over 50 × 10⁹/L (over 100 in head injury or ongoing major bleeding).
• PT and APTT under 1.5 times normal.
• Fibrinogen over 1.5 g/L (over 2 g/L in obstetric haemorrhage) - give cryoprecipitate or fibrinogen concentrate.
• Ionised calcium over 1.0 mmol/L (citrate in blood products lowers calcium).
• Temperature over 36 °C - warm fluids and the patient.
• Avoid acidosis.

Lethal triad: Hypothermia, acidosis and coagulopathy all make bleeding worse.

Stand down the protocol when bleeding is controlled; then consider VTE prophylaxis once safe.

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Life-threatening Bleeding on Anticoagulants

• Stop the anticoagulant; record the drug, dose and time of the last dose; check kidney function and clotting.
• Warfarin: Prothrombin complex concentrate (PCC, e.g. 25–50 units/kg) plus IV vitamin K 5–10 mg. Recheck the INR after PCC.
• Dabigatran: Idarucizumab 5 g IV. Haemodialysis is an option.
• Apixaban or rivaroxaban:
  • Andexanet alfa for life-threatening GI bleeding (NICE TA697).
  • Otherwise PCC (e.g. 50 units/kg).
  • Oral activated charcoal if the last dose was within 2–6 hours.
• Edoxaban: PCC.
• Unfractionated heparin: Protamine (1 mg per 100 units given in the last 2 hours; maximum 50 mg). Partial reversal of LMWH.
• Thrombolysis (alteplase): Cryoprecipitate and tranexamic acid.
• Antiplatelets: Platelet transfusion only in selected cases (e.g. before neurosurgery).
• Intracranial haemorrhage - reverse urgently and control BP (see the Stroke chapter).

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Disseminated Intravascular Coagulation

What it is: Widespread activation of clotting, which uses up platelets and clotting factors. This causes bleeding and clotting at the same time. It is always secondary to something else.

Causes:

• Sepsis (the commonest).
• Trauma, burns, major surgery.
• Obstetric - placental abruption, amniotic fluid embolism, severe pre-eclampsia, retained products.
• Cancer - APL, mucin-secreting adenocarcinomas (pancreas, prostate, stomach).
• Severe liver failure.
• Snake bites; ABO transfusion reaction; heat stroke; pancreatitis.

Features:

• Bleeding from cannula sites, wounds, gums; bruising.
• Organ failure from small clots (kidney, lung, skin necrosis, purpura fulminans).

Blood tests:

• Low platelets (or falling).
• Prolonged PT and APTT.
• Low fibrinogen.
• High D-dimer.
• Schistocytes.
• The ISTH score helps diagnosis.

Treatment:

• Treat the cause - antibiotics and source control, delivery, ATRA in APL.
• Blood products if bleeding or before procedures:
  • Platelets (keep over 50 if bleeding).
  • FFP.
  • Cryoprecipitate to keep fibrinogen over 1.5 g/L.
• Don't give products just to correct numbers in a patient who isn't bleeding.
• Heparin (therapeutic dose) when thrombosis dominates (e.g. purpura fulminans, chronic DIC with cancer) - specialist decision.
• VTE prophylaxis in non-bleeding patients.

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Severe Thrombocytopenia with Bleeding

• Check the film first - schistocytes (TTP, DIC), blasts (leukaemia), clumping (false low).
• Platelets under 10 × 10⁹/L, or any count with significant bleeding - urgent haematology advice.
• ITP with life-threatening bleeding:
  • IVIg 1 g/kg (repeat the next day).
  • IV methylprednisolone 1 g.
  • Platelet transfusion (short-lived but can help).
  • Tranexamic acid.
  • TPO receptor agonists; emergency splenectomy rarely.
• Marrow failure (chemotherapy, leukaemia) - platelet transfusion.
• Avoid platelets in TTP and HIT unless bleeding is life-threatening.
• Stop antiplatelets, NSAIDs and anticoagulants where possible; avoid IM injections.
• Intracranial bleeding with low platelets - keep platelets over 100.

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Thrombotic Thrombocytopenic Purpura

What it is: A severe deficiency of ADAMTS13 (usually from autoantibodies; rarely inherited). Without it, huge von Willebrand factor multimers build up, causing platelet clots in small vessels throughout the body. Untreated mortality is about 90%.

Who:

• Adults 20–50, more often women.
• Commoner in Black people.
• Triggers include pregnancy, infection, HIV, and drugs (ticlopidine, clopidogrel rarely, quinine).

Features (the full "pentad" is uncommon):

• Thrombocytopenia (often under 30 × 10⁹/L) with bruising or purpura.
• Microangiopathic haemolytic anaemia - schistocytes, high LDH, low haptoglobin, high reticulocytes, DAT negative.
• Neurological symptoms - headache, confusion, stroke-like episodes, seizures, coma (often fluctuating).
• Kidney involvement (usually mild, unlike HUS).
• Fever.
• Abdominal pain; raised troponin (cardiac involvement - a poor sign).

Diagnosis:

• Schistocytes plus low platelets - treat as TTP until proven otherwise.
• ADAMTS13 activity under 10% confirms it (send before plasma exchange; results may take days).
• The PLASMIC score estimates probability.
• Normal clotting (unlike DIC).

Treatment (same day, at a TTP centre):

• Urgent plasma exchange - the key treatment (replaces ADAMTS13 and removes antibodies). If there is a delay, give FFP.
• Steroids - IV methylprednisolone.
• Caplacizumab - blocks von Willebrand factor–platelet binding (faster platelet recovery, fewer relapses; increases bleeding).
• Rituximab - reduces the antibody and prevents relapse.
• Don't give platelet transfusions unless there is life-threatening bleeding (they can worsen clotting).
• Folic acid; aspirin and LMWH prophylaxis once platelets recover above 50.
• Long-term ADAMTS13 monitoring to detect relapse (pre-emptive rituximab).

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Haemolytic Uraemic Syndrome

• What it is: A thrombotic microangiopathy mainly affecting the kidneys - the triad of MAHA, low platelets and AKI.
• STEC-HUS (typical - about 90%):
  • Follows bloody diarrhoea from Shiga toxin-producing E. coli (e.g. O157:H7) - undercooked meat, farm visits, unpasteurised milk.
  • Mainly children under 5 and older people.
  • Develops 5–10 days after diarrhoea starts.
  • Treatment: Supportive - fluids, careful electrolyte management, dialysis if needed, transfusion.
  • Avoid antibiotics and antimotility drugs in suspected STEC diarrhoea (they may increase toxin release).
  • Notifiable; public health follow-up.
• Atypical HUS (complement-mediated):
  • No preceding diarrhoea; often familial (complement gene mutations) or triggered by pregnancy, infection, transplant or drugs.
  • Severe kidney failure; relapses.
  • Complement inhibitors - eculizumab or ravulizumab (with meningococcal vaccination and antibiotic cover).
  • Plasma exchange while awaiting results.
• Secondary causes of TMA:
  • Malignant hypertension.
  • Scleroderma renal crisis.
  • Pregnancy (HELLP).
  • Drugs - gemcitabine, calcineurin inhibitors, VEGF inhibitors, quinine.
  • Stem cell transplant.
  • Pneumococcal infection (children).

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Suspected Acute Leukaemia

• Clues:
  • Pancytopenia or a very high white count with blasts on the film.
  • Bruising and infections over a few weeks.
  • Bone pain (children); gum swelling.
• Same-day haematology referral.
• Look for immediate threats:
  • DIC and bleeding (especially APL) - check clotting and fibrinogen.
  • Neutropenic sepsis - antibiotics within 1 hour.
  • Leukostasis (see below).
  • Tumour lysis syndrome - potassium, phosphate, urate, calcium, creatinine.
  • Mediastinal mass (T-ALL) - airway compression; avoid lying flat and sedation.
• APL suspected (bleeding, low fibrinogen, abnormal promyelocytes) - start ATRA immediately.
• Start hydration and allopurinol (or rasburicase if high risk).
• Avoid unnecessary invasive procedures until clotting is corrected.

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Hyperleukocytosis and Leukostasis

• What it is: A very high white count (usually blasts over 100 × 10⁹/L - lower in AML) makes the blood "sludge" in small vessels.
• Who: AML (especially monocytic types) and ALL; rarely CML or CLL (CLL tolerates very high counts).
• Features:
  • Lungs - breathlessness, hypoxia, infiltrates.
  • Brain - headache, confusion, visual changes, stroke, intracranial haemorrhage.
  • Priapism; limb ischaemia; MI.
• Lab pitfalls:
  • Pseudohyperkalaemia and falsely low oxygen on blood gases (cells use up oxygen in the syringe) - check with pulse oximetry.
  • Falsely low glucose.
• Treatment:
  • IV fluids.
  • Start cytoreduction quickly - hydroxycarbamide or induction chemotherapy.
  • Leukapheresis in selected cases.
  • Avoid red cell transfusion (it raises viscosity) unless essential.
  • Platelets to keep over 30–50 (bleeding risk).
  • TLS prevention (rasburicase).

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Drug-induced Agranulocytosis

• What it is: A sudden severe fall in neutrophils (often under 0.1 × 10⁹/L) caused by a drug.
• Common culprits:
  • Carbimazole and propylthiouracil.
  • Clozapine.
  • Sulfasalazine.
  • Co-trimoxazole; dapsone.
  • Deferiprone.
  • Metamizole (dipyrone - used abroad).
  • Some antiepileptics.
• Features: Sore throat, mouth ulcers, fever, sepsis.
• Action:
  • Urgent FBC in anyone on these drugs with a sore throat or fever - patients should be warned about this.
  • Stop the drug immediately and permanently.
  • Treat as neutropenic sepsis (IV antibiotics within 1 hour).
  • G-CSF may speed recovery.
  • Report via Yellow Card; record the allergy.

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Haemophagocytic Lymphohistiocytosis

• What it is: A life-threatening "cytokine storm" from uncontrolled immune activation; macrophages engulf blood cells.
• Triggers:
  • Infection (EBV, CMV, HIV, TB, leishmaniasis).
  • Lymphoma (especially T-cell).
  • Autoimmune disease - called macrophage activation syndrome in Still's disease or SLE.
  • Immunotherapy and CAR-T.
  • Inherited forms in children.
• Features:
  • Persistent high fever.
  • Splenomegaly.
  • Cytopenias.
  • Very high ferritin (often over 10,000 µg/L).
  • High triglycerides, low fibrinogen.
  • Liver dysfunction; rash; neurological symptoms.
  • Multi-organ failure.
• Diagnosis: HLH-2004 criteria or the HScore; raised soluble CD25; haemophagocytosis on marrow (not essential).
• Treatment (urgent, specialist):
  • High-dose steroids (dexamethasone).
  • Anakinra, IVIg, etoposide.
  • Treat the trigger.
  • ICU support.
• Think of HLH in "sepsis" that doesn't respond to antibiotics, with very high ferritin and falling counts.

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Acute Severe Haemolysis

• Features: Sudden anaemia, jaundice, dark urine (haemoglobinuria), back or abdominal pain, AKI, shock.
• Causes to consider urgently:
  • ABO-incompatible transfusion.
  • G6PD deficiency crisis (drugs, infection, fava beans).
  • Warm AIHA (rapid onset).
  • Severe falciparum malaria ("blackwater fever").
  • TTP or HUS.
  • PNH.
  • Clostridium perfringens sepsis.
  • Snake venom; burns.
• Tests:
  • FBC, film, reticulocytes, LDH, bilirubin, haptoglobin.
  • DAT.
  • Malaria testing in anyone who has travelled.
  • U&E, potassium (raised by haemolysis), clotting.
  • Urine dipstick (blood positive without red cells on microscopy).
• Treatment:
  • Treat the cause.
  • IV fluids to protect the kidneys.
  • Transfusion as needed (with blood bank advice in AIHA).
  • Folic acid.
  • Steroids for warm AIHA.
  • Stop oxidant drugs in G6PD deficiency.
  • Monitor potassium.

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Sickle Cell Emergencies

Full details are in the Haemoglobinopathies and Transfusion chapter. The key emergencies:

• Acute pain crisis - strong analgesia within 30 minutes; reassess every 30 minutes.
• Acute chest syndrome - new infiltrate with chest symptoms or hypoxia: oxygen, antibiotics, incentive spirometry, top-up or exchange transfusion, early ICU.
• Stroke - urgent exchange transfusion (HbS under 30%).
• Splenic sequestration - rapidly enlarging spleen and falling Hb - urgent transfusion.
• Aplastic crisis (parvovirus) - low reticulocytes; transfuse.
• Sepsis (hyposplenism) - IV antibiotics urgently for fever over 38 °C.
• Priapism over 4 hours - urology emergency.
• Hyperhaemolysis after transfusion - Hb below the pre-transfusion level; avoid further transfusion; steroids and IVIg (specialist).

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Severe Malaria

• Think of malaria in any fever after travel to a malaria area in the past year (especially sub-Saharan Africa - Plasmodium falciparum). It usually presents within 3 months; people visiting friends and relatives are at highest risk.
• Tests:
  • Thick and thin blood films (and rapid antigen test) - urgently.
  • Repeat 3 times over 72 hours if negative and malaria is still suspected.
  • Thin film gives the parasite percentage and species.
• Severe falciparum malaria - any of:
  • Parasitaemia over 2% (over 10% is very severe).
  • Impaired consciousness or seizures (cerebral malaria).
  • Severe anaemia (Hb under 80 g/L).
  • Hypoglycaemia.
  • AKI.
  • Acidosis (high lactate).
  • Pulmonary oedema or ARDS.
  • Shock.
  • Spontaneous bleeding or DIC.
  • Haemoglobinuria.
• Treatment (UK malaria guidelines):
  • IV artesunate 2.4 mg/kg at 0, 12 and 24 hours, then daily - then a full oral course (e.g. artemether–lumefantrine) once improving.
  • Quinine only if artesunate isn't available.
  • ICU; check glucose often (hypoglycaemia, especially with quinine); careful fluids (pulmonary oedema risk).
  • Monitor for delayed haemolysis 1–3 weeks after artesunate.
  • Discuss with infectious diseases.
• Uncomplicated falciparum malaria - oral artemether–lumefantrine (or atovaquone–proguanil). Admit, because patients can deteriorate quickly.
• Non-falciparum malaria (vivax, ovale) - chloroquine or ACT, then primaquine or tafenoquine to clear liver stages (check G6PD first).

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Methaemoglobinaemia

• What it is: Iron in haemoglobin is oxidised to the ferric form, which can't carry oxygen.
• Causes:
  • Drugs - dapsone, local anaesthetics (benzocaine, prilocaine), nitrates and nitrites (including recreational "poppers"), primaquine, rasburicase, sulfonamides.
  • Inherited enzyme deficiency (rare).
• Clues:
  • Cyanosis and breathlessness that don't improve with oxygen.
  • Pulse oximetry about 85% regardless of the actual oxygen level ("saturation gap") while the arterial pO2 is normal.
  • "Chocolate-brown" blood.
  • Headache, confusion, seizures, arrhythmias at high levels.
• Diagnosis: Co-oximetry on a blood gas (methaemoglobin level).
• Treatment:
  • Stop the cause; high-flow oxygen.
  • IV methylthioninium chloride (methylene blue) 1–2 mg/kg if the level is over about 20–30% or the patient has symptoms.
  • Avoid methylene blue in G6PD deficiency (it causes haemolysis and doesn't work) - use exchange transfusion or ascorbic acid instead.

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Hyperviscosity Syndrome

• Causes:
  • Paraproteins - IgM (Waldenström), IgA or IgG3 myeloma.
  • Leukostasis (acute leukaemia).
  • Very high haematocrit (polycythaemia).
• Features:
  • Visual disturbance - retinal vein engorgement ("sausage" veins), haemorrhages, papilloedema.
  • Neurological - headache, dizziness, confusion, drowsiness, stroke.
  • Mucosal bleeding - nosebleeds, gum bleeding.
  • Heart failure.
• Treatment:
  • Plasma exchange for paraproteins - rapid relief.
  • Leukapheresis and cytoreduction for leukostasis.
  • Venesection (with fluid replacement) for very high haematocrit.
  • IV fluids.
  • Avoid red cell transfusion until viscosity is reduced.
  • Avoid diuretics.
  • Then treat the underlying disease.

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HIT and Catastrophic Thrombosis

• Heparin-induced thrombocytopenia with thrombosis (see the Bleeding and Thrombosis chapter):
  • Platelets fall over 50% 5–10 days after heparin, with new clots.
  • Stop all heparin; start argatroban (or danaparoid, fondaparinux, a DOAC).
  • No platelets; no warfarin until platelets recover.
• Catastrophic antiphospholipid syndrome:
  • Rapid clotting in many organs over days.
  • Anticoagulation (heparin), high-dose steroids, plasma exchange and/or IVIg; ICU.
• Purpura fulminans - rapidly spreading skin necrosis with DIC, usually from meningococcal sepsis (or protein C deficiency). Antibiotics, protein C concentrate, blood products.
• VITT (vaccine-induced immune thrombocytopenia and thrombosis) - cerebral venous or splanchnic thrombosis with low platelets after adenoviral vector vaccines. IVIg, non-heparin anticoagulation.
• Massive PE - see the Respiratory Emergencies chapter.

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Overwhelming Post-splenectomy Infection

• Who: People without a working spleen - after splenectomy, sickle cell disease, coeliac disease, after splenic irradiation.
• Organisms: Pneumococcus (most), meningococcus, Haemophilus influenzae, Capnocytophaga (dog bites), malaria and babesiosis.
• Features:
  • Can go from a flu-like illness to septic shock, DIC and purpura fulminans within hours.
  • Mortality up to 50%.
• Action:
  • Immediate IV antibiotics (e.g. ceftriaxone) - don't wait for tests.
  • Sepsis bundle; ICU.
  • Patients should start their standby antibiotics at home at the first sign of fever and seek help.
• Prevention: Vaccines, penicillin prophylaxis, alert cards (see the Red Cells chapter).

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Severe Transfusion Reactions

• Any severe reaction:
  • Stop the transfusion; keep the IV line open with saline.
  • ABC assessment; call for help.
  • Check patient ID against the bag.
• Acute haemolytic (ABO incompatibility) - fever, loin pain, hypotension, haemoglobinuria, DIC:
  • Fluids to keep urine output up.
  • Return the bag; DAT, haemolysis screen, clotting.
  • Inform the lab immediately - another patient may have received the wrong blood too.
• Anaphylaxis - IM adrenaline 500 micrograms; airway; fluids.
• TACO - sit up, oxygen, furosemide.
• TRALI - oxygen, ventilatory support; no diuretics.
• Bacterial contamination - cultures from the patient and the bag; broad-spectrum antibiotics.
• Report to SHOT and SABRE.
• See the Haemoglobinopathies and Transfusion chapter for the full table.

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Drug Reference Table

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Spot the Emergency

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Exam-style Scenarios

1. A 35-year-old woman has confusion, petechiae and dark urine. Hb 78, platelets 9, schistocytes on film, creatinine 130, clotting normal.
Answer: TTP until proven otherwise.

• Send ADAMTS13 before treatment; urgent transfer to a TTP centre.
• Same-day plasma exchange; IV methylprednisolone; caplacizumab; rituximab.
• No platelet transfusion.

2. A man is brought in after a motorbike crash with a BP of 75/40 and an expanding thigh haematoma.
Answer: Major haemorrhage.

• Activate the major haemorrhage protocol; TXA 1 g IV (within 3 hours of injury).
• Emergency O blood, then red cells and FFP about 1:1; cryoprecipitate if fibrinogen under 1.5.
• Keep him warm; check calcium; permissive hypotension until surgical control.

3. A 50-year-old returned from Ghana 8 days ago with fever and drowsiness. The thin film shows 8% P. falciparum.
Answer: Severe falciparum malaria.

• IV artesunate; ICU review.
• Check glucose frequently, lactate, kidney function; careful fluids.
• Switch to a full oral course when improving; watch for delayed haemolysis.

4. A woman on clozapine has a sore throat and a temperature of 38.6 °C. Neutrophils are 0.1 × 10⁹/L.
Answer: Clozapine-induced agranulocytosis with neutropenic sepsis.

• Stop clozapine permanently; inform the clozapine monitoring service and psychiatry.
• IV piperacillin–tazobactam within 1 hour; consider G-CSF.

5. A man with AML has a WCC of 180 × 10⁹/L, is breathless and confused, and his Hb is 70 g/L.
Answer: Leukostasis.

• IV fluids; urgent cytoreduction (hydroxycarbamide or chemotherapy); consider leukapheresis.
• Avoid red cell transfusion if possible; keep platelets above 30–50.
• TLS prevention with rasburicase; confirm oxygenation by pulse oximetry.

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Key Points

• Major haemorrhage: one call to activate the protocol; TXA in trauma and obstetrics; balanced products; avoid excess crystalloid; keep warm; check calcium.
• Targets in bleeding: Hb 70–90, platelets over 50 (over 100 in head injury), fibrinogen over 1.5 (over 2 in obstetrics).
• Warfarin bleed: PCC plus IV vitamin K. Dabigatran: idarucizumab. Xa inhibitors: PCC, or andexanet for GI bleeds.
• DIC: treat the cause; replace products only if bleeding or before procedures.
• Schistocytes with low platelets: TTP until proven otherwise - plasma exchange the same day; no platelets.
• STEC-HUS: supportive care; avoid antibiotics and antimotility drugs. Atypical HUS: eculizumab.
• Suspected APL: start ATRA immediately and replace fibrinogen.
• Leukostasis: cytoreduce, hydrate, avoid red cell transfusion; beware pseudohypoxia and pseudohyperkalaemia.
• Sore throat or fever on carbimazole, clozapine or sulfasalazine needs an urgent FBC.
• HLH: fever, cytopenias, splenomegaly and very high ferritin - treat urgently.
• Fever after travel: urgent malaria films; severe falciparum needs IV artesunate.
• Methaemoglobinaemia: SpO2 about 85% with normal pO2 - methylene blue (not in G6PD deficiency).
• Hyperviscosity: plasma exchange; avoid transfusion.
• Fever in an asplenic patient: IV antibiotics immediately.