- Haemolysis is the destruction of red blood cells prior to the end of their normal 120-day lifespan. Haemolysis may occur intravascularly or extravascularly (e.g. in the spleen or liver).
- Concerns may be raised for the presence of haemolysis in patients with anaemia, reticulocytosis or jaundice.
- Haemolysis can be caused by a wide variety of immune and non-immune conditions.
- Thrombotic microangiopathies such as thrombotic thrombocytopaenic purpura (TTP), haemolytic-uraemic syndrome (HUS) and disseminated intravascular coagulation (DIC) are important causes of haemolysis and should not be missed. HELLP syndrome (haemolysis, elevated liver enzymes, low platelets) may occur in pregnant patients. Mechanical haemolysis may be caused by severe valvular leaks, mechanical valves and other cardiac prostheses, by dialysis or ECMO circuits, or by repetitive trauma (e.g. by prolonged marching).
- Autoimmune haemolytic anaemias may be either warm or cold. Their causes are wide ranging and include infections, autoimmune disorders, lymphoproliferative disorders and drugs. Alloimmune haemolysis may occur following mismatched blood transfusion, in newborns, or post stem cell transplantation. Certain drugs may also cause immune haemolysis.
- Severe infections, malaria, meningococcal and Clostridium infections can cause haemolysis. Certain heavy metals such as copper and lead are also implicated. The syndrome of hypersplenism is a common cause in patients with liver disease, CCF or certain other conditions.
- Inherited red blood cell disorders such as hereditary spherocytosis, sickle cell anaemia and thalassaemias are more rare. Glucose-6-phosphate dehydrogenase deficiency may cause oxidative haemolysis and is more common in males of African or Mediterranean descent.
Causes of Haemolysis
- Warm autoimmune haemolytic anaemia - idiopathic, lymphoproliferative disorders, infection, autoimmune disorders, methyldopa, penicillins, cephalosporins, rifampicin, quinine, paracetamol, ibuprofen
- Cold agglutinin haemolysis - idiopathic, mycoplasma pneumoniae, EBV, lymphoma, paroxysmal cold haemoglobinuria
- Alloimmune haemolysis - transfusion of mismatched red blood cells, haemolytic disease of the newborn, post stem cell transplant
- Drug-induced haemolysis
Red Cell Fragmentation
- Microangiopathic haemolytic anaemia - TTP, HUS, DIC, preeclampsia / HELLP, SLE, malignant hypertension, brown snake bite
- Mechanical haemolysis - valvular leaks, cardiac prostheses, renal replacement, ECMO, march haemoglobinuria
Inherited Intrinsic RBC Disorders
- Enzymopathies - G6PD deficiency, pyruvate kinase deficiency
- Membranopathies - hereditary spherocytosis
- Haemoglobinopathies - sickle cell disease, thalassaemias
- Infection - severe sepsis, malaria, babeosis, Clostridium toxin, Meningococcus
- Heavy metals - copper (Wilson’s disease), lead
- Paroxysmal nocturnal haemoglobinuria
- Patients with anaemia may present with fatigue, lightheadedness, dyspnoea, and in severe cases with anginal symptoms. In patients with haemolytic anaemia, jaundice is a common presenting complaint. Acute haemolysis may present as a febrile state with generalised pain affecting the abdomen, bones or joints.
- In identifying a potential cause of haemolysis it is important to ask about recent blood transfusions, recent travel (for malaria risk) and history of autoimmune disease. Carefully check that patient's medications for any drugs that may cause haemolysis. Also ask about a family history of haemoglobinopathy and solid organ or haematologic malignancy.
- On examination, check for jaundice by examining the skin and sclerae. Look for signs of anaemia such as tachycardia or pallor of the conjunctivae or hand creases. Examine for splenomegaly as an indicator of severe haemolysis or hypersplenism.
- Symptoms of anaemia - fatigue, lethargy, lightheadedness, shortness of breath, chest pain, headache
- Symptoms of acute haemolysis - fevers, abdominal pain, arthralgias, headache, malaise
- Recent blood transfusion
- Recent travel
- Past medical history - autoimmune disease, cardiac prosthesis
- Medication history
- Family history - thalassaemia, malignancy
- Signs of anaemia - conjunctival pallor, pale hand creases, tachycardia
Approach to Diagnosis
- Following haemolysis, haemoglobin is metabolised to haem and then bilirubin, which overwhelm's the liver's capacity to conjugate it. Elevated unconjugated bilirubin is an indicator of haemolysis though can be caused by other disorders including resorption of a large haematoma, certain medications, inherited disorders, acute hepatitis or cirrhosis. As such it is important to also look at the remainder of the liver function panel when interpreting the bilirubin.
- Haptoglobin binds plasma free haemoglobin following red cell lysis, and as such the haptoglobin level will be reduced in haemolysis. Haptoglobin may also be reduced in liver disease.
- Lactate dehydrogenase is a relatively non-specific marker of cell damage, though it should be tested as part of a haemolytic screen as its elevation will be a supporting feature.
- Elevated reticulocytes (non-nucleated immature red cells) are indicative of compensatory erythropoiesis due to haemolysis, though they may also be elevated following recovery from anaemia or in the context of increased red blood cell requirement.
- In order to identify intravascular haemolysis (as opposed to extravascular haemolysis, occurring mainly in the spleen or liver), several tests can be performed. Plasma free haemoglobin will be elevated in intravascular haemolysis, as will urine haemoglobin and urine haemosiderin.
Markers of Haemolysis
- Hyperbilirubinaemia (unconjugated)
- Reduced haptoglobin
- Elevated LDH
- Elevated reticulocytes
- Elevated plasma free haemoglobin
- Elevated urine haemoglobin - urine dipstick positive for blood but no RBC
- Elevated urine haemosiderin - brownish urine due to excess iron stored as haemosiderin
Identifying the Cause of Haemolysis
- In all patients, a full blood count should be performed to assess the severity of anaemia. Presence of thrombocytopaenia may be a marker of thrombotic microangiopathies such as DIC, TTP or HUS. Hypersplenism can also cause haemolysis and thrombocytopaenia.
- A blood film should also be performed. The presence of fragments (schistocytes) is suggestive of microangiopathic causes, though may also occur with mechanical haemolysis. Spherocytes may be a marker of immune haemolysis. Prekeratocytes, keratocytes and irregularly contracted cells are indicators of oxidative haemolysis such as due to G6PD deficiency or unstable haemoglobins. Sickle cells are pathognomonic of sickle cell disease, though are not always present.
- A direct antigen test (DAT, or Coomb's test) should alway be performed if there is concern for haemolysis. A positive test suggests an immune cause of haemolysis such as warm autoimmune haemolytic anaemia, cold agglutinin disease or transfusion mismatch.
- A coagulation profile should be performed; check whether the patient is on anticoagulation as this will affect the result. Disseminated intravascular coagulation (DIC) will cause a consumptive coagulopathy - if there is concern for DIC then the D-dimer and fibrogen levels should also be tested. Keep in mind that liver disease can also affect the coagulation profile.
- Test the patient's renal function, especially if there is concern for haemolytic uraemic syndrome.
- Certain other tests should also be considered in specific situations. If there is concern for sepsis then blood cultures and other relevant cultures should be performed. Thick and thin blood smears will test for malaria. ADAMTS13 is a metalloprotease that cleaves Von Willebrand factor; its level will be reduced in TTP. Haemoglobin electrophoresis can be used to diagnose haemoglobinopathies. Flow cytometry may be considered (for CD55/CD59) if there is concern for paroxysmal nocturnal haemoglobinuria.
Tests to Identify Cause
- FBC - type and severity of anaemia, thrombocytopaenia, WCC abnormalities
- Blood film - spherocytes, schistocytes, polychromasia
- Direct antigen test (for an immune cause of haemolysis)
- Coagulation profile
- UEC - renal function
Other Tests to Consider
- Bacterial cultures (sepsis)
- Thick & thin blood smears (malaria)
- Haemoglobin electrophoresis (haemoglobinopathies)
- Flow cytometry - for CD55/CD59 (PNH)
- ADAMTS13 (TTP)
- Thrombotic microangiopathies such as TTP, HUS and DIC are medical emergencies and must be diagnosed and treated expediently.
- If the patient has recently recieved a blood transfusion and the DAT is positive, contact the blood bank to compare blood types and check for antibodies.