Haemolytic anaemia

Haemolytic anaemia keeps appearing randomly throughout the CICM Paert II exam, where it pops up in a different form every time. Autoimmune haemolysis had been the subject of Question 11.2 and Question 11.3 from the first paper of 2012. Also, Question 7.1 from the first paper of 2016 presented a case of warm haemolysis with spherocytosis. Plus, in Question 26 from the second paper of 2021, G6PD appeared as a main cause of haemolysis and anaemia, and the trainees had to reconstruct the haemolytic picture on the basis of methaemoglobinaemia and a raised carboxyhaemoglobin. For completely arbitrary and probably entirely lazy reasons, G6PD has ended up getting the back end of this haemolysis page, instead of its own page. 

Clinical and laboratory features of autoimmune haemolysis

The distinction here is autoimmune destruction of RBCs, as opposed to some other (usually mechanical) process.  Some of the historical features suggestive of mechanical or extravascular haemolysis are listed below:

• Recent fevers, recent travel (haemolysis is due to a viral haemorrhagic fever or malaria)
• Recent septic shock (haemolysis is the consequence of DIC)
• Valve pathology or valve replacement i.e. the cells were broken by shear stress in a mechanical aortic valve
• Exposure to extracorporeal circuit  i.e. the cells were shredded by the centrifugal pump of ECMO.
• Splenomegaly: a cause of extravascular haemolysis
• Features of arterial insufficiency, including leg ulcers (eg. in sickle cell anaemia)

Features of history associated with autoimmune haemolysis

• Recent blood transfusion (haemolysis is due to a transfusion reaction)
• Recent fevers, recent travel (haemolysis is due to a viral haemorrhagic fever or malaria)
• Recent septic shock (haemolysis is the consequence of DIC)
• Recent commencement of a new medication (drug-inducd haemolysis is caused by 5-FU, methyldopa, quinine, diclofenac, penicillin, cephalosporins, and many others).
• History of pigmented galstones: suggests chronic haemolysis
• History of recent infection:  many of the causes listed in the table below are post-infectious
• History of "stress", eg. for patients with G6PD (this could be surgery, infection, or exposure to an oxidant. Classically, fava beans are mentioned.
• Weight loss, night sweats, and other features suspicious of haematological malignancy
• Arthralgia is mentioned in Question 7.1 from the first paper of 2016, and may represent an autoimmune disease such as SLE, or an infective process such as Bartonella.

Features of physical examination

• Jaundice is mandatory: bilirubin is raised.
• Dark urine suggests conjugated bilirubin is present in excess; whereas jaundice in the absence of pigmented urine suggests that the bulk of the bilirubin is unconjugated. Theoretically, haemolysis should give rise to a predominantly unconjugated hyperbilirubinaemia, but provided you have a healthy liver this is almost never seen. Usually some fraction of conjugated bilirubin is present, and ends up appearing in the urine. 

Laboratory features common to all haemolytic anaemias

• Morphologic RBC abnormalities: such as spherocytosis or fragmented RBCs, as well as pathognomonic erythrocytes such as sickle cells.
• High reticulocyte count: because a normal bone marrow responds to anaemia by ramping up the production of RBCs.
• High LDH:  lactate dehydrogenase is an enzyme which leaks out of pretty much any damaged cells, and so is not specific for haemolysis. However, nor is bilirubin. Regardless, the college will expect you to mention both in an exam answer.
• Haptoglobin: the protein responsible for iron transport will usually be low when there is too much iron to transport. It is also an acute phase reactant, which means it does not necessarily have to be low in the presence of haemolysis.
• Free haemoglobin will be elevated as it spills out of RBCs. There may even be haemoglobinuria.

Laboratory features specific to autoimmune causes of haemolytic anaemia

• DAT, direct antiglobulin test or direct Coombs Test, demonstrates that the RBCs are coated with antibody and/or complement. Question 7.1 from the first paper of 2016 offers us a DAT which is positive for IgG as well as C3d, unequivocally identifying an autoimmune cause for the haemolysis. An excelent resource which explains DAT is an article by Zantek et al (2012).
• DAT helps discriminate between a  "warm" and a "cold" haemolytic anaemia.
• When haemolysis is "warm", the autoimmune haemolytic anaemia is caused by antibodies maximally active at human body temperature, and this is usually caused by IgG. The DAT comes back positive for both IgG and C3d, the latter being a complement product
• Hamolysis caused by IgM usually occurs in cold conditions, and the DAT comes back positive for C3d but not IgG.

Causes of autoimmune haemolytic anaemia

So, you're haemolysing. Why are you doing that? A good overview of this topic can be found in the American Journal of Haematology. Their breakdown of the classifications of haemolytic anaemia looks a little like the table offered below. Generally, people tend to classify them according to the effects of teperature on antibody reactivity.

Differential Causes of Autoimmune Haemolytic Anaemia

Warm haemolytic anaemia	Cold haemolytic anaemia
Idiopathic primary haemolytic anaemia Viral infections, including HIV Drugs, eg. penicillin, methyldopa, 5-FU, diclofenac, etc... Lymhoproliferative disorders: CLL Lymphoma Multiple myeloma Hodgkins lymphoma Waldenstrom's macroglobulinaemia Autoimmune disorders, particularly SLE and rheumatoid arthritis	Post-infectious colad agglutinin disease Syphilis Post-viral Mycoplasma pneumoniae EBV, VZV, CMV, HIV Adenovirus Influenza viruses Paroxysmal cold haemoglobinuria Idiopathic Virus-associated (EBV, CMV, etc)

Management of autoimmune haemolysis

"How I treat autoimmune hemolytic anemias in adults" by Lechner and Jäger, who presumably treat it in the same way. In brief, warm haemolysis benefits from steroids and splenectomy, whereas cold haemolysis does not.

Generic management of autoimmune haemolysis

• Plasmapheresis is only indicated in fulminant acute haemolysis. Only a temporary improvement is to be expected, as this treatment does nothing to treat the underlying autoantibody production.
• Rituximab, a CD20 monoclonal antibody, has been effective in cases of cold haemolytic anaemia where a B-cell dominant lymphoproliferative disorder is at fault. It seems to be more effective in warm haemolysis.
• Eculizumab, a terminal complement inhibitor (monoclonal C5 antibody) has been found effective in various case reports (eg. Kim et al, 2016), even though it is indicated only for atypical HUS and paroxysmal nocturnal haemolobinuria.

Specific management of warm haemolysis

• Corticosteroids appear to be effective as the first-line treatment. Among other thngs, the steroids reduce the synthesis of autoantibodies by B-cells.
• Splenectomy is the second-line treatment. The spleen's macrophages are responsible for removing IgG-coated RBCs; also the spleen is a site of antibody production.
• Cyclophosphamide / azathioprine  are reserved for those who fail steroids and splenctomy (or cannot have a splenectomy).
• IV immunoglobulin is not strongly indicated: some reports show benefit, others don't.
• Danazol, a synthetic steroid derivative of ethisterone, is very old school (Pignon et al, 1993) - it is mentioned in the college answer to Question 7.1 from the first paper of 2016. It is usually used for endometriosis.

Specific management of cold haemolysis

• Avoid cold exposure! Without cold, there is no haemolysis.
• Forget corticosteroids.They are rarely useful.
• Forget splenectomy. It has no positive effect.

Glucose-6-phosphate Dehydrogenase (G6PD) deficiency

The CICM candidates, reading though this compendium of footnotes to past CICM exam questions, would naturally come to the conclusion that the only things they need to know about this condition is that it can produce Heinz bodies (Question 24.3 from the second paper of 2010), and that methylene blue is contraindicated in this condition (Question 10.2 from the second paper of 2020). That impression would have been accurate for the first twenty or so years of the written exam, until G6PD deficiency became the Question 26 from the second paper of 2021. To score marks here, the candidates would have had to:

• Recognise the ethnic groups at greatest risk of having G6PD (i.e. mainly those from malaria-prevalent countries)
• Recognise haemolysis from incomplete blood result data (mainly blood film data suggesting red cell damage and a rapidly progressing anaemia)
• Recognise methaemoglobinaemia as one of the possible consequences of G6PD deficiency
• Quickly produce a list of correct investigations to confirm the diagnosis of G6PD deficiency

The likelihood of G6PD appearing again in the exam is small, as it seems to return only once in every twenty years, like some kind of comet. Still, in case this comes up again at some stage between now and 2041, it seems reasonable to at least cover the abovementioned aspects of it, in some brief summarised way. In case anybody needs a free article to read about this condition, one can recommend Beutler (1994) or Frank (2005).

Thus:

Definition and pathophysiology of G6PD deficiency

• Glucose-6-phosphate dehydrogenase is an enzyme of the pentose pathway.
• Its main role in erythrocytes is to provide reductive potential in the form of NADPH. G6PD reduces NADP+ to NADPH while oxidizing glucose-6-phosphate.
• Erythrocytes then use the NADPH to repair oxidative damage: NADPH is oxidized by glutathione reductase to regenerates reduced glutathione that is oxidized in the repair of oxidative damage 
• (G6PD) deficiency is an x-linked recessive mutation of glucose 6-phosphate dehydrogenase
• Failure to produce enough NADPH in the context of oxidative stress has the tendency to deplete glutathione through its conversion to glutathione disulfide.
• With ongoing oxidative stress, the sulfhydryl groups of haemoglobin and various other proteins are oxidized to disulfides or sulfoxides. 
• These denatured products precipitate into Heinz bodies.
• This sort of molecular garbage damages red cell membranes and marks red cells to be destroyed by the reticuloendothelial system, hence the acute haemolytic reaction and jaundice.

Populations at risk of G6PD deficiency

• Africans
• African Americans
• Southeast Asians
• Mediterranean populations
• Indians
• Latin Americans

Triggers for haemolysis in G6PD deficiency

• Foods
  • Fava bean (Vicia faba)
  • Bitter melon
  • Blueberries
• Drugs and chemicals
  • Dapsone
  • Methylene blue
  • Hair dyes
  • Cotrimoxazole
  • Sulfamethoxazole
  • Nitrofurantoin
  • Fluoroquinolones
  • Rasburicase
  • Primaquine
• Infections (could be any sort)
• DKA

Diagnostic tests to confirm G6PD deficiency

• Rapid fluorescent spot test, qualitatively detecting the generation of NADPH from NADP (the test is positive if the blood spot fails to fluoresce under ultraviolet light)
• Quantitative spectrophotometric analysis of NADP-NADPH conversion, where a sample of the patient's red cells is added to a mixture of glucose-6-phosphate NADP, and then the fluorescence is measured
• Specific genetic testing then follows

Associated findings in G6PD deficiency-induced haemolysis

• Heinz bodies
• Howel-Jolly bodies
• Bite cells and helmet cells (damaged erythrocytes)
• Vigorous reticulocytosis (there's nothing wrong with the bone marrow)
• Polychromasia
• Carboxyhaemoglobin (from haem metabolism)
• Methaemoglobinaemia, due to the inability to convert it back into haemoglobin (i.e. insufficient substrate for NADPH haemoglobin reductase)

Management of G6PD deficiency-related haemolysis

• Removal of the trigger factor
• Supportive care
• Hydration, aiming to protect the renal tubules from the ATN-inducing effects of free haemoglobin
• Transfusion, to reintroduce some donor erythrocytes which have plenty of G6PD