Heinz Body Anaemia
| Summary | |
|---|---|
| Cause: | Oxidative injury to erythrocytes |
| Associated conditions: | Exposure to oxidative toxins |
| Differential diagnoses: | Other causes of anaemia |
| Diagnosis: | Examination of blood smears |
| Treatment: | Supportive |
Introduction
Heinz bodies are inclusion bodies that form within erythrocytes as a result of oxidative injury to the cell. Named after Robert Heinz, the German physician who first described them, they consist of precipitated haemoglobin and their presence can result in premature phagocytosis of erythrocytes [1]
Structure of haemoglobin
Haemoglobin is a conjugated protein consisting of four globin chains, each of which contains a heme group. Its structure allows it to combine reversibly with oxygen and is thus very important in the transportation of oxygen to tissues. Normally the iron within the heme group is in the ferrous (2+) form, the form able to combine with oxygen.
==Pathophysiology of oxidative damage to haemoglobin
Oxygen can produce reactive free radicals such as hydrogen peroxide. These substances are generated under normal physiologic conditions and there are enzyme mechanisms to prevent damage to the cell. When these mechanisms are overwhelmed, oxidative damage occurs. As erythrocytes have no organelles they are unable to synthesise proteins and so have limited ability to repair themselves.[1] The damaged cells have highly rigid membranes and so are more likely to be removed from circulation [2]
Oxidation results in three major changes to the haemoglobin molecules:
- Heinz bodies are produced when the sylfhydral groups in the globin part of the haemoglobin molecule undergoes oxidation, causing the molecule to become unstable. Heinz bodies are formed when the damaged haemoglobin molecules coalesce. [2] In most species, Heinz bodies can be removed from erythrocytes by the spleen.
- Methaemoglobinaemia formation occurs when the iron in the haemoglobin molecule is oxidised to the ferric (3+) state. In normal circumstances the methaemoglobin reductase enzyme reduces ferric (3+) back to ferrous (2+) but this system can become overwhelmed in some circumstances.[2] This is the only form of oxidative damage which is reversible.
- Eccentrocytes have their haemoglobin concentrated on one side of the cell, causing the opposite side of the cell to appear clear. They are probably formed
when there is damage to the erythrocyte membrane.
This article will cover only Heinz bodies in detail.
Substances causing Heinz body formation
Cats, dogs, horses and ruminants can all suffer from Heinz body anaemias but they are clinically significant mainly in the cat and dog.
Cats
Feline erythrocytes are particularly susceptible to oxidative damage as they have eight highly reactive sulfhydryl groups, as opposed to two less reactive ones in other species. In addition, the cat spleen is less efficient in the removal of Heinz bodies from erythrocytes. These two characteristics mean that cats may have 5-10% of erythrocytes containing Heinz bodies under normal circumstances and makes them very susceptible to developing clinical signs of toxicity on exposure to oxidative substances.
- Paracetamol (known as acetominophen in the US) - cats have a low level of N-acetyltransferase enzymes, which prevents them from metabolising the drug to non-toxic substances. They are also relatively deficient in methaemoglobin reductase and methaemoglobinaemia is also a feature of paracetamol toxicity in cats.
 |
This article is still under construction. |