Anaemia as a sign rather than a diagnosis
Anaemia is too little haemoglobin (the protein inside red blood cells that carries oxygen), a finding that points towards a disease rather than being one.
Remember
Anaemia, a low haemoglobin, is a sign rather than a diagnosis, so it should prompt a search for the cause, whether blood loss, poor production or excessive destruction of red cells.
Memory aid
anaemia is the smoke, and the job is to find the fire
Anaemia points towards a disease, so the task is to trace it to its cause.
Oxygen travels in the blood on haemoglobin, a protein inside the red blood cells. When the body has too little haemoglobin to meet its needs, the tissues receive too little oxygen. That shortage of haemoglobin is anaemia, and because the tissues then receive less oxygen, the typical symptoms are tiredness and breathlessness.
In practice, anaemia is defined by a measurement. In non-pregnant adults it is a haemoglobin below 130 g/L in males and below 120 g/L in females, although these limits can vary with factors such as ethnicity and other medical conditions. It is not defined by symptoms, and it is not tied to a single cause.
Anaemia is a sign rather than a diagnosis. A diagnosis names a disease, whereas a sign is a finding that points towards one. Anaemia can arise in many ways, and doctors group them into three: blood loss, poor production, or excessive destruction of red cells (haemolysis). The cause decides the treatment, so a low haemoglobin is where the investigation starts.
That is why even a mild or symptom-free anaemia is investigated. The aim is to find the primary problem so that it can be diagnosed and treated.
Key facts
- Definition
- too little haemoglobin to meet the body's needs, so the tissues receive too little oxygen.
- Males
- in non-pregnant adults, a haemoglobin below 130 g/L, although the limit can vary with factors such as ethnicity and other medical conditions.
- Females
- in non-pregnant adults, a haemoglobin below 120 g/L, although the limit can vary with factors such as ethnicity and other medical conditions.
- Mechanisms
- blood loss, poor production or excessive destruction of red cells.
- Meaning
- a sign of underlying pathology, not a standalone diagnosis.
- Action
- even mild or symptom-free anaemia is investigated so that the primary problem can be treated.
Exam traps
- A shortage of iron (iron deficiency) is the commonest cause of a low haemoglobin, but it does not define anaemia, because bleeding, haemolysis, kidney disease and inflammation also cause it.
- Anaemia is not a standalone diagnosis that explains symptoms such as fatigue, because it is a sign of an underlying problem, so the finding still has to be traced to its cause.
- An expanded plasma volume can dilute the haemoglobin, as in pregnancy, but that is not the usual basis of anaemia, because most anaemias are a true fall in the number of red cells from loss, poor production or destruction.
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