Anaemia

Introduction

Anaemia is a condition in which the absolute number of red cells in the circulation is abnormally low. The diagnosis is usually made on the basis of the full blood count (FBC). This, together with the blood film, offers qualitative as well as quantitative data on the blood components; a set of normal values is shown in Box 13.1.1 .

The average life span of a normal red blood cell in the circulation is from 100 to 120 days. Aged red cells are removed by the reticuloendothelial system but, under normal conditions, are replaced by the marrow, such that a dynamic equilibrium is maintained. Anaemia develops when red cell loss exceeds red cell production. It follows that the anaemic patient is doing at least one of three things: not producing enough red cells, destroying them too quickly or bleeding.

The overriding functional importance of the red cell resides in its ability to transport oxygen, bound to the haemoglobin (Hb) molecule, from the lungs to the tissues. Functionally, anaemia may be regarded as an impairment in the supply of oxygen to the tissues, and the adverse effects of anaemia, from whatever cause, are a consequence of the resultant tissue hypoxia.

Anaemia is not a diagnosis: rather, it is a clinical or a laboratory finding that should prompt a search for an underlying cause ( Box 13.1.2 ).

Anaemia Secondary To Haemorrhage

Clinical features

Although it may be obvious on history and examination that a patient is bleeding, occasionally the source of blood loss is occult and the extent of the loss underestimated.

In the context of trauma, the history often gives clear pointers to both the sites and extent of blood loss. Consideration of the mechanism of injury may allow anticipation of occult pelvic, intraperitoneal or retroperitoneal bleeding. Intracranial bleeding is never an explanation for hypovolaemic shock in an adult.

In the absence of trauma, it is essential to obtain an obstetric and gynaecological history especially in women of childbearing age. The past medical history may point to a known haematological abnormality or a chronic disease process. A drug history is always relevant, as many drugs cause marrow suppression, haemolytic anaemia and bleeding. The family history may point to hereditary disease, and the social history may alert the clinician to an unusual occupational exposure in the patient’s past or to recreational activities liable to exacerbate an ongoing disease process. The systems review is particularly relevant to the consultation with middle-aged or elderly male patients, who must be asked about symptoms of altered bowel habit and weight loss.

The symptomatology of anaemia proceeds from vague complaints of tiredness, lethargy and impaired performance through to more sharply defined entities such as shortness of breath on exertion, giddiness, restlessness, apprehension, confusion and collapse. Co-morbid conditions may be exacerbated (the dyspnoea of chronic obstructive airway disease) and occult pathologies unmasked (exertional angina in ischaemic heart disease).

Anaemia of insidious onset is generally better tolerated than that of rapid onset because of cardiovascular and other compensatory mechanisms. Acute loss of 40% of the blood volume may result in collapse, whereas—in some developing countries—it is not rare for patients with Hb concentrations only 10% of normal to be ambulant. Trauma superimposed on an already established anaemia can lead to rapid decompensation.

The cardinal sign of anaemia is pallor. This can be seen in the skin, lips, mucous membranes and conjunctival reflections. Yet not all anaemic patients are pallid and not all patients with a pale complexion are anaemic. Patients who have suffered an acute haemorrhage may show evidence of hypovolaemia: tachycardia, hypotension, cold peripheries and sluggish capillary refill. The detection of postural hypotension is an important pointer toward occult blood loss. Conversely, patients with anaemia of insidious onset are not hypovolaemic and may manifest high-output cardiac failure as a physiological response to hypoxia.

Other features of the physical examination may provide clues to the aetiology of anaemia. The glossitis, angular stomatitis, koilonychia and oesophageal web of iron deficiency anaemia are uncommon findings. Bone tenderness, lymphadenopathy, hepatomegaly and splenomegaly may point to an underlying haematological abnormality. The rectal and gynaecological examinations can sometimes be diagnostic.