Defining Anaemia

Anaemia is defined by the World Health Organisation as a haemoglobin of <13.0g/dL for men and <12.0g/dL for women. However, this definition was mainly put in place for epidemiological studies, and fails to take into account the normal variation in haemoglobin levels with age and laboratory instruments.

Anaemia is hence more prudently defined as a haemoglobin that falls below the reference range determined by the testing laboratory. This requires that haemoglobin measurements are taken from normal individuals to determine a reference range.

Classification of Anaemia

Anaemia is classified in two major ways: morphology and mechanism. The morphological classification is based on an understanding of erythropoiesis; however, where it falls short is in the differential for a normocytic, normochromic anaemia, which is myriad.

The mechanistic classification relies on the principle that red blood cells cannot just disappear – anaemia results from one of a few things: reduced production, increased loss, sequestration or dilution (remember, haemoglobin is measured as a concentration).

The flowcharts below show the approaches of both.

Classification of Anaemia by MCV.

Classification of Anaemia by Mechanism.