Blood Cell Morphology and Indices

Blood cell morphology and indices describe the appearance and measured characteristics of the formed elements of blood. The red cell indices, computed from the automated count, summarise the average size and haemoglobin content of red cells, while the microscopic review of a stained peripheral blood film characterises the shape, colour, and inclusions of red cells, white cells, and platelets. Together they refine the picture provided by the numerical blood count.

Definition

Blood cell morphology is the microscopic description of the size, shape, colour, and inclusions of blood cells on a stained peripheral film, while the red cell indices (mean corpuscular volume, mean corpuscular haemoglobin, and mean corpuscular haemoglobin concentration) are quantitative measures of average red cell size and haemoglobin content derived from the count.

Scope

The entry covers the red cell indices and what they summarise, the role of the stained blood film, and the standardisation of morphological nomenclature and grading. It is an educational reference on how cell appearance and indices are described in the laboratory and does not provide diagnostic cut-offs or management advice.

Core questions

• What do the red cell indices summarise about a red cell population?
• What does microscopic review of the blood film add beyond the numerical count?
• How are morphological features named and graded in a standardised way?
• How do indices and film findings complement one another?

Key concepts

• Mean corpuscular volume (MCV)
• Mean corpuscular haemoglobin (MCH) and concentration (MCHC)
• Red cell distribution width (RDW)
• Anisocytosis and poikilocytosis
• Stained peripheral blood film
• Standardised morphological nomenclature and grading

Mechanisms

The red cell indices are derived from the automated measurement of red cell number, size, and haemoglobin, summarising the average volume and haemoglobin content of the population and describing its size variability (Buttarello, 2008). The stained peripheral blood film, examined microscopically, characterises features that indices cannot capture, including abnormal red cell shapes, inclusions, and the appearance of white cells and platelets; the ICSH has published recommendations standardising the nomenclature and grading of these features so that reports are consistent between observers (Palmer, 2015). Interpretation of the film is grounded in systematic morphological description (Bain, 2017).

Clinical relevance

Morphological description and the red cell indices help the laboratory characterise anaemias and other disorders of the formed elements and direct further testing. The entry explains how these features are measured and described; it is educational and is not a basis for individual diagnostic or treatment decisions.

Evidence & guidelines

The standardisation of morphological nomenclature and grading is set out in ICSH recommendations (Palmer, 2015), while the derivation and performance of the indices on automated analysers are reviewed in the laboratory literature (Buttarello, 2008).

Seminal works

• palmer-2015
• buttarello-2008

Frequently asked questions

What are the red cell indices?

They are quantities derived from the automated count, principally mean corpuscular volume, mean corpuscular haemoglobin, and mean corpuscular haemoglobin concentration, that summarise the average size and haemoglobin content of red cells; red cell distribution width describes how variable the cell sizes are.

Why examine a blood film when indices are available from the analyser?

Indices give averages but cannot describe the shape, colour variation, or inclusions of individual cells; microscopic review of a stained film characterises these morphological features using standardised nomenclature, adding information the numerical indices cannot provide.