Leukocyte Morphology – Definition & Diagnosis
Leukocyte morphology refers to the microscopic evaluation of white blood cells. It is a key diagnostic tool in haematology for detecting blood disorders and infections.
Things worth knowing about "Leukocyte morphology"
Leukocyte morphology refers to the microscopic evaluation of white blood cells. It is a key diagnostic tool in haematology for detecting blood disorders and infections.
What is Leukocyte Morphology?
Leukocyte morphology is the microscopic examination and assessment of white blood cells (leukocytes) based on their shape, size, internal structure, and degree of maturity. It is a fundamental component of clinical haematology and provides critical diagnostic information regarding blood disorders, immune system conditions, infections, and inflammatory processes.
As part of a differential blood count, the various types of leukocytes are classified and assessed for pathological changes. The evaluation is performed on a specially stained peripheral blood smear examined under a light microscope.
Types of Leukocytes and Their Morphological Features
There are five main types of leukocytes, each with distinct morphological characteristics:
- Neutrophils: The most abundant white blood cells. They have a multi-lobed nucleus and fine, pale pink granules in the cytoplasm. They are the primary defence against bacterial infections.
- Eosinophils: Identified by their bright red-orange granules and bilobed nucleus. Elevated counts are associated with allergic conditions and parasitic infections.
- Basophils: The rarest granulocytes, characterised by large dark-blue granules that may obscure the nucleus. They are involved in allergic reactions and inflammatory processes.
- Monocytes: Large cells with a kidney-shaped or horseshoe-shaped nucleus and grey, vacuolated cytoplasm. They are key players in immune defence and differentiate into macrophages in tissue.
- Lymphocytes: Small to medium-sized cells with a round, dense nucleus and a narrow rim of cytoplasm. They are central to adaptive immunity, comprising B cells and T cells.
How the Examination is Performed
A peripheral blood smear is prepared on a glass slide and stained using a specialised technique, most commonly the May-Gruenwald-Giemsa stain or the Wright stain. The stained preparation is then evaluated by an experienced haematologist or by an automated haematology analyser.
Manual review by a specialist remains indispensable, especially when haematological malignancy is suspected, as automated systems may not reliably detect all pathological cell forms.
Pathological Findings and Their Clinical Significance
Deviations from normal leukocyte morphology can indicate a wide range of conditions:
- Left shift: Increased presence of immature granulocytes (band neutrophils, metamyelocytes) in the peripheral blood, typically seen in severe bacterial infections or sepsis.
- Toxic changes: Toxic granulations, Doehle bodies, and vacuolisation of neutrophils in response to severe infections.
- Blasts: Immature precursor cells circulating in the blood, indicating acute leukaemia.
- Atypical lymphocytes: Enlarged, activated lymphocytes seen in viral infections such as Epstein-Barr virus (infectious mononucleosis).
- Hypersegmented neutrophils: Neutrophils with five or more nuclear lobes, characteristic of vitamin B12 or folate deficiency.
- Pelger-Huet anomaly: Neutrophils with a bilobed or rod-shaped nucleus, occurring as a congenital trait or as an acquired finding in myelodysplastic syndromes.
Clinical Relevance
Leukocyte morphology is an essential part of haematological diagnostics. It complements quantitative blood count parameters and enables a targeted assessment of the underlying disease process. Indications for morphological evaluation include:
- Suspected leukaemia or lymphatic disease
- Unexplained leukocytosis or leukopenia
- Severe infections and sepsis
- Fever of unknown origin
- Follow-up examinations in known haematological disorders
References
- Bain, B.J. - Blood Cells: A Practical Guide. 5th edition, Wiley-Blackwell, 2015.
- Hoffbrand, A.V. & Moss, P.A.H. - Hoffbrand's Essential Haematology. 7th edition, Wiley-Blackwell, 2016.
- World Health Organization (WHO) - WHO Classification of Tumours of Haematopoietic and Lymphoid Tissues. 4th edition, IARC Press, 2017.
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