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Peripheral Blood Smear

For normal reference ranges of different cell types in adults, see Leucocytosis.

Blood smear denotes microscopic examination of the peripheral blood, performed by a physician on a peripheral blood film stained with the May-Grünwald-Giemsa method.
- Blood cell morphology
- Differential white cell count is performed with an automated blood cell counter and only abnormal samples ("flagged", about 10-20%) are checked microscopically by a laboratory technician. Depending on the skills of the technician and the local practices, she/he may give comments that provide information partly similar to the morphological examination proper.

Blood morphology examination is indicated when a laboratory physician's interpretation is needed regarding the morphology of peripheral blood cells, for example:
- when suspecting fragmentation haemolysis
- when suspecting so-called pseudothrombocytopenia, thrombocytopathy or thrombotic microangiopathy in a patient with thrombocytopenia
- in the differential diagnosis of macrocytic anaemia
- when suspecting a hereditary abnormality of erythrocytes (if thalassaemia Thalassaemias or haemoglobinopathy is suspected, the primary examination, in addition to the numeric blood picture, is an analysis of haemoglobin fractions).
Before requesting a peripheral blood smear test, a complete blood count and, in a patient with anaemia, reticulocyte count should be examined.
Morphological examination of a bone marrow aspiration sample also includes examination of peripheral blood smear.
Differential white cell count and blood morphology are not suited for follow-up; WBC or a more specific parameter (for example reticulocytes in haemolysis) is preferred.
Table T1 lists some diseases in which blood haemoglobin concentration and both leucocyte count and thrombocyte count may be normal and blood morphology may lead to the correct diagnosis. In some of these, examination of the complete blood count provides valuable additional information and may render the peripheral blood smear unnecessary.

Condition	Findings in morphological blood analysis
Compensated haemolysis Haemolytic Anaemia	Spherocytosis, polychromasia, red cell agglutination
Hereditary spherocytosis	Spherocytes, polychromasia
Hereditary elliptocytosis	Elliptocytes (ovalocytes)
Myelofibrosis Myelofibrosis (Mf)	Teardrop poikilocytes, leucoerythroblastic picture
Bone marrow infiltrates (myelofibrosis)	Teardrop poikilocytes, leucoerythroblastic picture
Asplenia (after splenectomy, spleen infiltrates, atrophy)	Howell-Jolly bodies, acanthocytes, target cells
Thalassaemia Thalassaemias	Hypochromasia, target cells
Lead poisoning	Punctate basophilia
Early megaloblastic anaemia or deficiency of folate Megaloblastic Anaemia	Hypersegmentated neutrophils
DIC	Fragmented red cells (schistocytes)
Mechanical haemolysis	Fragmented red cells
Severe infections Sepsis	Neutrophilia, coarse granulation of neutrophils
Infectious mononucleosis Mononucleosis	Transformed (reactive) lymphocytes
Hereditary anomalies involving leucocytes and platelets	Specific morphological changes in affected cells (e.g. giant platelets in Bernard-Soulier syndrome)
Agranulocytosis Leucopenia	Deep neutropenia
Allergic conditions	Eosinophilia
Chronic lymphocytic leukaemia Chronic Lymphocytic Leukaemia (CLL)	Relative lymphocytosis, smashed lymphocytes
Acute leukaemia (in the early stage) Acute Leukaemias in Adults	Blasts