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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 (MGG) method. The examination is useful in situations where a disease causes a specific change in the morphology of blood cells.
- Blood cell morphology examination is carried out by a laboratory physician.
- Differential white cell count is performed by an automated blood cell counter. The blood cell counter alerts the staff about abnormal white blood cells / cell counts. The abnormal samples are used for a MGG-stained smear, which is microscopically examined by a laboratory technician. The findings can be commented on according to local guidelines, providing 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
- hereditary red blood cell shape or membrane abnormality(e.g. spherocytosis http://www.orpha.net/en/disease/detail/822 or elliptocytosis http://www.orpha.net/en/disease/detail/288)
- thrombotic microangiopathy or hereditary macrothrombocytopathy in a patient with thrombocytopenia
- chronic lymphocytic leukaemia Chronic Lymphocytic Leukaemia (CLL) as a cause of lymphocytosis (in this case, a flow cytometric surface marker test should also be requested)
- blastema or lymphoma spillover into the peripheral blood Lymphomas in a situation where a bone marrow sample cannot be obtained (in this case a flow cytometric surface marker test should also be requested).
Before requesting a blood cell morphology test, a complete blood count, which includes also a differential white cell 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.
Blood morphology is not suited for follow-up; white blood cell count or a more specific parameter (for example reticulocytes in haemolysis) is preferred.

Suspected iron deficiency anaemia Iron Deficiency Anaemia
Suspected megaloblastic anaemia Megaloblastic Anaemia
Suspected hereditary haemoglobin abnormality, e.g. thalassaemia Thalassaemias, sickle cell anaemia Sickle Cell Disease or other haemoglobinopathies (in which case the primary investigation in addition to a numerical blood count is haemoglobin fractions)
High hemoglobin, erythrocytosis Erythrocytosis or thrombocytosis Thrombocytosis
Suspected immunologic thrombocytopenia (ITP)
Neutrophilia Leucocytosis or eosinophilia Eosinophilia
Isolated lymphopenia Leucocytosis
Investigation of an infection

Savolainen E-R, Tienhaara A. [Blood samples and morphological examinations]. In: Porkka K, Lassila R, Remes K, Savolainen E-R (eds.). [Diseases of the blood]. Duodecim Publishing Company Ltd 2015, p. 84-100.