AS Adewoyin1 and B. Nwogoh2
- Dept. of Haematology & Blood Transfusion, University of Benin Teaching Hospital, Benin City, Edo State.
- Dept. of Haematology & Blood Transfusion, University of Calabar Teaching Hospital, Calabar, Cross River State.
The peripheral blood film (PBF) is a laboratory work-up that involves cytology of peripheral blood cells smeared on a slide. As basic as it is, PBF is invaluable in the characterization of various clinical diseases. This article highlights the basic science and art behind the PBF. It expounds its laboratory applications, clinical indications and interpretations in the light of various clinical diseases. Despite advances in haematology automation and application of molecular techniques, the PBF has remained a very important diagnostic test to the haematologist. A good quality smear, thorough examination and proper interpretation in line with patient’s clinical state should be ensured by the haemato-pathologist. Clinicians should be abreast with its clinical utility and proper application of the reports in the management of patients.
Keywords: Peripheral blood smear, Preparation, Examination, Interpretation, Reporting, Blood cells morphology.
Dr. A.S. Adewoyin
Dept. of Haematology and Blood Transfusion,
University of Benin Teaching Hospital,
Benin City, Edo State
In patient care, diagnostic formulations rest on a tripod consisting of clinical history, physical examination and laboratory investigations. The Literature reveals that as much as 70% of clinical decisions and diagnoses are supported by laboratory medicine.1 Peripheral blood film (PBF) is a basic and a highly informative haematological tool at the clinician’s disposal in screening, diagnosis and monitoring of disease progression and therapeutic response. An adept understanding of peripheral blood interpretation is important for a successful clinical practice.
The diagnostic relevance of a PBF is enormous. The PBF exposes the morphology of peripheral blood cells, which ensures its place in the morphologic diagnosis of various primary and secondary blood and blood related diseases. It’s diagnostic relevance has not been lessened by advances in haematology automation and molecular techniques.
This article attempts to summarize the preparation and reporting of peripheral blood film, its clinical interpretations and the common peripheral blood diagnosis. This will enhance the understanding of PBF interpretations by Clinicians.
INDICATIONS FOR A PERIPHERAL BLOOD FILM
Initiation of a PBF is often a clinical request by the attending clinician on account of a clinical suspicion or less frequently initiated by the laboratory.2, 3 The laboratory may initiate peripheral blood film based on abnormal findings from an automated count or patients clinical information whose diagnosis may be supported by a peripheral blood film. The latter is guided by individual laboratory policies or local regulating guidelines.2
Common clinical indications for peripheral blood film analysis include unexplained cytopenia: anaemia, leucopenia or thrombocytopenia; unexplained leukocytosis, lymphocytosis or monocytosis; unexplained jaundice or haemolysis; features of congenital haemolytic anaemias such as splenomegaly, jaundice or bone pains; suspected chronic or acute myeloproliferative disease e.g. chronic myeloid leukaemia; suspected organ failure such as renal disease, liver failure; features of hyperviscosity syndrome as in paraproteinaemias, leukaemic hyperleucocytosis, polycythaemia; severe bacterial sepsis and parasitic infections; malignancies with possible bone marrow involvement; suspected cases of nutritional anaemia; suspected chronic lymphoproliferative diseases such as chronic lymphocytic leukaemia; lymphoma with leukaemic spills; evaluation of therapeutic response in haemopathies among others.2, 4, 5
PREPARATION OF A PERIPHERAL BLOOD FILM SLIDE
To ensure accurate and reliable results, pre-analytical variables that can affect the quality of film must be controlled. These include patient preparation and consent, blood sampling technique, transport to the laboratory and sample preservation. Blood sampling is invasive therefore the patient/client should be counselled on the procedure. Commonly, blood is obtained from peripheral veins and stored in anticoagulant bottle. Blood to anticoagulant ratio should be in the right proportion. Rarely, capillary blood may be obtained by finger-prick. Care should be taken to ensure minimal tissue damage. Excess tissue fluid affects the distribution of the cellular elements of blood. Ethylene diamine tetra-acetic Acid (EDTA) is the anticoagulant of choice. Samples should be sent to the laboratory as soon as possible. Samples are best analyzed within 2 hours of blood collection. Delay in preparation of blood smear may allow for the degeneration of the cellular elements of blood and may result in a pseudo-thrombocytopenia (falsely reduced platelet count) due to formation of platelet aggregates.2
Slide preparation is done by trained personnel preferably a medical laboratory technologist, who can ensure quality slides for microscopy. Laboratory assistants can also be trained in the art of slide preparation.