Blood smear preparation

Introduction

• Blood smears are simple to perform and can provide useful information on all blood cell lines.
• Platelet counts, white blood cell differential counts and morphology, red blood cell morphology.
• Definitive diagnosis of blood parasites, eg Babesia canis.
• Characterization of hematological disorders which will assist in definitive diagnosis.

Uses

• Indicated in:
  • Suspected cases of anemia, thrombocytopenia or leukemia.
  • Suspected inflammatory disease (of infectious or immune-mediated origin).
  • As an adjunct to in-house hematology analyzers.

Advantages

• Very rapid simple technique requiring minimal equipment.
• Can be performed with very small volumes of blood.
• Accurate assessment of cell morphology which may be affected by storage or transport.

Disadvantages

• Must use clean slides to avoid holes appearing in the smear (grease spots).
• Smear must be rapidly air dried to ensure that cell morphology is preserved.

Preparation

• 5 min for preparation of patient and collection of blood sample.

Requirements

Materials required

Minimum equipment

• Microscope with oil-immersion lens for smear examination.

Minimum consumables

• 2 ml syringe and sterile needle.
• Clean glass slides (minimum 2).
• Capillary tube.
• Diff-Quik stain.

Ideal consumables

• Blood tubes containing EDTA anticoagulant.
• Glass slides with frosted end for labelling.
• Spreader slide.
• Leishman's stain for routine staining and special stains such as Giemsa for identification of reticulocytes, and some parasites, eg Babesia, Trypanosoma cruzi.

Sequelae

Reasons for treatment failure

• Collection of sample following multiple attempts at venepuncture may result in falsely depressed platelet counts due to platelet activation and clumping.
• Use of inappropriate anticoagulants or prolonged storage in some anticoagulants may affect cell morphology, eg EDTA can result in platelet clumping, smears should therefore be prepared as soon as possible after blood collection (always check the feathered edge for platelet clumps before performing a platelet count).
• Poor smear technique can result in altered cell morphology and make it difficult to perform cell counts.
• Always use an appropriate stain, eg Diff-Quik is adequate for platelet counts but will need to use Giemsa for reticulocyte counts.