Finger-Prick Blood Samples

• Finger-Prick Blood Samples

  = Wet or Fresh Preparation

  • Microfilariae and Trypanomastigotes are large and motile in fresh blood preparations. Their presence can be easily detected.

  • Species identification is not possible.
• Finger-Prick Blood Samples

  = Capillary Tube Method

  • Collected using a heparinized capillary tube which is sealed at one end then centrifuge.

  • Four layers are formed from top to bottom: Fatty layer, Plasma, Buffy coat, Packed Red cells.

  • Microfilariae and trypanosomes are visualized at the buffy coat area under a microscope.
• Finger-Prick Blood Samples

  = Method

  + Buffy coat films

  • capillary tube is broken at the area of the white layer after centrifugation, buffy coat is then spread and stained with Giemsa or Wright stain,
• Finger-Prick Blood Samples

  = Method

  + Quantitative Buffy Coat (QBC)

  • Make use of a capillary tube pre-coated with acridine orange and potassium oxalate and a cylindrical float inserted to enlarge the layers of the buffy coat

  • After centrifugation, the tube is read using an ultraviolet microscope

  • The parasite’s DNA takes up the acridine orange stain causing florescence among the non-florescencing RBCs
• Finger-Prick Blood Samples

  = Method

  + Stained Smears

  • Consist of both thick and thin films; examination of blood films for parasites is always a STAT request.

  • Stained use for Blood Parasites
• Finger-Prick Blood Samples

  = Method

  + Giemsa Stain

  • Stain of choice because it provides optimal detail or intracellular malarial parasites.

  • Eosin: stains parasite chromatin and stippling shades of red or pink

  • Methylene blue = stains parasite cytoplasm blue.
• Finger-Prick Blood Samples

  = Method

  + Wright Stain

  • Already contains alcohol so fixation is not required before staining.

  = RBC: Light Red

  = Eosinophil granules: Bright red

  = WBC nuclei: Bright blue

  = Neutrophil granules: pink
• Finger-Prick Blood Samples

  = Method

  + Thick Films/Smears

  • Prepared from 2-3 drops of blood and spread over a 1-2 cm diameter area, allowed to dry and then dehemoglobinized.
  • If whole blood is used: Examiner should continue stirring about 30 seconds to prevent the formation of fibrin strands.
  • Must use clean, grease-free slides, air-dried at RT and never heat-fixed.
• Finger-Prick Blood Samples

  = Method

  + Thick Films/Smears

  • Stained WBCs serve as the quality control. Intact RBCs are seen at the very periphery of the film
  • Frequently satisfactory for screening purposes.
  • Higher concentration of parasites than thin films; primarily used when parasites are few in number or when thin smears are negative.

  ADVANTAGE: Increased ability to detect the malarial parasites

  DISADVANTAGE: RBCs have been lysed and it is not possible to access the morphology of parasite that are detected
• Finger-Prick Blood Samples

  = Method

  + Thin Films/Smears

  • Thick on 1 end and thin and feathery at the other end; done using two, clean glass slides (Wedge method)
  • Provide the best view of the malarial parasites in RBC; routinely used for parasite identification to species level.
  • Microfilariae are carried with the smear during preparation and typically are located at the edges or feathered end of the thin film.
• Finger-Prick Blood Samples

  = Method

  + Thin Films/Smears

  • Before a smear is reported as negative for the presence of parasites, a minimum of 300 fields should be examined.
  • The WBCs on the stained blood film serves as the quality control
  • If the smears are prepared from anticoagulated blood, which is more than an hour old, the morphology of both parasites and infected RBCs may not be typical.