Method Reduces Sloughing on Malarial Thick Blood Films

The gold standard for malaria diagnosis is the examination of thick and thin blood films—thick films containing 10 to 20 times more blood than thin films.

A potential complication of thick film preparations is sloughing or peeling of the blood droplet from the slide during staining or rinsing, resulting in the loss of sample.

Microbiologists at the Mayo Clinic (Rochester, MN, USA) compared two methods for improving thick film slide adherence, a scratch method (SCM) and dipping the slide in acetone method (ADM). The two methods were compared to the standard method (SM) of thick film preparation.

Standardized blood droplets from 22 malaria positive and 4 malaria negative cases, that had been previously examined, were concurrently spread on glass slides using the SM, ADM, and SCM. For the SM and ADM prepared slides, the droplet was gently spread to an approximate 22 mm in diameter spot on the slide using the edge of a second glass slide. For the SCM, the droplet was spread by carefully grinding or scratching it into the slide with the pointed corner edge of a second glass slide. Slides were dried for one hour in a laminar flow hood. For the ADM, slides were dipped once in an acetone filled Coplin jar and allowed to air dry. All slides were then stained with Giemsa and examined in a blinded manner. Adherence of the blood to the slide was assessed by reviewers who did not know the method used.


Slides prepared with SCM displayed both a lower frequency and a lesser severity of blood droplet-adherence defects than slides prepared by the SM or ADM. There were no instances of significant defects or severe defects observed for scratched slides. For the SCM the most frequently observed result was a completely adherent blood droplet (25/26), with only a single minor adherence defect. While completely adherent droplets were also the most common result for SM or ADM prepared slides, the incidence of adherence defects or sloughing was significantly higher for SM (9/26) or ADM (12/26).


The authors concluded that the scratch method was an inexpensive, rapid, and simple method that improves the adherence of thick blood films to standard glass slides without altering general slide preparation, microscopic appearance, or interpretability. The use of SCM, thick films can be reliably examined less than two hours after sample receipt. This represents a significant diagnostic improvement over protocols requiring extended drying periods. The study was published on July 8, 2013, in the Malaria Journal.

Related Links:
Mayo Clinic