Blood film evaluations as a quality control activity.

Correlation of the blood film with the blood-count parameters provides a means of quality control of results obtained by the counter. This requires the observer to be skilled in identifying significant morphological abnormalities. Reliable blood film assessment must avoid potentially misleading information resulting from cell distribution bias and morphological artefact produced by poor techniques in the preparation and staining of films. Thus, whilst concordance between instrument results and manual films provides control on the sensitivity, specificity and predictive value of the counter, conversely blood count results provide a check on the reliability of the blood film. The experiences with the United Kingdom external quality assessment program illustrate the strengths as well as weaknesses of the blood film evaluation.